Timing issues? 16197427 93 TBI

Howdy

First time posting questions here. New to TBI tuning in general. More of a tinker project than anything really. Trying to learn something new. Apologies ahead of time for being long winded.

I have all the required Moates autoprom goodies and TunerPro RT and ready to jump in there but I am having some issues getting reliable timing setup. I have burned a couple of chips just to see how the process works but other than changing the Injector size and engine displacement, not much programming at all. This is a fresh rebuild and seemed to run fine on the engine stand using a carb and MSD vacuum advance but now I have the TBI installed and have some strange timing stuff happening. I have not tried much programming at this time mainly because I want to start with a stable base line and the timing jumping around is not giving me the warm fuzzy at the moment. Not sure if what I am seeing is normal or not as I have never worked with computer controlled distributor before]

Here is the engine setup:

1967 350 2bolt main 2pc rear main. [It was handy]
10.6:1 compression static. I checked out the Dynamic compression calculators and the one I feel most comfortable with is telling me 9.8:1 Dynamic.
Eagle .040 over balance rotating assy with bushed rods, 12cc dished pistons [not forged] Plasma Molly rings. This is the $800 set not the spendy stuff but we are not getting crazy here. Just tinkering.
.050 Squish-on the money. Was hoping for .040 but w/e.
601 heads ported per Fast305 outline on TGO minus the chamber grinding. [1.84 intake 53cc chamber. Yes I cc'd the chambers. They are 53cc. Intake and heads are port matched. I did measure the relative intake runner dims per outline from Fast305 at the time but I did not record the numbers. Bowl blending the same. It was very close if not exact. Installed Stainless valves hand lapped, new springs from Howards, New Viton seals etc. Guides looked pretty good. No more than .002 side wiggle. Also smoothed the cooling passages best I could.
Rt44 short plugs
8mm wires suppressed
New Accel distributor [questioning the ign module currently] Pertronix external coil
Performer style square bore dual plane manifold made by Dart
1" open spacer with 1/4" square bore to TBI adapter
Rebuilt TBI myself. Removed ridges, new injectors supposedly 'flow matched' @71/lb.hr @ 15psi. Installed 18psi spring. All the vacuum ports were thoroughly cleaned also.
Shorty 1.5" headers, 2.5" Y-pipe, Heated 02 in the collector, 3" single to dual 2.5" out Thrush muffler
Elgin stainless roller rockers[1.5]
Shorter push rods to accommodate the block milling and thin .015 steel gasket. Ie. rollers appear to be centered and tracking correctly. Valve lash set @ just shy of 1/4 turn. 5W20 oil.
High volume oil pump. [Leftover from a previous lifetime. Second guessing the high volume pump now. PLENTY of oil pressure though :thumbsup: ]
Oh. The Cam is a Lunati 60101 [Dual pattern .454int, .468exh, .213int @.050, .219exh @ .050] Also from a previous lifetime.
Computer is 16197427 with $0D, [4l60E next on the rebuild list.]
New radiator, engine temps staying under 180F
EGR turned off VIA EGR-on temp. CCP is still hooked-up and working according to the scanner.

I had some backfire through the exhaust and it is mostly gone since putting the baby-tune 1/8-ish turns on the valve lash. Mostly gone means the frequency has been reduced to several back fires per couple of seconds to one every 5-10 seconds at idle.
I set the base timing @ 10adv, set initial timing in program to same. Have done the same @0adv. No knock counts to speak of. 2 [counts at start-up]

When the brown wire is disconnected at idle, timing is stable minus the slight retard seen [at the balancer] when the exhaust backfires.
As I increase the RPM to 1500 or so, the timing jumps an additional 7adv and stays there regardless of increasing/decreasing RPM. It immediately drops back to the set point once back under 1500rpm.

With the brown wire plugged back in, I am seeing a lot of retard [10+ Ret] as the RPM increases.

In both cases, if the throttle is goosed, it can backfire through the TB and die or if treated with less aggression will stumble for a bit then take-off.

