I finally upgraded to a 7427 pcm, have some comments and questions

I swapped out the malfunctioning 8746 ecm in my 89 firebird formula (TBI on late '90's vortec 350 long block and TH700R4 trans)for a 7427 pcm last week finally and have run into a few situations that I wanted to comment on and/or ask questions about. First, I wanted to say that the actual swapping of the pins over to the new connectors was far easier than I expected. It did take a while, but I took my time and this was after putting in about 12 hours at work. I did want to note that I wired one circuit differently than how it was shown on the pin conversion chart. Instead of just moving pin C16 from the old ecm over to pin E13 on the 427, I took the brake switch input going to the TCC on the trans and routed it to pin E13 on the 427 pcm as it would normally be wired. I then simply ran an ignition hot wire to the TCC circuit on the trans connector. Since the TCC is unlocked by the ecm whenever you lift off of the throttle, this really isn't necessary. I had to wire-up the trans after I bought the car as it was originally a manual and was converted to an auto by someone that either didn't know how to or care to wire the trans so that the TCC would operate. I left the trans wiring fairly easily accessible so making the changes weren't difficult.

My first impressions were that the 427 conversion was definitely worth the time and relatively low cost. All driveability aspects are significantly better than the old 746 ecm could deliver. The amount of information available in the datastream makes tuning and monitoring much easier not to mention the datastream is so much faster. The amount of information regarding tuning and the amount of parameters that you can modify also make tuning much easier. I am still having a time finding the "sweet spot" regarding the ignition timing tables, but this morning I loaded the timing map from fast355's bjyl 350 tbi 700r4 bin and it appeared to be pretty good all the way around.

Before I ask a question I will describe my problem and then attempt a solution for the drive home and post the results. I installed the correct 4k knock sensor for the application. I went by the gm parts catalog for a 95 c/k 1500 5.7 vin k with auto trans and used a brand new delco sensor. My problem is that I am getting tons of bogus knock counts beginning right when I crank the engine. I bypassed the esc module by butting the black and white wires together near the module. I have used 2 different pcms and memcals with absolutely no difference. It will register between 200-500 knock counts while cranking to start. From there it will randomly register 25,50,100, or more counts at a time. I know the counts are bogus most of the time because of the counts it registers during startup and it will also register counts while idling. One possible cause I am considering and am going to eliminate is that the sensor wiring runs through the harness across the rear of the engine very close to the distributor and plug wires. I am using universal cut to fit accel spiral core wires and believe that I have some arcing at the cap due to the stainless conductor being pulled through the boots during assembly. My theory is that the wiring is picking up rfi and the pcm is interpreting that as a knock signal. I have a spare set of terminals and boots that I am going to install along with a new cap and rotor, but not tonight as I don't have time. But, I am going to fix the sensor wiring so that it runs straight through the main harness to the pcm and eliminating the loop that passes by the distributor. I was planning on doing that anyway, but was in a hurry to get the car running when I did the swap.

Gotta run for now, but more to come..........

Ok, so I fixed the knock sensor wire to route it directly from the sensor through the harness and to the pcm. Unfortunately it had no effect on the bogus knock counts while cranking. So if anyone has any suggestions I'm all ears. While rerouting the knock sensor wire I also was able to verify the resistance of the sensor and it came in right at 3998k ohms. I am stumped again on this one. The ONLY mechanical difference that I know of between the L31 and L05 that would affect mechanical engine noises would be the change to roller lifters on the L31 and I have never heard of that having an impact on knock sensor readings. I do know of other factors that affect knock sensor readings like roller rockers i.e. LT4 hotcam upgrade and the LT4 knock module that filters out the noise that the rockers generate. Just as I am typing this post I remembered that I used the GM Performance Parts heavy duty single roller timing chain and wonder if it is possible that it could be the culprit ? There is no reason to suspect excessive engine noise due to wear etc... as there is no audible noise from the engine as observed in the shop at idle and revving both with and without a load.

