I have a 91' TPI 5.7 and am wondering if the ESC Module or can go bad or intermittently cause timing to retard? If so is it located on the drivers side behind the brake booster?

 

As I recall the SD cars have the ESC (knock filter) built into the MEMCAL rather than the external ESC like the 7165 MAF cars.

I have not seen one "go bad" but I guess anything is possible. I imagine if it failed high then perhaps the ECM would interpret that as a constant detonation condition and would pull the max allowed timing and never give it back. You would need to do some data logging with the knock sensor unplugged to prove this. Seems unlikely though.

GD

 

Thanks. I'm down to the knock sensor and or ECM causing the issue.

 

You could disconnect the knock sensor and run it like that. May get an error code, but if the knock sensor is sending false signals to the ECM, you could potentially at least rule that out.

Should also check the distributor shaft for excessive end play.

 

How have you verified the timing is being retarded? Plenty of other things can cause retarded timing.

Is the base timing set correctly?
Has the knock sensor ever been replaced?
Was the knock sensor torqued properly?
Is the EST wire unplugged?
Any SES light?
Is the ESC module correct for the application?

ULTM8Z has a great point about the end play on the distributor. VERY few people check distributor end play, but it can have a large effect on timing.

 

Doubt the new distributor is wasted, I have seen the memcals knock filter go bad but very rare.
the est disconnected would cause retard but I’m sure it’s plugged in. Like mentioned jusconnect the knock sensor. If over sensitive replace measure ohms before reinstalling 3.9k is 100k it’s wrong many parts stores will sell you a incorrect one. Torque to 14ft lbs iirc.

 

No SES light, New Distributor, Plugs, Wires, Ignition Coil, MAP, IAC, TPS. Car starts idles great, take off and it has a slight miss that cuts into the performance. Base timing is 6-8* with the EST disconnected. Connected the timing mark disappears or is way above 12*, almost 12 o'clock on the harmonic balancer if looking at where the mark is. It idles like a brand new car, the issue developed over time. I found that the distributor came loose and worked its way (retarded) and that resolved the almost not running and quitting/stalling issue.

I was wondering if the the pickup coil in the new dizzy got fried somehow from such a load being placed on the system when the ignition was retarded, two of the plugs had insulation glazing on them (#8 being blistered), so I replaced the ones that looked bad, the rest looked great.

It seems like when the EST is disconnected the car runs better, but it's hard to tell because when I test drive it is still down on power because there is no advance without the EST connected. I'm thinking the only things I haven't replaced are the KS and ECM. Fuel pressure and injectors are all good. 17 ohms on all injectors, and 45 psi when driving and giving it the gas...idle is like 38 psi.

Thanks for all of the help guys!

 

The problem with measuring spark advance in your drive way with EST connected and reving the engine is that the ECM is constantly varying it with RPM and MAP. You don't know what MAP/RPM you're at to compare your observation against.

So what you can do is disconnect the MAP sensor vacuum line (leave the sensor electrically plugged in ), the ECM would think you're at 100 kPa manifold pressure. Idle quality would probably not be too good... but...

Looking at the factory spark curve for an AUJP car, it's nearly a uniform 20 deg BTDC value across the entire RPM range. Now, if you rev the engine up a little and (if you have dial back timing light) you can check the timing at higher RPMs. It should stay between 18 and 20 deg. If you see it start bouncing around significantly, it'll tell you have some sort of spark control problem. At that point, disconnect the knock sensor and re-run the test. Could help you isolate the issue...

You shouldn't be triggering the WOT spark adder unless you get over 50% TPS. So open the throttle gently...

 

When I disconnected the vacuum line to the MAP previously, it will start and idle, but when I put it in Reverse and try and move the car died. I haven't tried that with the new MAP sensor though.

 

Lets back up here - have you confirmed with a timing light that the timing matches what the ECM is asking it to be? If you do not have the capability to do this, then STOP and get an ALDL cable or a scan tool that can tell you what's going on. This will also tell you if it's registering knock events.

And what exactly is the underlying symptom you are attempting to address here?

GD

 

That's what I'm trying to address with this test. By locking him into the 100kPa section of the spark table, the spark only varies by RPM, and the table has all RPM rows in the table between 18 and 20 BTDC in the 100kPa table.

