Red1990VT

Tom,

Thanks, I am just getting back to this, and will definitely pull the module for testing, and then either put it back with heatsink grease or put in a new one with the grease. Good point about this. The module may work fine at idle when cool, and then partially fail for lack of proper heatsinking. I'll let you know as soon as I'm able to actually pull, test and either reinstall or replace the part.

Red1990VT

Thanks for taking such an in-depth look at the data...I noticed the O2 sensor swinging so thought it is probably working ok. It may well be the original )2 sensor, and could probably stand replacement.

The rich condition at higher RPMs seems to lend itself to the theory that I might actually be dealing with an ignition problem. Unburned air fuel from an ignition misfire would express itself as a rich condition, as you noted at above 2000 RPM. I'm looking into this...and hoping that if there is an ignition problem (see earlier reply to Tom above) that fixing that might also fix the rich condition and stumble under load.

Thanks again, you clearly took some time looking at the data and I appreciate it.

gungatim

I can't open the file in excel for some reason. converted it to pdf and it's 364 pages so not easy to read, but I don't see any codes set in those columns. the couple of things I am wondering about is vacuum under load. Wonder if you've got a clogged cat, or a compression problem. Can you do a compression leakdown test?

Red1990VT

I haven't done a leak down test and would probably have to pay to get that done. I did a compression test when I got the car, and all cylinders were around 150, with the rear passenger side cylinder around 130. So, lower than the others, but not particularly low.

For the cat, I observed the vacuum gauge while keeping the car at 3000 RPM for several seconds, and there was no drop off in vacuum. I'm not sure this is conclusive, but from what I've read, if the cat were clogged, the vacuum would slowly drop off, and in my case it held.

And no codes have been set. I did get codes when I disconnected the MAP and TPS sensors while doing some tests, but cleared those, and with test drives and considerable idling, no codes have recurred. So, looks like the ECM will see problems and set codes properly, but in operation, none are being seen.

I'm not sure what the problem was you had with Excel, I was able to import it and open it with everything in the correct places...

Thanks for your reply, as I get back to testing I'll post results.

lionelhutz

I looked again and you do have something strange with your vacuum. You have lines with low throttle and high MAP which doesn't make much sense. The worst one was at time 1199 which shows 98.2 kPA for the MAP and 0.2% for the TPS. So, it's detecting no vacuum in the intake with the throttle fully closed. Time 200.9 is another odd reading that shouldn't be possible.

Think of the MAP signal as 0 being full vacuum and approximately 100kPA is no vacuum.

I'd remove all the raw columns and any column that doesn't change or is of an unknown/unused type. Use the sensor data to examine because that is converted to readable units and values. Makes it much easier to look at.

One other thing to note, when in closed loop you can't just examine a single line and say the O2 is reading <0.45V or >0.45V so the engine is lean or rich at that point like cardo0 posted. It just doesn't work that way. When in closed loop, the O2 sensor voltage will constantly oscillate above and below 0.45V as the control loop centers around stoichiometric. The only time the O2 can be of some indicative value that way is when you are in open loop power enrichment mode where the O2 should show read rich.

WinALDL has tables which average a bunch of readings. Filter the table so it only displays when the number of data points is >10 or >25 or something like that and then look at those tables where it populates data to see if it's rich or lean.

terry82

the way I check for a plugged cat is with a temp gun check the temp going in the cat and the temp going out.

Red1990VT

Great catches! One strange thing the car does that might explain almost no vacuum with the throttle plates closed could involve the IACs. I've noticed that sometimes the car will go 35MPH with my foot off the gas on level ground. After disconnecting all vacuum connections, and test driving, it still did it. Spraying carb cleaner all around the manifold TB mounting plate, and Manifold to engine interface yielded no RPM change. So, I tried (after reconnecting all the manifold connections) plugging the IAC openings and going for a test drive. The car would not keep going if I let off the gas (throttle plates closed). Unplugging the IAC ports and test driving again - 35, even 40 MPH on level ground, foot off the gas. Not always, but often.