As far as all other factors of the upgrade go I am very pleased. But I do have a rather fundamental question that I have been wanting to ask regarding tuning in general. How does everyone that does not possess an emulator swap chips in their ecm ? I unplug the ecm every chip change which I find to be an arduous task that I also feel to be rather hard on the terminals in the connectors. The only other way I know would be disconnecting the battery which is even more inconveniencing since you lose your clock setting and radio presets. Anyhow, I need to head to bed. I will try to make an effort to post a bin and datalog tomorrow for anyone that wants to examine.

Ok, so I couldn't rest until I verified that the chain kit that I used contains all of the same part numbers that the service catalog lists for the L31 in heavy duty applications and the knock sensors are the same for both regular and heavy duty. The only thing that could be different would be the knock module which I will look up tomorrow, but doubt it is different. So, that brings me back to square one....................

You did bypass the ESC, correct?

The '7427 has the knock sensor connect directly to the PCM.

I don't remove power from the ECM, or unplug it when I swap EPROMs, never had an issue.

In a friends car, I do use a remote socket from Moates (Chip Extender 1.0), and just swap EPROMs using that and a ZIF socket. I tune his car using an Ostrich though.

I've used the Moates.net G1 memory adapter with a ZIF socket http://www.moates.net/gp1-package-gm...h-2-chips.html to make chip swapping easy. I've even swapped chips out and into the ZIF socket when the was battery connected, with the ignition switch off! I can't recommend swapping chips with the battery connected, so maybe I've been lucky a few dozen times.:innocent2:

I've also seen bogus knock counts after swapping to a '427 PCM. I think the knock module in the Memcal could be the problem? In a couple instances, I've swapped Memcals and the bogus knock counts were cured. In a couple instances, I simply disabled the knock sensor in the PROM programming.

dave w

I bypassed the esc module and also rerouted the knock sensor wire so that it runs directly to the pcm instead of simply cutting the wires at the esc module and butting them together which I did do initially to save time. I also tried a different memcal and pcm with no change at all. As far as chip swapping goes, I had trouble with the 8746 and also a nissan 240sx that I used to own if I changed chips without removing battery power. In both it seemed that I could get away with 1 or 2 swaps and then they would exhibit some very bizarre behavior. I haven't attempted to swap chips with the 427 without unplugging it yet. I have the moates adapter for memcals but I primarily use a memcal that I soldered a 27sf512 in place of the original chip.

You could pull the PCM fuse, or if you're really that worried about it, you could install a switch or N.C. momentary button in place of the main power into the PCM that you switch off when ever you need to.

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Originally Posted by Six_Shooter

You could pull the PCM fuse, or if you're really that worried about it, you could install a switch or N.C. momentary button in place of the main power into the PCM that you switch off when ever you need to.

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My very first thought upon reading that was DUH ! Why has that never crossed my mind ?!?! I guess it's one of those simple things that some people like myself will over-complicate. I had wondered if disabling the checksum had anything to do with chip swapping like it does when emulating. This is a rather unimportant topic versus the rest of my woes though.

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Originally Posted by dave w

I've used the Moates.net G1 memory adapter with a ZIF socket http://www.moates.net/gp1-package-gm...h-2-chips.html to make chip swapping easy. I've even swapped chips out and into the ZIF socket when the was battery connected, with the ignition switch off! I can't recommend swapping chips with the battery connected, so maybe I've been lucky a few dozen times.:innocent2:

I've also seen bogus knock counts after swapping to a '427 PCM. I think the knock module in the Memcal could be the problem? In a couple instances, I've swapped Memcals and the bogus knock counts were cured. In a couple instances, I simply disabled the knock sensor in the PROM programming.

dave w

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Regarding the G1 adapter and ZIF sockets, I do have that exact adapter as I stated in my earlier reply. I have always used ZIF sockets for chipping ecms with the exception of the modified memcal I made for this project and buy all of my hardware from moates.net (product plug ! lol).

I also have disabled the knock sensor flag in this pcm once as I didn't get the correct knock sensor until a day after the install and the pcm didn't like the 100k ohm knock sensor already in the car. I also backed the pin out of the pcm connector until I installed the correct sensor. What I did find odd was that the pcm would still register knock counts with the 100k ohm sensor plugged in even with the knock sensor code set (I always forget if it's 42 or 43 because the other code is the est/bypass code that sets when setting distributor timing). My concern with disabling the ks is detonation that I cannot hear as the combination of the very open intake and accompanying noise and the exhaust make it hard to hear any pinging at wot. I may disable the ks for now and back off of the timing a little until I find a solution.

