High RPM's on start up

[joshwilson3]

On my 1988 and 1989, you need a 10K resistor (pins 2 and 4) to flow ALDL data when using a home made serial cable. 3.9K enables factory test mode. 0K enables diagonostic mode (flash codes). Open mode did not work on ECM 1227165.

I ended up figuring out I needed to download some ECM definitions into the Tunerpro. I haven't tried it again yet. Didn't figure out why the Winaldl didn't work though, but I'll try the Tunerpro again.

The Moates cable does have the 10k resistor you can turn on and off.

 

[joshwilson3]

I've got some data logged. I don't really know what to look for. But I uploaded some snap shots of the scan. For the last several weeks, I've noticed the cold RPM spikes aren't as high as they were. I do notice sometimes on the warm RPM spike, that at the peak, I can hear something from the exhaust. It's not a pop, so I wouldn't think it was a back fire.

I highlighted the engine RPM and engine run time.

This is a cold start up. I did the snap shot at the RPM peak right before it went back down to 950 rpm cold idle a few seconds later:

Here is a warm start up. I did the snap shot at the RPM peak right before it went back down to the 750 rpm warm idle a few seconds later:

This is another snap shot from the same warm start up scan posted above, but is 3 seconds later:

 

[vetteboy86]

Your TPS is pretty much right on. The values are the same for the different RPM's. Take a look at your IAC steps. The steps for the high RPM's are considerably higher than when normal RPM's. I'm going to keep looking at the data. This is a good starting point!!

 

[TedC]

In the second set of results, RPM was 1925 with step 77 but the desired RPM was 775. ECM could not properly manage idle speed. Then in the third set of results, RPM was 750 with step 11 and the desired was 775. Looks like the ECM is now able to manage idle speed. Can you run another test with engine fully hot just prior to cooling fan enablement? Want to confirm step count which should be around 15. Does the Prom ID look strange to anyone else?

 

[joshwilson3]

In the second set of results, RPM was 1925 with step 77 but the desired RPM was 775. ECM could not properly manage idle speed. Then in the third set of results, RPM was 750 with step 11 and the desired was 775. Looks like the ECM is now able to manage idle speed. Can you run another test with engine fully hot just prior to cooling fan enablement? Want to confirm step count which should be around 15. Does the Prom ID look strange to anyone else?

So, you want me to get the temp to say 220. Shut it off. Then start it up while the scanner is going and post a snap shot of the max RPM value on cranking?

I believe with the key "on" the IAC steps start off at 160. Then when cranking they rapidly fall down to the 11 steps you saw a few seconds later.

I already tried grounding out the ALDL with the key "on" to extend the IAC pintle all the way out. Then start the car with the same RPM spike. I'm thinking maybe next time I could ground out the ALDL with the key "on". And then unplug the IAC, then start the car and see if the RPM spike is still there. As one theory was of an air leak that gets corrected by the IAC. But if the IAC is already fully extended on start up and I still get the RPM spike, then that should rule that out. But I believe if there was an air leak, I should also have an idle problem instead of just a starting RPM spike.

 

[TedC]

Why do you need to restart the engine? Run engine, listen for fan to kick in when hot, record and post results after the fan has shut off. Avoid any load from fans, A/C, or charging the battery which impacts the IAC steps. Interested in the desired speed, actual speed, and number of steps when hot. I have four concerns so far. They are; desired RPM when hot, IAC steps when hot, ECM's ability to manage actual RPM +/- 50 rpm, and the prom id which doesn't look right to me. Please confirm this is an automatic with stock eprom.

 

[joshwilson3]

Why do you need to restart the engine? Run engine, listen for fan to kick in when hot, record and post results after the fan has shut off. Avoid any load from fans, A/C, or charging the battery which impacts the IAC steps. Interested in the desired speed, actual speed, and number of steps when hot. I have four concerns so far. They are; desired RPM when hot, IAC steps when hot, ECM's ability to manage actual RPM +/- 50 rpm, and the prom id which doesn't look right to me. Please confirm this is an automatic with stock eprom.

It is an automatic. I'm guessing it is the stock eprom as I've never messed with it.

The idle flickered between 725, 750, and 775:

Looks like the desired RPM is 625, but actual RPM is 750 with the ECM commanding the IAC to the fully closed position.

Since I've got the scanner, I probably do need to check/set the min air. As that is the one thing I couldn't do before when I set the TPS.

 

[TedC]

A few observations.

