Dave's Winter 88 Behaving Badly

[2seater]

I am posting on Daves behalf because this one is a head scratcher, maybe. The story starts with the winter car, an '88 with a bit of over 200k miles. Per phone conversations, recently noticed an apparent severe misfire under load when pushed to higher power levels. Starts and runs at low speed just fine. Due to Dave's vast inventory, replaced the Delco coils, then the whole module assembly and finally a good running Magnavox set from his convertible. No apparent improvement, and maybe getting worse. I suggested watching the diagnostics for knock counts and spark retard, TPS values for odd dropouts, spark timing, etc... but some of the numbers coming back were way out in left field. More on that in a bit. He also has a good Snap On fuel pressure gauge with a long hose so it could be observed while driving. All appeared normal, 42psi key on, 36psi idling, blip throttle and jumps over 40, same for driving.

 

Fast forward a few days and I stopped over to see if anything jumped out at me. The engine starts quickly and idles well. Engine is quiet mechanically. I installed six spark testers to allow watching the spark from all at the same time. There is a Delco set in place, new plug wires, and routing triple checked. Spark looks good, so revved the engine in park and can now make the engine misfire or whatever it is, simply by increasing rpm to a higher level. I don't know how high, but guessing 3000rpm, and it starts to pop and bang. Occasional backfire through the intake. Fuel pressure remains good while this happens. Unplugged the MAF, no difference. I put it in diagnostics to see if anything showed up there when I noticed the text labeling for some of the ECM Data items are incorrect, either out of place or not from the ECM Data at all, six or seven of them in total. It explained why the numbers Dave was giving me over the phone were so out of whack. I am more used to the late style diagnostic system that has no real text involved just the ED#. Once I figured out the displayed label was incorrect and just used the item number, diagnostic readings all fell into place. Everything appears completely normal, even when the engine starts to buck and bang. Timing remains steady, MAF, TPS, O2 sensor all stay where they should be even with the engine misbehaving. Even the knock counts don't go crazy. The only small item is the Block Learn is almost pegged at 150-155 at higher rpm, indicating it is adding fuel but the integrator is reading right around 128 so it is doing its job.

 

Overall, the exhaust smells on the rich side, but I am thinking it is a symptom, not a cause. It sounds for all the world like an old SBC that has lost one or more cam lobes and I had more than one in my Chevy days. Low speed and idle are okay but revved up, it backfires through the intake. Actually I had that happen on a Ford Taurus 3.0V6 also, and I replaced the cam in that one twice. Those were flat tappet engines but ours is a hydraulic roller, much less prone to wear. I do have one of ours on my shelf with unknown mileage, with one lobe worn substantially, so it can happen. From what Dave has mentioned, it seems to be getting worse, or more sensitive when warm, but is less prone to misbehave when cold and open loop. He reports this car doesn't do as good of mileage as his others, and never has. This engine has had the timing set, crank and cam sensor, intake manifold gaskets and O2 sensor replaced approx. 17k miles ago. The final thought is the odd and incorrect information on the CRT while in diagnostics. I don't know where that information comes from, but it does make me question of the ECM is correct for this car??

 

Sure could use some suggestions

[Ronnie]

2 hours ago, 2seater said:

Spark looks good, so revved the engine in park and can now make the engine misfire or whatever it is, simply by increasing rpm to a higher level. I don't know how high, but guessing 3000rpm, and it starts to pop and bang. Occasional backfire through the intake.

This makes me think maybe a broken outer valve spring since it seems to be RPM dependent and not caused by just a heavy load on the engine.

[Ronnie]

3 hours ago, 2seater said:

The final thought is the odd and incorrect information on the CRT while in diagnostics. I don't know where that information comes from, but it does make me question of the ECM is correct for this car??

Maybe the ECM is bad and causing the problem. Swapping it out should be an easy test. I think the BCM would be responsible for displaying information on the CRT. Don't know that. Just guessing.

[DAVES89]

Thanks guys. Before I start anything I want to wait for input from Padgett who probably has the most knowledge of the ECM and BCM capabilities.

 I know that at least in October I was doing hard accelerations through the back end of the church's parking lot on my way to the power equipment to cut grass...

[Padgett]

I remember a TSB about some defective cams in that era but have never experienced it (never had an 89 either). Computers rarely fail a little. Would check trims, CPS,TPS, MAF, O2 first. Torque Pro can display many parameters at once. Mechanical things do not heal.

[DAVES89]

This is a 1988 with 205,000 miles

I'm assuming you mean:

CPS=Crank Position Sensor not "Central Power Supply"

TPS=Throttle Position Sensor

 MAF= Mass Air Flow Sensor

TPS reads within specs

O2 Sensor light "blinks" on touch screen, but have a new one in parts bin

 Swapped in a different MAF no change. Disconnected it no difference

 I suggested to 2seater maybe Crank Sensor Have a new one in the parts bin.

Edited December 13, 2021 by DAVES89

[2seater]

I mentioned at the time that I wish I had brought a vacuum gauge. Can sometimes find a weak cylinder through regular vacuum drop while running. I noted that at least one time when it did the intake backfire we saw a puff of smoke from the area between the throttle body and EGR but it didn't seem to be something we could get to repeat. Investigating the area didn't turn up anything obvious. One other probably unrelated item is the throttle would stick partially open. It would snap back if the throttle was blipped but a steady increase in pressure on the throttle would hold it right where it was. Spraying lube on the linkage and springs on top of the TB appeared to have corrected that but it is something I have never seen before. I thought perhaps a worn spot on the throttle blade shaft but it all appears nice and tight.