Another issue that I have noticed is that I cannot get the pcm to operate the ccp solenoid for some reason and I thought that I had checked and set all of the ccp parameters in the bin. I have already verified the circuit integrity and solenoid operation. The old ecm quit commanding the solenoid when it started taking a dump so I temporarily wired the solenoid so that it activated with the ignition on and it was working when I did the swap. I had seen somewhere in either this or another forum a few posts regarding the ccp operation when installing a 427 pcm, but forget the details. I am going to double check everything before I burn my next chip and see if I can find the cause.

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Originally Posted by pmkls1

Another issue that I have noticed is that I cannot get the pcm to operate the ccp solenoid for some reason and I thought that I had checked and set all of the ccp parameters in the bin. I have already verified the circuit integrity and solenoid operation. The old ecm quit commanding the solenoid when it started taking a dump so I temporarily wired the solenoid so that it activated with the ignition on and it was working when I did the swap. I had seen somewhere in either this or another forum a few posts regarding the ccp operation when installing a 427 pcm, but forget the details. I am going to double check everything before I burn my next chip and see if I can find the cause.

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What bin are you running? Most bins I looked at did not have ccp selected, and most of the parameters looked ok, but a few were either maxed out, or set to min, so I doubt just selecting the flag to turn it on will make it work. I am getting ready to install a ccp solenoid and controll it with the pcm (I am also running a 7427) When I got me a ccp solenoid from the junkyard, I got it from a 95 surburban, witch by chance, still had the pcm in it, so I grabbed that too. The bcc is BJYK, I checked it and ccp was active in it, so I opened two instances of tuner pro and copied every single parameter for ccp from BJYK and put them into my bin. BUT, I have not actually had a chance to install the solenoid yet and hook it up. I am hoping to have some time this weekend, so it hasnt been tested yet. I think BJYK is in the $0D thread, if not, let me know and I can post it up.

But back to your originial question, I really cant help you, as mentioned above, I am also running a 7427, however mine is a conversion (jeep 401 V8) I too get thousands and thousands of knock counts. I was unable to get it to work correctly, so I have simply disabled knock retard and have tuned by ear.

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As far as chip swapping goes, I had trouble with the 8746 and also a nissan 240sx that I used to own if I changed chips without removing battery power. In both it seemed that I could get away with 1 or 2 swaps and then they would exhibit some very bizarre behavior.

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This could be from the BLM learn and you changed fuel VE tables?

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My very first thought upon reading that was DUH !

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I hate when that happens! :homer:

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Before I ask a question I will describe my problem and then attempt a solution for the drive home and post the results. I installed the correct 4k knock sensor for the application. I went by the gm parts catalog for a 95 c/k 1500 5.7 vin k with auto trans and used a brand new delco sensor. My problem is that I am getting tons of bogus knock counts beginning right when I crank the engine. I bypassed the esc module by butting the black and white wires together near the module. I have used 2 different pcms and memcals with absolutely no difference. It will register between 200-500 knock counts while cranking to start. From there it will randomly register 25,50,100, or more counts at a time. I know the counts are bogus most of the time because of the counts it registers during startup and it will also register counts while idling. One possible cause I am considering and am going to eliminate is that the sensor wiring runs through the harness across the rear of the engine very close to the distributor and plug wires. I am using universal cut to fit accel spiral core wires and believe that I have some arcing at the cap due to the stainless conductor being pulled through the boots during assembly. My theory is that the wiring is picking up rfi and the pcm is interpreting that as a knock signal. I have a spare set of terminals and boots that I am going to install along with a new cap and rotor, but not tonight as I don't have time. But, I am going to fix the sensor wiring so that it runs straight through the main harness to the pcm and eliminating the loop that passes by the distributor. I was planning on doing that anyway, but was in a hurry to get the car running when I did the swap.