1. TPS voltage is slightly off but within acceptable specifications. You can use this setup to adjust properly to what the ECM reflects. You want .54V at idle position and 4.3V+ at WOT (gas pedal) with key on and engine not running. If you play with the TPS position you may be lucky and reach 4.5V+ at WOT. The maximium reference voltage is 5V. (LOW PRIORITY)

2. Your BLM (Block Lean Multiply) at 117 which indicates your engine is running rich. 128 +/-2 is the target range. Read this to better understand the terms ECM Tuning - GM Wiki . Also, your INT is 126 which is also showing a rich condition. Fully hot, the L98s I've worked on always posted a 128 INT unless the fuel injectors were messed up. (HIGH PRIORITY)

3. O2 sensor is also posting a rich condition at .7V. Again, this should not be happening with a fully hot engine. This reading can bounce around some, but the INT and BLM are indicating short and long term rich conditions. The injector pulse rate is low which also indicates the injectors are flowing more fuel than required and the ECM is reducing the duration of pulse time to reduce flow rate. (HIGH PRIORITY)

4. IAC step of 0 with 750 RPM vs. desired of 625. The ECM tried to manage idle and fully closed the IAC. This indicates air is getting into the intake above the TPI design point. (HIGH PRIORITY)

Amazing what data you can collect with a scanner. My suggestions.
1. Investigate and confirm PROM ID for the being the right one.
2. Investigate the type of injectors you have and if they are stock flow rates.
3. Measure each injector for resistance. Should all be around 16 ohms.
4. Check for intake leaks around gaskets, TB, injector o rings, and brake booster.
5. Check timing, min air speed, and reset TPS as required.
6. Reset ECM and recheck results after you drive it around.

 

[joshwilson3]

A few observations.

1. TPS voltage is slightly off but within acceptable specifications. You can use this setup to adjust properly to what the ECM reflects. You want .54V at idle position and 4.3V+ at WOT (gas pedal) with key on and engine not running. If you play with the TPS position you may be lucky and reach 4.5V+ at WOT. The maximium reference voltage is 5V. (LOW PRIORITY)

2. Your BLM (Block Lean Multiply) at 117 which indicates your engine is running rich. 128 +/-2 is the target range. Read this to better understand the terms ECM Tuning - GM Wiki . Also, your INT is 126 which is also showing a rich condition. Fully hot, the L98s I've worked on always posted a 128 INT unless the fuel injectors were messed up. (HIGH PRIORITY)

3. O2 sensor is also posting a rich condition at .7V. Again, this should not be happening with a fully hot engine. This reading can bounce around some, but the INT and BLM are indicating short and long term rich conditions. The injector pulse rate is low which also indicates the injectors are flowing more fuel than required and the ECM is reducing the duration of pulse time to reduce flow rate. (HIGH PRIORITY)

4. IAC step of 0 with 750 RPM vs. desired of 625. The ECM tried to manage idle and fully closed the IAC. This indicates air is getting into the intake above the TPI design point. (HIGH PRIORITY)

Amazing what data you can collect with a scanner. My suggestions.
1. Investigate and confirm PROM ID for the being the right one.
2. Investigate the type of injectors you have and if they are stock flow rates.
3. Measure each injector for resistance. Should all be around 16 ohms.
4. Check for intake leaks around gaskets, TB, injector o rings, and brake booster.
5. Check timing, min air speed, and reset TPS as required.
6. Reset ECM and recheck results after you drive it around.

Yeah, when I set that TPS last, it was dead on .54. But I guess driving around moved it a hair.

It has been running rich for a while from the old plugs the PO gave me and from the plugs I pulled. The PO replaced the injectors with Accel 24# injectors, then the FPR to fix a miss. I know the injectors should be 22#. But it might of been running rich before the new injectors were installed since the PO gave me some old plugs. Could of been cause the FPR was bad. They did ohm okay last I checked them both cold and warm.

On the O2 sensor. That number usually changes like 10 times a second. It goes up and down real fast. The number does change to red some I guess when it goes down too low or goes too high.

How do you check injector o rings for air leaks?

The timing is dead on 6* advance. I'll need to check/set the min air then of course reset the TPS. I know the min air has been messed with as that plate is missing.

 

[TedC]

I like things exact. So .5400000000V for me. Once set, it shouldn't change much unless there is play in the throttle shafts or they are binding. I can't provide much advice on those 24# injectors. They are too large for a stock L98 unless you reprogram the eprom. I would trash them and install a set of Bosch IIIs from FIC. You can use WD40 around the o-rings to see if it changes idle speed.

 

[joshwilson3]

I like things exact. So .5400000000V for me. Once set, it shouldn't change much unless there is play in the throttle shafts or they are binding. I can't provide much advice on those 24# injectors. They are two large for a stock L98 unless you reprogram the eprom. I would trash them and install a set of Bosch IIIs from FIC. You can use WD40 around the o-rings to see if it changes idle speed.

The injectors have been on there for 6 years or so. I'm just gonna leave them.

When you do the WD40 trick and if it changes idle speed. Does it raise it or lower it?

 

[boomdriver]

The injectors have been on there for 6 years or so. I'm just gonna leave them.

When you do the WD40 trick and if it changes idle speed. Does it raise it or lower it?

you hear it...

 

[vetteboy86]

In closed loop, your O2 sensor should bounce back and forth from 0 to 1V, or there about. The fact that you have taken a snap shot with an 02 reading of .7 volts is coincidence. I definitely think you can fix your rich condition.

If your setup for tuning, you can easily change the injector constant from 22lb to 24 and see how that effects your rich condition.