I am hoping you guys have a simple solution perhaps.

Currently, I feel like:

• I may be in Limp mode??
• High volume oil pump is causing me a headache by keeping the lifters pumped up. I did see an improvement adjusting the lifters and moving to a lighter weight oil.
• The ignition module may be faulty. Shouldn't the timing stay stuck @ the set point when the brown wire is disconnected?
• My valve lapping was not as awesome as I thought. I checked with alcohol at the time with good results. But then again, I may have inadvertently ingested some of the said alcohol at the time also......
• Perhaps the retard is due to the bog and I need to adjust the Fuel AE vs TPS somehow.?

Outside of that, I have a question regarding tuning once I get there.

• What are the major areas I need to be concerned with given my setup? Fuel obviously. What else?

Really appreciate your time. Hope all is well with the craziness out there these days. :yikes:

Jeremy

A few questions first,

Is the engine still on the test stand, or installed in the vehicle?
Is this a TBI conversion, or a factory installation?
Do you have a functional check engine light? Is it on? Any codes?

The ignition module does have some advance built in that will come into play when the ignition output is disconnected. If I'm not mistaken, the module also has some timing adjustments that will come into play even when the timing output is connected, that are compensated for in the PCM. There's a table in the PCM that should match the ignition module used. I believe that table is Spark Latency Correction vs RPM, if I remember correctly (I have the CRS and it's been a while since I played with TBI). Are you seeing the timing retard in your logs, or with a light? Monitor your spark advance in TunerPro and verify it with a timing light at various RPMs as a sanity check.

The PCM will adjust timing at idle to try to compensate for idle speed. You may have to adjust the Idle Overspeed and Underspeed tables to stabilize the idle.

Snapping the throttle at low RPM will result in low vacuum, which will result in very low spark advance. Look at your Main Spark Table vs MAP vs RPM tables. A lean bog will further reduce the vacuum. You'll probably need to adjust your AE vs MAP and AE vs TPS.

If you haven't already, set your Parameter Tree View to Parameter Category. This will sort your parameters into folders, making parameters much easier to find.

Regarding the high volume pump, the high oil pressure may be affecting the lifters. I would contact Lunati and get their thoughts on the oil pressure, and valve lash.

If the valve lapping is in question, I would recommend doing compression and leakdown tests.

I can't give much in the way of tuning advice. Perhaps some with more experience will chime in. Please upload your bin and a log for review.

you wont be able to tune out a mechanical problem. if your bearing clearances dont require it I would put in a standard volume standard pressure pump. if not you can supposedly run gallery plugs that limit flow to the rollers. quench doesnt mean much with dished pistons, you're just increasing your static compression. GM ran a 0.020" head gasket on the engines with dished pistons that i have seen. you need flat tops if you're worried about quench. i recently built a tbi headed (bowl cleanup) 355 w/ flat tops 0.035 quench. made 325fwhp and 420fwrq not bad for door stop heads. i havent towed with it yet but no detonation w/ shell 91 (no ethonol here in canada).

Thank you for the reply Neukam

There are some morsels in there I was hoping for that I can check out no problem. Very helpful. Glad to hear there is some timing built into the module. It was boggling my mind. Now I don't feel so bad. I thought about hooking up TP but I was frustrated and needed a break at the time. I am guessing if the brown wire is unplugged, the timing changes seen using the light at the balancer would not show up/match there anyway which would have been frustrating again. I decided to swallow my pride and reach out. Glad I did.

The engine is in the truck currently.
The TBI is native to the truck 93 GMC 5.7. Other than the serpentine pulleys, brackets and AC everything else has been replaced.

No check engine lights or logged codes currently. Initially I had the wrong knock sensor but once I procured and installed the correct unit, no codes other than the occasional CD42 from disconnecting the brown wire. This is the primary reason for thinking it is/could be mechanical in nature. No codes + engine funk usually means mechanical but my gut is saying it may be the tune since everything in the engine has been changed beyond what the computer is tuned for at the factory. Backfire at the exhaust could still be lean/timing related too. Just wasn't sure where to begin. I will check out the Main Spark Table vs MAP vs RPM tables and AE vs MAP / AE vs TPS. Hopefully it will net some improvement I can build on.