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Running a EFI harness to close to distributor or spark plug wires in a conversion has caused many issues with RFI noise so this is always a possibility. But you keep saying how load this car is with headers and exhaust! Known issue! Some camaros will get knock counts and retard from rear axle control arm bushings, so anything that makes noise even that far away can cause knock counts. De sensitizing the Knock Sensor has worked, first step would be several wraps of teflon tape and since you know better not to over tourqe the knock sensor, second step would be a brass fitting or elbow is sometimes needed. Of course any rattle during cranking or running will set it off too.

You didn't mention the mask but I am assuming $0D, there is a catagory with some paremeters that may help "Knock Retard Paremeters" to disable knock. Turning off the Code 43 will only turn off the CEL, not the circut. Also is there Spark Retard happeneing when getting these knock counts?

I wonder what would happen if knock sensor input was connected to a 4K ohm resistor? Connect one side of the resistor to B15 and have the other side of the resistor connected to battery negative? In my thinking, a constant 4K input should eliminate knock counts, figuring everything inside the Memcal / PCM are working correctly?

dave w

I'm Short on time so I'll make this response quick. I'm running an $OD mask and the bin is based off of a BJYL bin. . I have been logging since the install but have only had time to glance at the logs thus far but looked closer this morning and had a major breakthrough regarding issues that date back to the install of the L31 vortec long block. I noticed while watching a pull at wot up to 5k rpms that the engine speed was fluctuating a lot and got worse as the rpms got higher. The problem is that the engine speed want actually fluctuating during that run so I watched the rest of the drive and verified that the fluctuation shows up under normal conditions as well. Sooooooo, "houston, we have a problem". Only this time I know exactly where to look. The problem could be inside the dizzy OR the wiring as I did have the dizzy apart during the engine install to replace the gear and also remove the rust where the rotor installs because it was getting to be near impossible to remove/install the rotor. Either way, I'm going to just replace the 220k mile dizzy as well as go over the wiring since the harness could easily have gotten pinched during install as itt runs right across the top of the trans bellhousing. I am positive that this condition is the cause of most of my problems and that it only occurred after the engine swap and have not been able to identify it until now because the fluctuation does not register on the tach which is most likely buffered and the 8746 data stream is so slow that it would most likely not show up on a datalog. I have had the same issue before when a map sensor went bad. The car would lunge and nearly stall when pulling out from a stop but I could not figure out why because the sensor would still read sort of correctly but it was very slow to respond to changes in vacuum so by the time the data would update on the screen the map readings looked fine. Anyway, I gotta run. Hopefully I will have a new dizzy I installed and the wiring checked and/or fixed tonight. I will post as soon as I have verified that the issue has been corrected.

That is also a cause of EFI wires to close to high voltage spark.

Good point, but I'm tired of having to stay late at work to fix it so I'm going to go ahead and replace the dizzy and inspect the harness along with the plug wire repairs/rerouting that I had planned just to eliminate most of the probable causes. I am also going to double check the pins at the pcm connectors for proper pin tension and repair as needed.

Based on my experience using the L31 camshaft / TBI distributor combination, I install a new Melonizied distributor gear.

http://paceperformance.com/i-6251232...rnal-coil.html
It's my understanding the steel used in the L31 camshaft will destroy:yikes: the cast iron TBI distributor gear.

Maybe, just maybe the TBI cast iron distributor gear and L31 steel camshaft are the source of the knocks?

dave w

Simple answer would be I replaced the dizzy gear during the engine swap as the old one was shot and made sure to verify that it was a melonized gear. But FWIW, by TBI distributor I am assuming that you are probably referring to an L03 or L05 C/K truck engine distributor as those were the most widely used TBI engines. However, the L03 and L05 truck only applications were the only SBC engines that did not receive the roller cam upgrade in 1987. All other gen 1 SBC engines from 87 up were equipped with roller cams and used the same distributor regardless of induction type including the car versions of the L03 and L05. Just an FYI, LT engines are considered gen 2 and L30/L31 applications were considered gen 1+. While 86 and prior SBC engines using flat tappet cams and perimeter bolt valve covers are considered gen 0 with the exception of the 86 corvette L98 which used both benter bolt heads and a roller cam. I am stepping out on a ledge here and assuming that the distributors installed in the roller cam engines used a melonized gear as they did have a relatively acceptable service life. Nowadays, these 20+ year old high mileage distributor gears do require replacement due to wear and sometimes wear enough to actually lose contact with the cam and thus not rotate. But it is my understanding that a cast iron distributor gear won't last maybe 20K miles or so when mated to a billet steel roller cam. Nowadays most OE style replacement small cap EST HEI distributors have been consolidated to a single part number and are equipped with a melonized gear and I am under the impression that a flat tappet cam is compatible with a melonized gear. And even cheap replacement gears for roller cam applications are in fact melonized. But, that's way more info than needed.

