Recommend an ECM to replace my 8747?

[dpilot83]

I wonder if this ECM even came with my truck originally. I have a 93 K3500 w/ 7.4 and NV4500. PO told me the engine was not the original engine. I believe it was a used 80,000 miles engine pulled from another vehicle. I wonder if he pulled the ECM at the same time because the 8747 info page (http://www.gearhead-efi.com/Fuel-Injection/showthread.php?521-1228747-ECM-Information-4F) does not list my year and model as a possibility. Maybe that is just not a complete list?

Anyway, I have suspicions that the current ECM could be struggling and I was considering getting into tuning. Both of those things would point me towards a different ECM and the tuning aspect leads me towards an ECM that has more support for it like the 7747, 7060 or a 7427?

I would imagine with any of those I would have to re-pin the harness that plugs into the ECM (Except maybe the 7747?). Anything else I should be considering? Thanks.

[dave w]

I'm thinking the original ECM was 16171199. The wiring diagrams for ECM's 1227747, 1228747, and 16171199 are nearly identical. I would tune the 1228747.

http://www.gearhead-efi.com/Fuel-Injection/showthread.php?521-1228747-ECM-Information-4F

dave w

[brian617]

According to my interchange the 1228747 is more than likely the original ECM given that it is a 7.4L manual trans. The other two choices for that application are 16147060 and 16168625 used in automatics.

[dpilot83]

According to my interchange the 1228747 is more than likely the original ECM given that it is a 7.4L manual trans. The other two choices for that application are 16147060 and 16168625 used in automatics.

What do you mean by your interchange? Another person I talked to who had me convinced he knew what he was talking about said that it should have the 8747 in it. Since both you and another person said it should have a 8747 in it, does that mean the page dave w and I linked to is not very complete? Thanks.

[brian617]

Hollander parts interchange, I work in a salvage yard.

[dpilot83]

I'm thinking the original ECM was 16171199. The wiring diagrams for ECM's 1227747, 1228747, and 16171199 are nearly identical. I would tune the 1228747.

http://www.gearhead-efi.com/Fuel-Injection/showthread.php?521-1228747-ECM-Information-4F

dave w

There is a guy on 454ss who seems to really know 454 TBI trucks who said I should expect to have the 8747 in it as well. Between that and brian617, I wonder if the link you provided (I had already seen it which is why I wondered if I had a different ECM) is incorrect or incomplete?

Anyway, the reason I'm considering replacing the ECM is because of a problem I'm having with the engine stalling anytime the engine compartment gets hot enough. I admit that since the ECM isn't in the engine compartment, that's kinda grasping at straws, but that's the point I'm at now.

Anytime the engine compartment is warm (idling for awhile on a hot day) it starts idling erratically and then it finally stalls. When I try to re-start it is very difficult to get it to start.

It's very difficult to diagnose because I cannot make it do it with the hood open and the air cleaner off. I think it would idle all day in 110 degree weather with the hood open and the air cleaner off so that I can watch injectors and spark while it happens.

If I make it happen with the hood closed and then quickly remove the air cleaner and install a spark tester and try to restart it, it has spark but the fuel flow from the injectors is not the same as it would be on a normal start. You can see the spray but it's just very light. I have had the throttle body rebuilt and injectors tested and balanced by SPR Performance (tbiparts.com run by dctrumpet on thirdgen.org). I have also installed a fuel pressure gauge at the back of the throttle body and it is always between 11 and 14 pounds, (usually about 13). There are no codes (other than an occasional code 43 which just started happening for some reason). The entire ignition system is new, meaning new loaded distributor, new plugs, new wires, new coil (all OEM parts). I set the timing with the wire disconnected. A compression test reveals about 125 PSI which is withing standards for the L19 which came from the factory with pretty low compression.

So I guess I'm down to wondering if there is a wiring problem or if the ECM is bad. Hence my question in the other thread about how to test the ground wires in particular.

Anyway, it's been a challenge. Between wanting to tune it after I finally get it figure out and the possibility that the ECM (dctrumpet suggested that the injector drivers in the ECM could be flaky) is causing problems, I'm considering switching ECM's. Hence my question as to which one would be good for this truck.

Another consideration is that I could imagine someday wanting to put a 4L80E in it. I think that would lead me quite directly to the 7060 ECM, but I'm not sure how likely that is. I do like 5 forward gears, but I've had enough clutch problems that I wouldn't mind getting rid of that headache as well.

[dpilot83]

I'm thinking the original ECM was 16171199. The wiring diagrams for ECM's 1227747, 1228747, and 16171199 are nearly identical. I would tune the 1228747.

http://www.gearhead-efi.com/Fuel-Injection/showthread.php?521-1228747-ECM-Information-4F

dave w

Since this thread is sorta about the 8747 and you're a moderator, why is the 8747 thread at the top of the page a sticky? Just curious...