Now that I have had some time to contemplate, I don't know the HV oil pump is causing an issue. I ran the engine with the carb/HEI setup on the engine stand for 10+ hours over a few days and never had an issue even @ 3/4 turn. I'm thinking I may replace it anyway. I threw it in there on a whim and it hasn't set right with me since then. Just hate to mess with the seal etc. Dry as a bone currently but it is a reusable so I may just suck it up and make it happen later. Sooner if I can't make headway pretty quick. Clearances are pretty tight for sure.

I will upload a current log and the modified log once I get back out there to tinker again. The only log I have is pretty jacked up due to the CD43 I had because of the wrong knock sensor. The computer was intermittently adding 4 degrees of retard messing with any stable readings I thought I was seeing.

Thank you again for the advice. I will let you know how it goes.

Can anyone explain what Limp home symptoms are? I know it runs like crap but there must be some standard signs to look for. Possibly? Perhaps a quick-check like programming idle RPM? ....I just answered my own question didn't I?

Howdy tayto

Have to say I am impressed you got those numbers from the TBI heads. Everyone says they are good for torque but HP not so much. You obviously took the time to get it dialed in. Nice. I can appreciate the effort there. In fact, the reason I decided to use these heads was because of all the trash talk on other forums about 'how 305 heads are junk' for 350 use anyway. Well we will see I reckon. ;-P

Yes sir. That is the plan. Get everything mechanically sound then start the fun stuff tinkering.

Changing the oil pump is certainly logical. The more I think about it, the better it sounds although doing it in-vehicle kinda sucks. One thing I have going for me though is I took the time to open up the drain holes in the heads and lifter valleys while I had it apart. Seemed to be draining pretty good when I was adjusting the lifters but it was definitely getting lots of oil up there. I was thinking of possibly dropping in a set of Rhoads lifters instead. Maybe it will give all that oil something to do other than fill the rockers up? Any experience with that? I might give Rhoads a call.

I hear you on the squish. I was thinking the same initially. But guys smarter and more experienced than myself seem to believe it is still worth the effort as it does still force some turbulence toward the center of the piston and stave-off pre-detonation. A guy going by the name Grumpy had a pretty detailed write-up on TGO I really appreciated and there is some good information on some Harley sites as well.

Naturally when it comes to squish, flattop is better than dish. I really wanted a D shaped dish but didn't need to drop the cash for them. Seeing I was pretty hell bent on using these 305heads, I did the best I could while keeping the compression low enough to run on the street. A bigger cam could have allowed flat tops but, I had a cam. If I go for a new cam I am afraid things will get out of hand pretty quickly. IE. Bigger cam=why not roller=better make use of the cam=buy new aluminum heads=why not just go with tuned port etc and so-on. I just keep repeating to myself, Tinker Jeremy, Tinker and so far I have been good. So I made an effort and now have .050 squish with dished pistons. Better than nothing I think. It was easy to have the machine work done anyway.

Thank you for the reply!

Failsafe will cause a solid check engine light and run like dookie. Be sure to disable the checksum before emulating with the auto prom. If you don't you'll go into failsafe mode the first time you make a change. The larger cam will pull less vacuum, causing the engine to run rich at idle and low load. You're definitely going to have to work on your VE tables and spark tables. Installing a wideband will make dialing in the VE tables a lot easier. For AE, I'd start by adjusting AE vs MAP. You may not need to add much to AE vs TPS. If you don't need the high volume pump, it's probably better to put a standard one in. Less load on the distributor gear.