That tells me something is causing the ECM to command the IACs to let more air in while the car is moving and the throttle plates (and TPS is indicating) closed. My suspicion is that a misfiring ignition is letting an overly rich (unburned) exhaust stream go by the O2 sensor, which the ECM is reading, and deciding that (assuming the injector pulse width has been reduced) more air is needed - and the IACs are commanded to open up. If correct, this points to an ignition problem, something I still need to troubleshoot.

Thanks for such a thorough reading of the data. I'll go back and take another look the way you suggested.

Red1990VT

Yes, I've heard of that, and thought about buying an IR temp gun - your welcome post reminds me I need to do that.

Once I've gotten the gun and taken the readings I'll post the results. In some ways I almost wish it would be a clogged cat - that might be easier to deal with than an ignition gremlin, or some other continuing mystery problem.

Thanks!

terry82

everything is fine until you go up a hill?.I would jack up the front of the car with it running and see what happens.

Red1990VT

No, it is at its worst going up a hill, but any significant load, or abrupt opening of the throttle even on level ground will cause a severe hesitation, and if I don't back off and feather the throttle, stalling out. And WOT on level ground leads to a bunch of rumbling and stumbling with very little actual acceleration. Oddly enough, opening the throttle abruptly down hill doesn't exhibit any of the symptoms, the car picks up more speed. But level out or go up hill and abruptly hit the gas, and it stumbles and hesitates.

Also, the problem is mainly after the car is up to 25 mph or more. It idles smoothly and from a stop accelerates well, as long as I don't really hit the gas hard. Once it's up past 25 or so, and under load, the problem manifests itself.

alconk

This is very interesting and must say you have covered all the items I would have looked at as well but could it possibly be the ECM be the culprit? I mean it doesn't make sense going up hill but you never know. Keep us informed cause I'd like to know what the problem is too. Oh by the way my 82 shifts soon into OD as well and it has a aftermarket PROM. Just the nature of it unless you get a 700R4 from '88 and on.

terry82

I would pull the fuel pump and look at the hose from the pump to the metal line .they sometimes leak and act this way .

74 LS4-454

Just for fun, besides a possible ignition problem, check all wire connections in and outside of the ignition, (I had a broken coil wire under the cap, which was making the engine shut off and on at high speeds, and then eventually broke completely and the engine shut down) making sure complete contact is made. Just check and recheck every possibility. And also just for the heck of it, change that fuel filter once again.......Tom

terry82

:smas h::banghe ad:

lionelhutz

No, that's not what the PCM will do.

There is a throttle follower function on the IAC motors but it should just open the IAC enough the engine doesn't stall when you snap the throttle closed, not open the IAC so much that the car will continue to drive 40mph without any throttle. The IAC's also should not be able to pass enough air to drop the manifold to atmosphere pressure.

lionelhutz

The PCM has NOTHING to do with your car shifting into OD to early.

Get over this people. THE COMPUTER DOES NOT CONTROL THE SHIFTING OF ANY GEARS IN A 700R4. TCC lockup ONLY. Quit spreading the BS.

cardo0

Not so fast with the O2 assumption. If the ECM could not average the O2 sensor output then it would never be effective in controlling fuel mixture. Though the O2 sensor outputs a varying (sinusoidal) voltage signal the ECM has to average and trend the O2 sensor output when in closed loop. It doesnt even look at the O2 sensor output in open loop (WOT).

A quick test for this - and the O2 sensor itself - is to induce a manifold leak while taking data - this should show lean and low O2 readings (pull the power brake vac line if u can keep it running or maybe a smaller line). Next u can use a little propane to the intake to create a rich condition - again while taking data this should show a rich condition.

Hope this helps ya Red.

Red1990VT

Good Morning, another Spring day...