 

We did watch each sensor in turn and then increased rpm to get it to misbehave and the sensor readings remained steady, which seems to indicate a mechanical rather than electronic problem. While our onboard diagnostics are nice, they do have a lag time and aren't designed to give the same resolution as an o'scope, but should have shown something when held for several seconds. Dave suggested a failing CPS and I have learned to never say never. I had one several years ago that defied the normal failure mode and would heal repeatedly, so as time and age marches on, new and different failures pop up.

[Ronnie]

52 minutes ago, DAVES89 said:

O2 Sensor light "blinks" on touch screen, but have a new one in parts bin

That indicates it is in closed loop. Does the problem start happening even before going into closed loop?

[2seater]

3 hours ago, Padgett said:

I remember a TSB about some defective cams in that era but have never experienced it (never had an 89 either). Computers rarely fail a little. Would check trims, CPS,TPS, MAF, O2 first. Torque Pro can display many parameters at once. Mechanical things do not heal.

This isn't Daves signature vehicle, it is an '88, probably an early one with suede bolsters. This was Vincent Vega's car. 

[DAVES89]

4 hours ago, Ronnie said:

That indicates it is in closed loop. Does the problem start happening even before going into closed loop?

No. When the car is cold [before closed loop] it runs great. In closed loop is when it starts acting up.

[DAVES89]

1 hour ago, 2seater said:

This isn't Daves signature vehicle, it is an '88, probably an early one with suede bolsters. This was Vincent Vega's car. 

Yes it was Vincent's car and it was an early '88 with the suede bolster seats and brown horn button. Both replaced with sunburst horn button and 16 way passenger seats [to protect the 16 way suede from wearing out too quickly.

[Ronnie]

17 minutes ago, DAVES89 said:

No. When the car is cold [before closed loop] it runs great. In closed loop is when it starts acting up.

I would disconnect the O2 sensor wire  to make it stay in open loop and drive it around like that for a while and see if the problem comes back. The check engine light will be on but is should still run decent. If the problem doesn't come back with the O2 disconnected you can be pretty certain it's not an ignition problem or a mechanical problem.

[DAVES89]

Ronnie, that is a great idea. If it works I'll try to get you a raise as a troubleshooter on this Reatta Forum as I am on good terms with the Moderator. I am really sure it is not a mechanical issue as it would do it all the time. I'm leaning towards the 02 sensor or crank sensor with the ECM last. I remember years ago there were a couple of guys that were having ignition/driving issues and it was suggested that they remove the ECM from it's mounting position and leave it laying on the carpet as it might have a short or overheats after running the car. If it ultimately turns out to be a "silver box" I believe it will be the first one I will have ever replaced. And that covers 4 cars and combined miles of over 900,000 [not all miles by me].

 

Edited December 14, 2021 by DAVES89

[DAVES89]

I disconnected the 02 sensor and the service engine soon light did not come on. I let it get to operating temperature and the bucking is still there, but it seemed like I could give it more gas. 

I find it hard to believe that it is a mechanical issue as I would think that it would do it all the time and not just when it is warm. 

[Ronnie]

I think that test proved the O2 sensor isn't the problem. Did the bucking start just as the engine reached operating temperature and run fine while cold or did it start gradually as the engine temperature was going up?

[DAVES89]

It ran fine cold, but then at about 140 degrees I pulled over and let it warm up to about 166 degrees [where if the 02 sensor was connected it would go into closed loop] where it "sat" for a bit and didn't seem to want to move until I started driving it. The temperature then started moving up to full operating temperature but the bucking was there [from 166 on up].

[DAVES89]

I just checked my parts bin and Vincent had replaced the ECM once before as there is one in a box with a Parts House receipt from Madison. I do have two others, one is a facory rebuild, the other is one from a good running car I parted out. It also has a "ASSUE" prom in it which I wrote on it that is a desirable prom.

[Ronnie]

This is a brain twister.  I would check and see what codes you have after driving with the O2 sensor unplugged. The only other thing I know that happens when the temp hits about 160* is the ECM will allow the the torque converter to lock when conditions are right. On my car this can happen just before the engine temp gets high enough to go into closed loop. You could disconnect the electrical connector from the transmission and drive to see if that makes a difference in the bucking. I doubt it will but it's worth trying and swapping the ECM is worth trying to see what happens. Changing the crank sensor is an option to but it would be really odd that it started giving a problem at the exact time the ECM goes into closed loop. Other than that right now I'm stumped.

[2seater]

I agree with Ronnie, it does make your brain hurt. I just looked at the PROM list in the how to guide and it appears ASSU is for 1989. I don't know that it is substantially different than the 88's, but ??? Generally the alphabetic listing moves from left to right in the alphabet order as time moved forward. I have no idea really and hope Padgett can shed some light on the subject. Maybe it will explain incorrect text for the diagnostic readout, even some from the BCM which don't belong at all. I agree that if it behaves cold, but not warm, a mechanical fault seems less likely. Open loop it runs on the preprogrammed information in the PROM, which is designed with "safe" parameters in mind, so it would be nice if there was a simple way to shift it in and out of loop so as to narrow the focus. 

[DAVES89]

2 hours ago, Ronnie said:

This is a brain twister.  I would check and see what codes you have after driving with the O2 sensor unplugged. The only other thing I know that happens when the temp hits about 160* is the ECM will allow the the torque converter to lock when conditions are right. On my car this can happen just before the engine temp gets high enough to go into closed loop. You could disconnect the electrical connector from the transmission and drive to see if that makes a difference in the bucking. I doubt it will but it's worth trying and swapping the ECM is worth trying to see what happens. Changing the crank sensor is an option to but it would be really odd that it started giving a problem at the exact time the ECM goes into closed loop. Other than that right now I'm stumped.

Codes are;

 E013 C and H

 E024 H

 E027

 E028H

 B124H

 Cleared the codes and all that came back was E013 which was expected as the 02 is still disconnected.