Hello Old Fart here. Back in the day grew up adjusting valves as part of Tune-ups. Before blameing anything else make sure the valves are correct. I suggest readjusting them here are a few hints. Usually chevy's were a 1/2 turn tighter after you loosen the rocker arm and hear the clacking. BUT that is not always the case. When tightening the lifter is pumped up and has to bleed out so 1/4 turn at a time until the engine shake stops, if it continues to shack(valve open) back off that's where lifter is happy. Another thought is connect a vacuum gauge to intake if the needle vibrates that's a leaking intake valve, wether to tight and slightly open or poor seat seal , worn guides. Also I would expect 14" to 18" of vacuum at idle with that cam you installed. Now for the next Rodeo, Timing. In your $OD BIN there is INITIAL TIMING in Scalars this is set to match your base timing that you adjust your distributor to. You need advanced base timing due to your camshaft to get the idle vacuum up preferably near 18" because your TBI is a Speed Density system and uses a Map sensor with TPS sensor and VE Tables to assume air volume. Next Scalar is MAIN SPARK BIAS, set it to Zero(0). Main spark bias lets the computer retard the timing as it sees fit. Now the engine will have an initial advance to work with the cam and it will work off the main and idle spark tables. That should get you further down the road. There is plenty more. Here is a Gift; https://www.gmcmi.com/wp-content/upl...EFI-System.pdf

Copy that Neukam

No check engine light is a good indicator the failsafe/Limp mode is NOT active.

Question on the AE vs MAP: Does a larger value = longer time-on for AE? That seems to be the case but I have not found any specific information confirming.

I need to invest in a wideband for certain.

Thank you for the reply,

Jeremy

Thank you for the reply Kilroy

Good call on the vacuum gauge. I may have time for that this evening. I think I have the valves set in their happy spot at the moment. Dad wore me out on adjusting them once-upon a time. In the 'if you want to drive, fix the car' phase of my life I got to fix lots of stuff. I wish I were half the mechanic really. Been a while though so I appreciate the support.

Reading through the document. Thank you. It will be a benefit for sure.

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Originally Posted by TBI Tinker

No check engine light is a good indicator the failsafe/Limp mode is NOT active.

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Yes. Be sure that the light is working during the lamp check sequence at key on engine off. If my memory is correct (no guaranties), the lamp should come on momentarily, then go off, then come back on and stay on until the engine is started. If the lamp comes on and stays on, without cycling off then back on, the ECM is in failsafe mode.

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Question on the AE vs MAP: Does a larger value = longer time-on for AE? That seems to be the case but I have not found any specific information confirming.

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I'm not sure if it affects AE duration, AE fuel quantity, or both. Larger value = more fuel. There are several thresholds and multipliers that come into play as well.

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Originally Posted by Neukam

Yes. Be sure that the light is working during the lamp check sequence at key on engine off. If my memory is correct (no guaranties), the lamp should come on momentarily, then go off, then come back on and stay on until the engine is started. If the lamp comes on and stays on, without cycling off then back on, the ECM is in failsafe mode.

Yes sir. Light is good for certain.


I'm not sure if it affects AE duration, AE fuel quantity, or both. Larger value = more fuel. There are several thresholds and multipliers that come into play as well.

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Copy that. I increased the values by 5% last night and it smoothed out some. Throttle is better but will still bog/die if pushed too hard. Exhaust backfire seems to be gone though. I will tinker with it more this evening. I also smoothed the Main Spark Table vs MAP vs RPM table per Eagle Marks tutorial which may have contributed some but I suspect the AE increase made the biggest difference.

I'm glad you're making progress. It's best to make changes to one thing at a time, when possible. Save a new bin with each change and keep notes. Focus on one area of operation at a time, like idle, then light load, etc. As you move to different areas of the map, you'll see trends that will give you an indication of what adjustments will need to be made. Keep at it and I'm sure you'll have it running good real soon.

I'd like to add some information that could be helpful.

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When the brown wire is disconnected at idle, timing is stable minus the slight retard seen [at the balancer] when the exhaust backfires.
As I increase the RPM to 1500 or so, the timing jumps an additional 7adv and stays there regardless of increasing/decreasing RPM. It immediately drops back to the set point once back under 1500rpm.