[EagleMark]

What do you mean by your interchange? Another person I talked to who had me convinced he knew what he was talking about said that it should have the 8747 in it. Since both you and another person said it should have a 8747 in it, does that mean the page dave w and I linked to is not very complete? Thanks.
Interchange is a book that salvage yards use to find parts.

There's a possibility that any of the info pages are not complete, we do the best we can. It's been verified the ECM came in your truck so I don't think that is your issue. Grounds from ECM back to engine can always be an issue so check them on engine block, there's normally two sets of grounds, one near T stat housing and one on back of head or intake.

From your description of problems I really doubt you have an ECM issue. Since the ECM is not under hood and you've obviously got an overheating under hood issue. I think you mentioned an engine change? I'd be looking at fuel lines first from your symptoms? It sounds like the fuel is boiling, you know like old carb vapor lock. It happens to TBI as well. See that the fuel lines are routed properly as they run from TBI down the frame near the exhaust etc...

[EagleMark]

Since this thread is sorta about the 8747 and you're a moderator, why is the 8747 thread at the top of the page a sticky? Just curious...Me too? Who made that a sticky? I just don't see a reason for it?

[dave w]

Me too? Who made that a sticky? I just don't see a reason for it?

I don't think I made the post a sticky, maybe I unintentionally did. I don't think the sticky is an option in the Moderation Tools? Is there a short cut key / hot key that would make a post a sticky?

dave w

[JeepsAndGuns]

Just to confirm what has already been confirmed. I am currently (trying to) part out a 93 C3500 with a 454 and 5 speed. It too has the 8747 ecm with the bcc ARPY. It appears to have nmever been removed and I would believe its factory.

If you were to swap to a different pcm, say for instance a 7427, the hardest part is going to be finding a 454 memcal. Right now your ecm uses the knock filter seperate from the ecm.

[dpilot83]

Just to confirm what has already been confirmed. I am currently (trying to) part out a 93 C3500 with a 454 and 5 speed. It too has the 8747 ecm with the bcc ARPY. It appears to have nmever been removed and I would believe its factory.

If you were to swap to a different pcm, say for instance a 7427, the hardest part is going to be finding a 454 memcal. Right now your ecm uses the knock filter seperate from the ecm.

I wish you were closer, especially if your pickup was a crew cab with a tan interior. I need a rear seat (employee spilled gear oil all over it) the glove box hinge piece, and I'm sure about a zillion misc pieces that I am not thinking of right now.

I haven't heard of the knock sensor being separate from the ECM. Can you elaborate on that more? Thanks.

[dpilot83]

there's normally two sets of grounds, one near T stat housing and one on back of head or intake.

I have found the set on the thermostat housing. I'll look for the other at the back of the intake manifold. Thanks.




From your description of problems I really doubt you have an ECM issue. Since the ECM is not under hood and you've obviously got an overheating under hood issue. I think you mentioned an engine change? I'd be looking at fuel lines first from your symptoms? It sounds like the fuel is boiling, you know like old carb vapor lock. It happens to TBI as well. See that the fuel lines are routed properly as they run from TBI down the frame near the exhaust etc...

That's an interesting observation. I've owned this pickup for several years before it started doing this. It has never idled quite right and has missed occasionally under load, etc but it has not done this particular thing except for this year now that it's gotten warm. This winter we had SPR rebuild the throttle body and we added a fuel pressure gauge behind the throttle body. The fuel pressure gauge required quite a bit of manipulation to get the adapter installed between the throttle body and the steel fuel line. Perhaps the manner in which we manipulated the line caused it to be in a hotter area? I really don't think we moved it hardly at all, it's just that even moving it that small amont was quite difficult.

How would you know whether the fuel in the lines are boiling or not? My pressure gauge always stays pretty steady. Honestly, I would not be at all surprised because it's pretty clear that something is coming out of the injectors, it's just not coming out as much as it does during a cold start.

This is actually quite fascinating to think about. It would explain everything. It would explain:

1. It looking like there is fuel coming out but it looks like not as much as a normal start
2. It only happening while the engine bay is very hot
3. How when it starts it kinda sputters to life and the more you get it going the better it runs and the better it runs the easier it is to keep it running. It's just introducing cold fuel into the lines that makes it run better and better the more it gets rid of the hot fuel. Revving it to 3000ish RPM simultaneously pulls a lot of air in and gets rid of a lot of hot fuel

[EagleMark]

All that fuel line has to do is hit a hot piece of metal and POOF! Vapor lock.

You could also be on the verge of needing a fuel filter? Many times I've seen them work fine but the reduced flow would cause data to change...

Revving motor to 3000 RPM also increases fuel flow by raising voltage just a little to pump. This would circulate all excess fuel back to return and cool things off.