Now, I don't mean to come across as argumentative I just have thought the issues through over and over again. Gotta go for now, need some sleep bad,

Phil

Cool, your using a melonized distributor gear. Didn't know until I asked.

dave w

Yeah and from what he said I need to change my distributor! 140K flat tappet TBI truck motor. Maybe using synthetic with zinc and phosphorous all these years has paid off besides the lifters?

I hope you didnt think I was being a smartass dave because I wasn't. I respect and appreciate all of you veteran gearheads posting ideas and suggestions in this thread. I was just sharing some info in case you didn't already know.

Mark, in my experience the C/K L05 had almost no issues with the lustered even at mileages past 200k. They did, however, frequently require replacement of the distributor gear at higher mileages. If you haven't had the distributor out in some time I would check the gear. In many cases even severely worn gears may not exhibit any noticeable driveability concerns. This was the case with the dizzy in the old 305 that came out of my car and I do realize that I am jumping back and forth between roller cam and flat tappet engines, but the issue was fairly consistent across the board with the small cap distributors of the era. Back to my car, I had pulled the distributor last year for reasons I can't remember and noticed a severely worn gear but didn't replace it because I was unsure of my plans at that point. I did have one ready come time for the engine swap. By then you could probably have shaved with the teeth they were so thin, yet thre were no driveability issues at all. It did probably affect performance, but on a 200k+ mile engine it would hard to tell. And regarding zinc and synthetic oil, I am a firm believer in both. The assembly lube that GM used called engine oil supplement or EOS for short is loaded with zinc and one of the uses listed on the label for years was as an additive to engine oil, but it was removed from the label after a link between zinc and catalytic converter damage was made somehow. Well gotta go,
Phil

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Originally Posted by pmkls1

I hope you didnt think I was being a smartass dave because I wasn't. I respect and appreciate all of you veteran gearheads posting ideas and suggestions in this thread. I was just sharing some info in case you didn't already know.

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We're good. Didn't think that you were being a smartass at all. The discussion of using a melonized distributor gear is "valueable information" to this thread.:thumbsup:

I'll also add, the "off-shore ~ $$ Cheap" aftermarket TBI distributors (1987 ~ 1995) use an 11mm shaft. The link I posted for the GM melonized gear will not fit an 11mm shaft!:yikes: I really doubt the "off-shore ~ $$ Cheap" aftermarket TBI distributors will install a melonized gear, considering the melonizing process was most likely not an OEM spec back in the day? Most likely GM would use different distributor shaft sizes to keep melonizied / non-melonized gears from getting on the production line for engines needing / not needing melonizied gears?

dave w

I read on TGO that this pcm does a knock test on startup and knock counts are normal (only at startup). I get a bunch of bogus knock counts when I crank mine too, but it has never posed a problem for performance. I get no knock counts after startup and no KR.

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Originally Posted by dave w

We're good. Didn't think that you were being a smartass at all. The discussion of using a melonized distributor gear is "valueable information" to this thread.:thumbsup:

I'll also add, the "off-shore ~ $$ Cheap" aftermarket TBI distributors (1987 ~ 1995) use an 11mm shaft. The link I posted for the GM melonized gear will not fit an 11mm shaft!:yikes: I really doubt the "off-shore ~ $$ Cheap" aftermarket TBI distributors will install a melonized gear, considering the melonizing process was most likely not an OEM spec back in the day? Most likely GM would use different distributor shaft sizes to keep melonizied / non-melonized gears from getting on the production line for engines needing / not needing melonizied gears?

