Lean Misfires at 2700-2800 rpm

[ProwlerGT]

Originally Posted by badass3000

all of last year I was too thinking something electrical, but after replacing every unit/plug/sensor that could be related I have to start looking somewhere else.

Bob, are you thinking that even though we have tried known good ECU's, that our ECUs are still faulty -or- perhaps receaving an improper signal causing faulty results?

ABSOLUTELY.

I have my own belief that ALL 1st GEN ECU's are not only trash, but also have a programming bug. I wouldn't put 1% faith in them at all. I would definitely do the idea of trying the AEM, but I know.... very expensive. Still its a small price to pay rather than spending one's ENTIRE LIFE trying to fix this car. BELIEVE ME - I KNOW HOW THAT IS! lol

If no go for a try with the AEM ECU - Have you tried new O2 sensors? Have you tried TESTING your O2 sensors "out of the car"? If you don't know how I'll dig up the test method I found somewhere.

[badass3000]

I hope your wrong about the 1st gen ECU's, b/c I dont want to use any other.
I love how they dont throw a CEL if you forget to buckle up.

O2 sensors? what are those? I have mine unhooked, trims at 100%, b/c if I want to run lean on the interstate for beter gas milage then I can.

[TurboBob]

Originally Posted by badass3000

all of last year I was too thinking something electrical, but after replacing every unit/plug/sensor that could be related I have to start looking somewhere else.

Bob, are you thinking that even though we have tried known good ECU's, that our ECUs are still faulty -or- perhaps receaving an improper signal causing faulty results?

I don't think they are 'faulty' or this would be fixable by swapping ECU's I thiink its related to the calibration on the stock vehicle. The stock vehicle was most likely programmed to comply with emissions regs below 2800 - 3000 and not above. Thus the abrupt switch. So below 2800, EGR is maxxed, and the tuning/calibration is optimized to run cleanly. This may make the car sensitive to old ignition coils, cold plugs, etc.

I have watched the scanmaster during this transition point and spark advance does not appear to change, but the datastream may not be fully accurate.......

running open loop thru this point seems to help. I just wonder if part of the transition is due to weak spark from low ignition dwell...

Bob

[DoctorDex]

Bob: I'll head back to the electronics place again and have the dwell tested. Another thing I'm going to do is try out your idea with the coolant resistor mod. I'm going to have them rig up a variable resistor (in line with my coolant sensor) so that way I can systematically "vary" the coolant temperature. Since this problem improves, to some degree, when the car is warm I think it'd be worthwhile to fool it into thinking it is only luke warm (120F to 165F) to see if the problem worsens. Then if the missing is unchanged, then this points to a mechanical cause.

Only problem is I don't have time to do this for at least a couple more weeks because of exams...

Edit: Anybody has an MSD-DIS4? I believe these units are supposed to increase dwell in the lower rpms.

[jwetzler]

Originally Posted by DoctorDex

Another thing I'm going to do is try out your idea with the coolant resistor mod. I'm going to have them rig up a variable resistor (in line with my coolant sensor) so that way I can systematically "vary" the coolant temperature. Since this problem improves, to some degree, when the car is warm I think it'd be worthwhile to fool it into thinking it is only luke warm (120F to 165F) to see if the problem worsens. Then if the missing is unchanged, then this points to a mechanical cause.

Edit: Anybody has an MSD-DIS4? I believe these units are supposed to increase dwell in the lower rpms.

I haven't been following this thread too much as of lately, so I dont know if this has already been covered...

Have you tried just unplugging your coolant sensor? When I got my tranny swapped out a long time ago, the guy forgot to plug in my coolant sensor.

The car still ran fine even though it had a CEL from it. I took it to my mechanic, and he said that when the coolant sensor is unplugged, it will feed the ECU a preset/default temperature so that the car will still run.

Just a thought, dont know if it will help or not. He had one of those big OBD1 code readers, and it gave him the actual default temp it would give to the ECU during that CEL. I just can't remember the exact temp. That was almost 3 years ago.

[DoctorDex]

When I unplug the coolant sensor the car will not stay running unless I keep my foot on the gas. IIRC, the temp it puts out is like -30F or something like that.

[ProwlerGT]

Originally Posted by TurboBob

I don't think they are 'faulty' or this would be fixable by swapping ECU's I thiink its related to the calibration on the stock vehicle. The stock vehicle was most likely programmed to comply with emissions regs below 2800 - 3000 and not above.

Swapping stock ECU's or swapping stock for a 3rd party ECU?

Are you saying you've swapped with a 3rd part ECU and that didn't fix it?

I can count on 1 hand how many people have told me their 1st gen ECU was in good shape and not causing them a problem. I don't believe in "known good stock ECUs" for 1st gens (at least at this date). I have seen/heard/read of too many bad ones and in some cases people replacing them 3 times over.

Regardless if its a calibration issue in the programming even if it was programmed to emissions regs it still amounts to a malfunction condition later on and shouldn't have been allowed in production no matter what the laws are.

Though what does of course come to mind is that 1st gens certainly did not always behave in this faulty manner when they were new to moderate in age. Unfortunately parts of electronics as well as mechanical parts both degenerate over time and perhaps even replacement electronic parts for these boards are also deteriorated and I'm only stating this with minimal electronics experience thinking that old boards need old parts.

Perhaps if one could determine what internal engine revisions may have been made from the 1st gens to 2nd gens a red flag may go off and I mean why do the 1st gens have this problem and 2nd gen's don't? If there were no internal engine changes aside from the lifter upgrades in 99 then I'd go back to what I've thought all along - electrical/board etc..

[TurboBob]

Originally Posted by DoctorDex

Bob: I'll head back to the electronics place again and have the dwell tested. Another thing I'm going to do is try out your idea with the coolant resistor mod. I'm going to have them rig up a variable resistor (in line with my coolant sensor) so that way I can systematically "vary" the coolant temperature. Since this problem improves, to some degree, when the car is warm I think it'd be worthwhile to fool it into thinking it is only luke warm (120F to 165F) to see if the problem worsens. Then if the missing is unchanged, then this points to a mechanical cause.

Only problem is I don't have time to do this for at least a couple more weeks because of exams...

Edit: Anybody has an MSD-DIS4? I believe these units are supposed to increase dwell in the lower rpms.

the MSDs are capacitive discharge, and therefore don't dwell.

That is a good question, the HKS DLi is another question. (I wonder whats in the HKS...)

Bob

[TurboBob]

Originally Posted by DoctorDex

When I unplug the coolant sensor the car will not stay running unless I keep my foot on the gas. IIRC, the temp it puts out is like -30F or something like that.

I will try this myself.

[DoctorDex]

Originally Posted by TurboBob

That is a good question, the HKS DLi is another question. (I wonder whats in the HKS...)

I have an HKS and I have no idea how it works. All I know is it doesn't do anything for this problem.