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Early TBI systems were designed with a number of redundancies. One of these is found in the ignition module. If the module is not in EST mode then it will very quickly ramp up spark advance when RPM reaches a threshold. There are different advance amount and different rpm thresholds based on the module part number, but most of the behavior described above should be considered normal. What is not normal imo is the report that spark advance changes during backfire. Unless this is happening at the rpm threshold mentioned above, I would be tempted to investigate the aftermarket ignition parts. Is the rapid change you described what you were referring to by "jumping?"

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If I'm not mistaken, the module also has some timing adjustments that will come into play even when the timing output is connected, that are compensated for in the PCM. There's a table in the PCM that should match the ignition module used. I believe that table is Spark Latency Correction vs RPM, if I remember correctly (I have the CRS and it's been a while since I played with TBI).

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In a factory stock application, the distributor generally delivers a reference pulse to the ecm when the crankshaft is between 0 and 10 degrees BTDC. In order to deliver spark to the engine up to 45 degrees advanced the ECM will use the incoming reference pulse to start a timer. The timer counts down the correct time to deliver a pulse back to the distributor to create spark at the desired crank angle. In order to deliver spark at the correct angle the ecm must know the distributor installed angle, the number of cylinders, the time between reference pulses, and the amount of delay, if any, that occurs between the ecm commanding "make spark now" and the plug actually delivering spark. Spark latency corrections account for the delay.

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If my memory is correct (no guaranties), the lamp should come on momentarily, then go off, then come back on and stay on until the engine is started. If the lamp comes on and stays on, without cycling off then back on, the ECM is in failsafe mode.

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Your memory is correct. At key on the ecm will attempt to ensure the data and program in the chip is not corrupt. CEL should light for a few seconds, go out for a few seconds, then light and stay lit. This will only happen if the key has been for for several seconds. The manual usually says 15 seconds but I've found it better to leave the key off for 30 or more before performing this test. If this cycle does not occur, if the light stays out or does not turn on - off - on, or if it flickers rapidly or blinks regularly, there's a high likelihood the ecm will begin operating in backup fueling mode.

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Question on the AE vs MAP: Does a larger value = longer time-on for AE? That seems to be the case but I have not found any specific information confirming.

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Performer style square bore dual plane manifold made by Dart

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The values in this table represent injector "on" time. Larger values turn the injector on for a longer time, delivering more fuel. That engine will want much more fuel during acceleration enrichment than a stock TBI. I expect you will be working on the VE tables considerably as well. If you have dyno software or a simulation for your engine you may save time using the shape of the torque curve to rough out the shape of your VE tables.

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A guy going by the name Grumpy had a pretty detailed write-up on TGO I really appreciated

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If that Grumpy is the same Grumpy I knew, he was a very creative thinker with many good posts. If you can find some of the early ones they are likely to get you thinking about EFI and engines in ways you hadn't previously.

1project2many brought out a thought about the ignition module. When they fail it's a no start, cuts off, or erratic engine operation. So you go to the local el-cheapo parts house and buy a new one, install and engine runs fine. A month or two later the same or similar problem starts. Your in denial because it can't be that new ignition module. Eventually you succumb because by now you've changed the fuel pump, ignition coil, etc, it was the module. Buy AC Delco IMO, don't forget the heatsink paste.

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Originally Posted by Kilroy

1project2many brought out a thought about the ignition module. When they fail it's a no start, cuts off, or erratic engine operation. So you go to the local el-cheapo parts house and buy a new one, install and engine runs fine. A month or two later the same or similar problem starts. Your in denial because it can't be that new ignition module. Eventually you succumb because by now you've changed the fuel pump, ignition coil, etc, it was the module. Buy AC Delco IMO, don't forget the heatsink paste.

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Anti-seize works as an excellent thermal conductor...better than the white paste. The copper based anti-seize is even better.