dave w

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Sorry it took me a couple days to reply, but I developed a nasty sinus infection that hit me pretty hard. Well, you just told me something about the cheap offshore distributors which I believe come from china and are knock-offs of the original part # units. The cheap aftermarket parts I was referring to would cardone and bwd, which are probably of significantly higher quality in comparison with the china made parts. I also had a momentary lapse in brain activity about part # consolidation. It is the complete distributors and NOT the gears that have been consolidated to a single part #. The gears listed on the autozone and advance differ by application but a complete distributor has one part # for all. You will also find the same to be true for some other aftermarket distributors marketed to fit "late model efi applications" such as in the performance parts sector. I know that jegs sells one under their brand that mentions nothing about camshafts until you read the instructions and then steel roller camshaft is mentioned. Otherwise, though, information is a little difficult to come by regarding what type of gear is on the distributor as many will just claim to fit 87-95 applications for cars and trucks. I cannot find it now, but I swear that I saw a note on the BWD gear for a roller cam application indicating that it was such during my search for some sort of evidence that the part I would be buying would be melonized. The info I found may have actually on a sheet included with the part. The important thing would be that the gear is "supposed" to be correct for the application.

As far as GM parts go this is what I do know. I know that the GM catalog has been updated many times and that most of the original part numbers have been superceeded, but the OE GM distributors must have all had the same diameter shafts as the parts catalog shows the same part #'s for the housings, shafts, and gears. The gear you listed p/n 19052845 is also listed in the catalog as the replacement p/n for all applications and is installed on the distributor p/n 1103952 that is sold both as a service replacement for the trucks and cars. It is also sold through the GM Performance parts catalog as a "late model efi distributor". That part number is a fairly old part number and is easy to tell because it is a 7 digit number. 7 digit part numbers are numbers that have been around for a long time and are technically an 8 digit number with the first digit being 0 that can be and normally is left off. Oddly enough, I recently had a conversation with one of the parts guys at work that was on this very topic. I have a lot of confidence in anything he says and trust him especially on vehicles of that era since he has sold chevolet parts longer than I have been alive. When it comes to parts from "the good ole days" he can still remember many of the commonly used parts and pull them right up in the computer without having to look them up. I asked him about a small cap distributor and he instinctively pulled up that number without hesitation. I asked if he had sold many of that number and he said that was the only distributor he knew of for 87-95 applications and had sold tons of them.

One last note that I will add is that in the GM performance parts catalog in the distributors and components section there are a couple notes stating that a melonized gear MUST be used be used on all crate engines or serious damage will occur. The odd thing about that statement is that many of their crate engines use flat tappet cams. Their standard big cap HEI that they sell out of the catalog for carbed applications also comes standard with a melonized gear. Anyhow, long story short, it would appear that a melonized gear is compatible with a standard flat tappet cam and that many of the trucks have had this distributor installed

How would you go about getting a new small cap EFI distributor? I tried GM Performance online and that part number and no go?

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Originally Posted by EagleMark

How would you go about getting a new small cap EFI distributor? I tried GM Performance online and that part number and no go?

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I'm not sure what site you went to, but you can get that distributor anywhere including jegs and summit or the local gm dealer. Just google 1103952 distributor and you'll get tons of results.

Must have sucked at search cause that worked good! Thanks!

No prob. And back to the topic of my ignition problems, I happened to stumble across another finding. As I was double checking the listings for distributors and gears this weekend I found an error in the catalog for my car. If you look up a distributor gear for an 89 firebird formula 5.0 "E" in the bwd catalog (which is the brand that advance auto parts carries) they list a gear for a standard flat tappet cam. I only realized that the part number was wrong after comparing a few vehicles. But, if you look up a gear for an 89 camaro 5.0 "E" the correct gear is listed. So, long story short, I am NOT running a melonized gear on my dizzy giving me yet another reason to buy a new dizzy. Since I do not know the cause of the erratic distributor reference signal and do know that the module and pickup are cheap aftermarket pieces and that the gear is incorrect I would want to replace all 3 components. And, the combined cost of those components from GM is nearly as much as a complete distributor. I don't have the $$$ for a new dizzy this week, but luckily the weather forecast looks like I'll be riding the bike a lot.

I did resolve the CCP issue and it is now functioning. I also have a timing curve that seems to work well overall. I haven't done much with the VE tables yet, but really don't plan on doing much more tuning until I get the ignition system straightened out.