So it's a "poor man's" way of doing it in your driveway without a scan tool. Just need a dial back timing light. Don't even need to know engine RPM really... it should stay at ~20.

BUT!.... you need to make sure base timing is set at 6 BTDC with EST connector disconnected. Should also be fully warmed up so you're out of the coolant correction bias table.

 

You do the test in park/neutral.

 

So I replaced the the knock sensor and it seamed a little better but it was most likely just wishful thinking on my part. Although it was not an end play issue with the Dizzy as it was only 8 months old. I did comment on the another thread that I thought the dizzy could still be the problem. So I took a chance and went to NAPA and purchased a remanufactured Cardone Dizzy (doesn't include cap and rotor). I installed the new reman dizzy and re-timed the car and it runs great again no misfire. So it must have been the pick up coil in the Autozone Dizzy that went bad, perhaps from when it loosened up and retarded to 4 ATDC it burnt up. I did compare the way the NAPA reman dizzy pick up coil and Autozone dizzy pick up coil rotated. The NAPA one has a little detent feel each time it goes past one of the poles when rotating. The Autozone one felt like it was making no connection. Luckily the Autozone Dizzy has a life time warranty on it, I returned if for a full refund. I will not buy any car parts there again accept for fluids, gloves, and tools.

I didn't expect a new dizzy to go bad in 8 months. The dizzy I took out was the original GM from 91' and the pick up coil was completely rusted as was the base...and it was still working when I took it out, it just looked bad and I was chasing down what ultimately was a bad ignition coil (said Made in China on the side), the one in there now is from Napa and made in Poland.

 

If you want a quality distributor, get one from Davis Unified Ignition. The parts store units, and the Amazon and Ebay units seem to last about 6-9 months and take a dump.

GD

 

Thanks I am going to remember it as DUI like I think you mentioned on another post. I will save it for my 355cid or 383cid HSR/AFR build. Will use this reman for now and save the higher end stuff for the higher performance motor. Then will drive up to Portland and have you tune it. :-)

 

Sweet! Bring it on up!

Rick

 

Car is still missing. So still convinced it was timing I unplugged the EST again to see if it was something related to the ignition, thinking perhaps ECM, but it didn't make any difference. For ***** and giggles I unplugged the 02 sensor and the car runs great in Open Loop...so with the O2 connected in Closed Loop there is a problem apparently. Guessing a bad O2 sensor? Perhaps when the timing was retarded it burnt out the sensor?

 

If the o2 wasn’t active you wouldn’t have closed loop. Btw what injectors did you install awhile back?

 

Right but with the O2 connected in closed loop the car misfires and gas mileage is very poor. I haven't driving it too much with the O2 disconnected approximately 8 miles to test it, and the car ran pretty damn good pulling the hill in OD trying to lug it, normal cruise, and WOT...didn't miss at all. As for the injectors last summer I had two issues going on. One was an intermittent failing ignition coil and the other was a weak alternator, both causing the car to die randomly one while driving the other while putting into gear/idling and the RPMS just dropped. I had originally thought it was the fuel injectors and replaced the Delphi injectors with Bosch, but after I think you and GD saying they had a little different voltages then the OEM, I put back in the Delphi's just to be OEM as I was having the problem with both sets of injectors (the Bosch ran fine too when the car ran). The car ran great for 6 months or so until this December when the dizzy hold down apparently came loose and the timing back off to 4* ATDC. I reset the timing and thought I had the dizzy worked out, but then it was missing bad. Since I replaced the 02 sensor last summer also I thought it was OK. But now I disconnect the O2 and the car is back to normal. I purchased a NOS Bosch MAP sensor I found on EBay just to rule that out. I think when the timing was so retarded that it could have screwed up the new 02 sensor???

 

You could replace the O2 I suppose. I'd get a Delco though... sometimes these aftermarket ones can be hit and miss. Unless you still have your old O2 sensor, you could plug that back in and see if anything changes.

But aside from that (and assuming the O2 sensor doesn't fix the issue) it seems you're replaced everything on the fuel and spark side to no avail. The other necessary thing for combustion is obviously compression.