I think you have some sort of hot fuel issue? :popcorn:

[dpilot83]

You could also be on the verge of needing a fuel filter? Many times I've seen them work fine but the reduced flow would cause data to change...



Is there any way for the fuel filter to be plugged if your pressure at the back of the throttle body is staying up? I do not have my remote electrical gauge hooked up so I don't know what the fuel pressure is doing under load, but I'm also not having any problems with it not running right under load, it's just during idle. During idle, even when it dies or when there is a hard start/no start situation the fuel pressure is always good (usually about 13 PSI).

[gregs78cam]

I recently had an issue with my truck's tbi conversion. The fuel lines had gotten too close to the exhaust and it was having boiling fuel issues. It would run fine until it got warm, it would always do it, but when it did it would stumble when you got to about 30%TPS. Idle was just fine though.

The other issue I ran into recently was on a buddy's truck, where the fuel pump was not making enough pressure at any state other than idle. The thing that tipped me off was that when in closed loop it was pegging max lean.

These are just my two recent discoveries with TBI. Were your injectors replaced with the TBI rebuild? Is their power wire corroded? getting hot? not able to carry enough current? Could this be combination of issues, i.e. injectors that get flakey at low pulsewidths, such as hot idle?

A datalog might reveal some interesting trends.

[JeepsAndGuns]

I wish you were closer, especially if your pickup was a crew cab with a tan interior. I need a rear seat (employee spilled gear oil all over it) the glove box hinge piece, and I'm sure about a zillion misc pieces that I am not thinking of right now.

I haven't heard of the knock sensor being separate from the ECM. Can you elaborate on that more? Thanks.

The knock sensor is always seperate from the ecm, its threaded into the block somewhere. Its the knock filter I was talking about. Its what recieves the signal from the knock sensor when there is knock, and then sends a signal to the ecm to retard timing. The knock sensor and knock filter are engine specific. On yours, its the squareish shaped flat box with about 4 wires going into it, should be mounted beside or under the map sensor on the right of the intake. (it was on the truck I am parting out anyways)
On the later pcm's (such as the 16197427) the knock filter is part of what is called a memcal. It has the main prom chip, the limp home chip, and the knock filter all in one removable unit in the pcm. The V6 and 5.7 memcals are easy to find, but a 7.4 memcal is not as easy. You could use a 5.7 memcal, and re tune the chip to work with the 7.4, but the knock filter will be incorrect and the knock retard will not function correctly. It could either pick up false knock and retard your timing, hurting performance, or not pick up knock that is there, and then your engine could get damaged.

[dpilot83]

I think the vapor lock theory is losing traction after today. I used it a fair amount today. One time I drove about 15 miles, stopped for 15 to 20 min to eat and then started it again and it had a tough time starting. Outside air temp was 64 degrees F (18C) at that time. Lots of cloud cover here today.

The next example was more significant I thought though. I stopped to help my wife clean the church after another 20 mile drive. When I stopped I immediately opened the good to help it cool down faster. We probably spent 15-20 min finishing the cleaning of the church. We decided to go eat afterwards so. I started my pickup to park t more out of the way in the parking lot. It started fine and I ran it for maybe 1 minute changing parking spots. I did not open the good this time because I figured it would not have warmed up much. We spent probably 30-40 minutes eating and came back to get the pickup. It barely started again and ran really rough until I got it revved to 3000 RPM.

So whatever it is, I think it's getting worse. I'm quite puzzled that twice today it appeared to break the heat related rule. So far in the past it has only done it when it was 80+ degrees outside and it had been idling awhile.

Not so today.

i need to go ahead and get everything that I need to start logging data. I'll probably just order tonight.

[dpilot83]

The knock sensor is always seperate from the ecm, its threaded into the block somewhere. Its the knock filter I was talking about. Its what recieves the signal from the knock sensor when there is knock, and then sends a signal to the ecm to retard timing. The knock sensor and knock filter are engine specific. On yours, its the squareish shaped flat box with about 4 wires going into it, should be mounted beside or under the map sensor on the right of the intake. (it was on the truck I am parting out anyways)
On the later pcm's (such as the 16197427) the knock filter is part of what is called a memcal. It has the main prom chip, the limp home chip, and the knock filter all in one removable unit in the pcm. The V6 and 5.7 memcals are easy to find, but a 7.4 memcal is not as easy. You could use a 5.7 memcal, and re tune the chip to work with the 7.4, but the knock filter will be incorrect and the knock retard will not function correctly. It could either pick up false knock and retard your timing, hurting performance, or not pick up knock that is there, and then your engine could get damaged.

I see. Thanks for the explanation. I understood that the knock sensor was separate from the ECM (I meant to say knock filter in my previous post, sorry about that). I had just never heard of the knock filter before.