 

[joshwilson3]

In closed loop, your O2 sensor should bounce back and forth from 0 to 1V, or there about. The fact that you have taken a snap shot with an 02 reading of .7 volts is coincidence. I definitely think you can fix your rich condition.

If your setup for tuning, you can easily change the injector constant from 22lb to 24 and see how that effects your rich condition.

I'm not setup for tuning. I assume that means getting a new chip burned?

 

[boomdriver]

In closed loop, your O2 sensor should bounce back and forth from 0 to 1V, or there about. The fact that you have taken a snap shot with an 02 reading of .7 volts is coincidence. I definitely think you can fix your rich condition.

If your setup for tuning, you can easily change the injector constant from 22lb to 24 and see how that effects your rich condition.

he can also drop the fuel pressure from 43 lbs to around 30-35lbs.
Thats the difference between 22 lb/hr and 24 lb/hr injectors.
About 8-10 psi of fuel pressure.

35 psi fuel pressure is plenty for atomization and that will help eliminate the multiple "rich" conditions that are seen in the scans. The ECM is possibly trying to adjust the ratios as if there were a condition to be met when in fact the 24 lb inj are simply adding more fuel for the set pulse-width.. If its been running a little rich then there ARE definately fouled plugs. The spark plugs should be burning tan to off-white in color. Any darker is not good.

For a stock motor its best to stay as stock as possible. One thing like bigger injectors throws everything else off.

 

[joshwilson3]

he can also drop the fuel pressure from 43 lbs to around 30-35lbs.
Thats the difference between 22 lb/hr and 24 lb/hr injectors.
About 8-10 psi of fuel pressure.

35 psi fuel pressure is plenty for atomization and that will help eliminate the multiple "rich" conditions that are seen in the scans. The ECM is possibly trying to adjust the ratios as if there were a condition to be met when in fact the 24 lb inj are simply adding more fuel for the set pulse-width.. If its been running a little rich then there ARE definately fouled plugs. The spark plugs should be burning tan to off-white in color. Any darker is not good.

For a stock motor its best to stay as stock as possible. One thing like bigger injectors throws everything else off.

Last I checked, fuel pressure was at 34 lbs.

Yes, the plugs the PO gave me, and the plugs I pulled a year ago were carbon fouled. But I'm not sure if the carbon fouled plugs the PO gave me were pulled before or after he put in new injectors. Driving around with my scanner, I do see if flopping back and forth between lean and rich. So, maybe the rich condition isn't constant.

Yup, sure does suck that Accel markets these as a stock replacement when they are not.

 

[joshwilson3]

Anyone ever rigged up a smoke machine, or converted a smoke/fog machine to pump into the booster line?

I've read of some home made smoke machines that uses a glow plug, baby oil, and an air compressor. I'm thinking an air compressor would work better than a fog machine, as you can control the PSI.

I've read you pump the smoke at like 2-3 PSI into the booster line with the engine off. Then look for smoke.

 

[TedC]

If you plan on keeping 24# injectors then get a new chip burned. Reducing fuel pressure kills performance and is a poor bandaid. The stock eprom is set for 22# injectors. You can see by the results posted that the BLM is way off. Reducing fuel pressure helps but it can't totally resolve the mismatch. Will continue to run rich in open loop and power enrichment. The spark plugs are saying "HELP ME", and this condition is screwing up the converters, o2 sensor, EGR, and intake with carbon. I would avoid other adjustments like min air speed until this is resolved. Talk to Jon at FIC. L98s respond extremely well to fuel atomization, and the Accel spray pattern was tested to be worse that the stock injectors using stock fuel pressures.

 

[joshwilson3]

If you plan on keeping 24# injectors then get a new chip burned. Reducing fuel pressure kills performance and is a poor bandaid. The stock eprom is set for 22# injectors. You can see by the results posted that the BLM is way off. Reducing fuel pressure helps but it can't totally resolve the mismatch. Will continue to run rich in open loop and power enrichment. The spark plugs are saying "HELP ME", and this condition is screwing up the converters, o2 sensor, EGR, and intake with carbon. I would avoid other adjustments like min air speed until this is resolved. Talk to Jon at FIC. L98s respond extremely well to fuel atomization, and the Accel spray pattern was tested to be worse that the stock injectors using stock fuel pressures.

The fuel pressure is already at the bottom anyway of 34 lbs last I checked.

I'm gonna go ahead and check/set min air as that is really the last check I can think of I haven't done yet and figure out on the RPM high rev on start up if that doesn't fix it.

Yes, it would be a good idea to replace the injectors. But that's like around $200 if I do it. I planned to quite spending money on it a year ago but I keep finding things to do some of which I'm not gonna mess with unless I have to. So, maybe next year some time.

 

[TedC]

If you plan on checking and adjusting min air speed knowing your situation, you will want to push up the IAC counts by backing out the idle screw. Just be careful that you don't fully seat the throttle plates. The screw tip is the right stop point, not the throttle plates in the bores. I suspect you will need to close the plates more than that required with the proper injectors. Good luck, and keep us posted on the results.