The fuel pump was replaced last June and consistently shows around 13PSI with a gauge tapped in between the throttle bodies and taped to the windshield so I could observe while driving (and stumbling uphill).

The ECM and PROM were both replaced, and helped tremendously. The prior ECM had gotten corroded by being right next to the battery; it is now over in the compartment with the jack. The spark control module usually mounted to the top of the ECM is there too. And the PROM is the latest factory revision, and replaced the Hypertech aftermarket PROM that was in the corroded ECM when I got the car some years back.

The IACs seem to have enough control to move the car at 35-40 MPH on level ground, because plugging the IAC air passages causes the car to decelerate quickly when the throttle plates are closed. My understanding from the FSM is that the IACs will open when the VSS indicates speed, and the TPS indicates idle, which together the computer interprets as a deceleration - and opens the IACs enough to prevent stalling but (in correct operation) not enough to act like a cruise control. I was suspecting that the ECM was reading an overly rich condition and opening the IACs to compensate, but that's purely a guess at this point. Something is however causing the IACs to open enough to move the car briskly on level ground, since plugging those air passages stops that behavior. More to come on this.

And thanks for the tip on the O2 sensor check, it is easy enough to run WINALDL and observe the O2 swings while creating a vacuum leak. I'll give that a try today and let everyone know what happens...

Thanks to all, this has been great getting everyone's help and ideas.

Red1990VT

Oh, and I almost forgot...the ECM controls a "Transmission Converter Clutch" relay which according to the FSM is like this:

"The ECM controls a solenoid mounted in the automatic transmission. When the vehicle speed is high enough, the ECM energizes the solenoid and allows the torque converter to mechanically couple the engine to the transmission. When operating conditions indicate the transmission should operate as a normal fluid coupled transmission, the solenoid is de-energized. The transmission also returns to normal automatic operation when the brake is depressed. Refer to Section 7A for ON-CAR SERVICE of the transmission converter clutch."

So, it looks like the ECM does not control transmission shifting, but does control when the transmission locks and unlocks the clutch.

My understanding is that the latest factory PROM revision moved the lock up point a bit higher in speed, because the lock up was occurring so early that the car was bogging. My experience is that the clutch will lock as early as 27MPH in some cases, which still seems too early and bogs the car a bit. But, I haven't checked the cable yet and it is possible there is a mis-adjustment at play there too...

Then again, I recall gas economy was a huge topic in the early 1980s, and I'm sure Chevy was trying to squeeze the last possible MPG out of all their cars at the time - the early lock up was probably part of that strategy, like the later 4+3 and the widely disliked CAGS.

One thing I think an aftermarket PROM is supposed to do is make the lock up occur later, but the Hypertech chip I replaced also had the TCC locking about as early as the factory PROM does.

lionelhutz

Maybe you didn't know what TCC stood for? I think every GM built with a computer and lockup converter had the computer controlling the lockup. You can unplug the lockup connector if you wanted to test without it. Computer controlled shifting didn't appear until the 4L60e and 4L80e transmissions in the early 90's and then it was all gears and the converter.

Opening the IAC's to lower the AFR makes no sense because a failure that causes a rich condition would make the engine run-away. You'd be one temperature sensor failure away from having a runaway car.



The O2 basically outputs a voltage which shows the engine is either rich (lambda<1) or lean (lambda>1) . In closed loop, the control loop in the PCM adds fuel until the O2 voltage rises and then removes fuel until the O2 voltage drops. Each data point in the log is a "snapshot" recording. So, a single O2 reading is useless to determine much of anything.

As for the testing. You don't know if the engine is already rich or lean so adding air or propane might not swing the O2 lean and rich. Besides, the O2 voltage is already swinging so closed loop appears to be working but may not actually be working because the O2 is providing improper feedback and that test won't detect that.

You need to use a wideband O2 sensor if you want to properly test the closed loop operation. Running closed loop it should tune itself so it's running right around a lambda = 1 AFR which is easy to measure with a wideband O2 sensor.