May want to start thinking about a compression and leak down test. Since you're saying the car runs decent in open loop (and assuming again that the O2 sensor is ok), I'd focus on the driver side of the engine since that's the side with the O2 sensor and thus the only side the ECM can see and react to.

When you have a misbehaving cylinder on the driver side, it can cause the entire engine to run lousy because the ECM will add or subtract fuel on a "global" basis. So essentially the bad cylinder takes down the entire engine.

 

I was thinking a compression check was about in order next, but I haven't noticed any coolant in the oil, oil in the coolant, or any smoke of any color other than the normal morning condensation burn off while warming up, no coolant loss either.

So here is the funny but frustrating update. I took out the O2 sensor I took out last summer, and installed the old O2 sensor. I kept/keep any parts/sensors I swap out with new ones that don't fix the issues. After swapping in the old O2 sensor I took the car for a short drive and it didn't seem to fix anything. I finally decided to throw in the towel and take the car to a shop that has all of the scan gear and a guy on this board that was recommended in Sacramento for working on Thirdgens. His shop is about 40 miles away from me, as I drove down there I got to a road with about ten stop signs and signals. As I stopped at each one and took off there was no misfire, I thought to myself are you kidding, figures I decide to take the car to a shop and the issue disappears...classic. But I went ahead and dropped the car off and about 3 hours later I get a call from the shop saying that they put the car on the dyno with a 20hp load and the car doesn't miss and runs fantastic. Not sure if the ECM relearned something after installing the old O2, but I told him I had it unplugged the O2 last night and the car noticeably ran good/better, so I reinstalled the old O2 sensor at 6:30 this morning and it was missing and bucking when I took off out of my driveway so I figured there was still an issue. So something must have cleared up as a result or through a relearn of values as a result of new data from the sensor.

I have to admit I only have two OBD 1 vehicles a 94' Ford Bronco and a 91' Camaro, the others are either 60's or 2017 and newer, the OBD II stuff is easier to diagnose because I have a Bluetooth OBD II scanner that I can read on my Iphone...and so far it has been spot on with a couple of sensor issues I have had. I just use Chiltons and this board and the Bronco Forum for help mainly. So all of the info is appreciated.

On a side note, I see you are running the GV OD unit. I installed a GV on the end of my C4 transmission in my 66' Mustang. This allowed me to put 3.73:1 gears in the rear. Made a huge difference except now I can easily do 80 mph on the freeway at 3K rpms....which feels way to fast in traffic even with 4 wheel disc brakes. I dropped a 306cid AFR Heads and Cam motor in it and the sweet spot is really 3K rpms and above, so it get's on it on the freeway pretty good..things are just death traps..might as well be a Pinto or Corvair at that point.

 

There doesn't need to be coolant in the oil or vise versa to indicate a problem with compression. A blown head gasket can cause issues like that of course, but also failed piston rings, bad valves, etc.. The leak down test is also a good way to pinpoint where your problem is... rings? Intake valve? Exhaust valve?

Yeah, the GV is probably one of best mods I've ever done. Turned my TH700 into an 8 speed transmission. And with double overdrive I'm literally getting around 30 mpg highway with the highway mode fueling dialed in... ~2200 rpm at 85 mph in "8th gear".

~50 year old Camaro running ~30 year old engine technology getting ~30 mpg highway... crazy!

 

The ECM on these cars doesn't "learn" in the sense that you think. They start over from base settings on every power cycle. They only learn while running - nothing is stored between power cycles though.

When it does this is it still cold or do you warm it up? Could it be that the shop didn't experience the problem because it was warmed up when they dynoed it?

GD

 

I think the car was warm at the shop when they tested. When I was having the problem though (prior to swapping out the O2 sensor) it was missing no matter if it was cold, warm, or hot...didn't matter. Yesterday morning after I swapped out the O2 (it was low 40* outside), it was still not very warm maybe coolant temp 140* when I left down the street and seemed to be doing the same thing it had been doing, but then by time I drove to the shop it was at operating temp 212* or so and it was running great. Thanks for letting me know about the ECM learning, I thought maybe once it calibrated the idle BLMs and all that stuff it stored some basic info...didn't realize it was a reset every time the car is shut off and on.