Timing issues? 16197427 93 TBI

[Neukam]

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

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.

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'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.

[TBI Tinker]

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.

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.

[Neukam]

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.

[1project2many]

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

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.

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?"

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).

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.

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.

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.

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.

Performer style square bore dual plane manifold made by Dart

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.

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

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.

[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.

[Dieselsj]

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.

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

[TBI Tinker]

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

HA! Is there no end to the usefulness of copper anti-seize?!?

[TBI Tinker]

[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.]

Copy that. I am comfortable with this now and I do see the repeatability at the threshold rpm as would be expected.

[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?"]

Agreed and I plan to still investigate this weekend. The jumping I was referring to is related to the dip in timing at the time of backfire while the EST is disconnected and the erratic behavior while the EST is connected. Erratic being the not-so-consistent retard values when accelerating at idle. That being said, I have only watched the timing with a light and I have not looked at it since I bumped the AE vs MAP values and smoothed the spark table. The adjustment seemed to attenuate the exhaust backfire and smooth out the throttle some. BUT that was one 20 minute session. Just enough to warm up, tinker for a minute and shut down for dinner. Should have more time this weekend to validate the improvements. My gut tells me it is likely related to the tune at this point.

[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.]

Copy that. Matches up perfectly with what I had in mind.

[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.]

I like this plan a lot. Sadly, the last time I ran Desktop Dyno it was on a floppy drive. I have been thinking about procuring a copy of the new program though. I have about a bajillion dollars wrapped up in kids video games. What's wrong with a little fun for dad right? Meh. we'll see.....that first program was really helpful to me back in the day though.

[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.]

It may very well be. I have read his and others posts till my brain was smoking considering what to do with this engine. Very insightful and he was good with relaying that very technical information in layman's terms. With a huge amount of resources. Huge. Truly dedicated individual as far as I could tell. Sadly I never knew him. But what a wealth of information. For real. I work in a very technically oriented field and the only way I can decompress sometimes is to read about other very technical but unrelated information. This site and TGO has been great for me. Truly appreciated.