You know they do make a tool that plugs into the cig lighter socket and has a connector for a 9 volt battery ?..I have one ,it just keeps ECM power so you dont lose memory.Might want to look into it..dont know if they still sell them .I got mine back in mid-to-late 90's for that purpose.

Theres the hundredth post for this thread...

 

'91TealRS, I was wondering, how hard, or how far, and how quickly, are you hitting the go-pedal? This past weekend I was able to take out a '92 3.1L auto and do some testing. I also realize that you have a 5-spd.

From the data logs it was obvious that the O2 went way lean. The engine stayed in open loop, so no help there. OTOH, like usual, the throttle repsonse is not what I consider good. It does lag. And the O2 drops to the floor.

RBob.

 

Just a thought: how many of you have actually replaced the ECM? My 92 3.1 manual was having very similar problems. I replaced the ECM and now it runs like a dream!

 

Well, RBob, I can shift like my foot is on an egg, or I can mash it, and it still hesitates. When it's cold (open loop), you can actually feel the car slow down if you barely crack the throttle. Warmed up in closed loop, it is much better, but if you don't want to creep away from every stop sign, you have a problem. As stated before, the curious thing is that the very first push on the go-pedal after starting the engine is very smooth, but every subsequent shift is rough. If you snap the throttle open a little while idling, the idle will drop about 50 RPM before increasing. By then the throttle is closed again, and the increase is minimal. It will actually chirp the tires if you try to accelerate "normally", that is, without babying it.

The automatic uses a different PROM, as you are aware. It will idle a stick shift car at 700, but the hesitation is better. The shift light comes on when the torque converter is supposed to lockup (even in open loop), and if you start it by pushing, numerous codes are set. The shop I took it to "fixed" the problem by using this PROM, then offered to disconnect the shift light when I complained........

In open loop, the ECM doesn't use any data from the O2 sensor, so how can you tell it went way lean in open loop?
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I have heard that rebuilt ECMs are junk, and not really "rebuilt", they are just pull offs from junk cars, and checked for loose wires, and broken boards...... Did you get a new one? I have thought of that, but been dissuaded by the above info. Did the new one come with a PROM?

 

I replaced mine with a 262 ECM was a 730 dont know if that makes a difference.Mine is sluggish in open loop,and clears in closed..not completely but enough to not worry about it.

 

It is interesting about the first time being OK, then bad after that. The testing I did last weekend was an attempt to replicate that issue. I was figuring on a code problem. My results are inconclusive in that regard.

This particular vehicle has a 3-wire heated O2 sensor. So it is active shortly after start up. The ECM doesn't use it (not until closed loop), but the value is still reported via the ALDL link. Here is a graph that shows the O2 dropping. This is the first push of the go pedal after a restart. Engine is at 99 C (ca 210 F).

The second push of the go-pedal was basically the same (still open loop). Later I'll get a graph once in closed loop. Entirely different. The INT responds by adding fuel. The O2 briefly drops then recovers.

I did a quick check of the AE parameters between a stick & auto (BAWX, AZTY). Some differences, but nothing that stood out.

RBob.

 

Here is a closed loop graph. There is a lot to see in this one. But the most important item is that the O2 value recovers. The oscillating O2 value is normal, it is cross counting.

What you don't see is that at 0:1:32 the INT has risen to 145 counts. This is in response to the lean AFR from lack of AE. Notice the RPM curve, and the O2 value. In the area of 0:11:31 the O2 is lean, there is also a belly in the RPM curve.

Once the INT catches up the RPM rises at a faster rate, more power. And the O2 goes up also. At 0:11:33 the INT has actually overshot and needs to recover. As the RPM continue to rise can actually see the relation between the increase in RPM vs. the O2 value.

RBob.

 

Thank you RBob, for all the effort you have put into this, it is appreciated!!

The one thing I noticed from your graphs was the constant TPS value, and continuous increase in RPM and MPH. As you are aware, when shifting a manual transmission, the TPS and RPM are up and down constantly. I don't know what would make the first push on the go-pedal different from the later ones. It seems now that when it is in closed loop, even a restart produces the hesitation on the first push. When it is cold, and first started, I can put it in 1st, and idle down the street, then push on the pedal (hard or soft) and there is no hesitation (I don't slam open the throttle, just a "normal" rate of acceleration). Then when I shift to 2nd, the lag is very noticeable. It does seem to get better when it goes to closed loop, in fact, if I start out in 2nd gear, the lag is not really noticeable.

The exception there is when I was merging onto a freeway onramp which has on-ramp traffic, and rolled through the stop in 2nd, and punched it. It just sat there!! I thought it had died, tried to start it, but it was still running. Went to 1st gear, and got out of it, but not without almost getting rear ended!! So I guess there is a lag, I just don't replicate it very often. This car has me gun-shy now!!

Anyway, I was wondering if you could run those tests with the car in first gear. I don't want to ask you to go to neutral, then to 2nd, that is not good for the transmission, but just rev up to say, 2500 in first, then back off to idle TPS value, then hit the gas again, see what the readings are then. That would be closer to what is happening in the manual transmisson cars.

As far as the PROMs being about the same values, the shop I was talking about put in the AZTY PROM, and swore up and down there was no hesitation. I felt some, but it did seem better. He said he test drove it using a scanner, and everything checked out ok. It was when I disconnected the battery to do the timing chain that the hesitation was back, and I started my own investigation, including getting the correct BAWX PROM.

So the O2 at the low level in open loop means lean? The computer is using default values during this time, that explains the low steady reading. I assume the higher levels mean rich, so it is compensating for the leanness. I notice that the O2 reading stayed high in open loop until 00:14, where it plunged, could that be in response to the first rise in TPS value? That could answer the question about the first push, as it doesn't recover until 00:19, when, I assume, the first movement in O2 value triggered the ECM to go to closed loop, and adjust the mixture. Also at that time the TPS value was dropping, you were backing off the throttle, and the O2 stayed high.

The oscillating O2 value tells the ECM that it is working, correct? If it was constant, a code would set.

I changed the cap and rotor, and installed a fresh set of ignition wires, taking care to keep them apart. We'll see if that helps.....

Thanks again for all the help!!

 

I did end up with a refurbished unit. I suspected the original was bad (along with everything else mentioned in this thread) so I took the car to my local Chevy dealer and had it diagnosed. $120 later they confirmed my suspicion. I replaced the unit and it was like night and day!
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Oops. No, the new unit did not come with a new prom. I used my old one which is super easy to swap! Just like changing a memory stick out of a computer.

 

So there is absolutely no hesitation whatsoever now that you have replaced the ECM? Even in open loop?

The $120 was for the diagnosis only, right? Where did you get the rebuilt unit?

Do you have the updated PROM (BAWX), or the original 1992 PROM (ARPL)?

 

I have been reading some of the threads in DIY PROM, most from early 2001!! You posted in some of them, too. In one of the threads. maybe a later one, there is mention made of "deceleration enleanment", this sounds like what is going on here.

Do you have any more info on this condition?

There seems to have a lot of new software/equipment available since TRAXION's long posts on VE tables without PE.

 

I am very sorry to have been away so long and leave your questions unanswered.

No, there is no hesitation at all now. I'm afraid I don't know what you mean by "open loop," but I have not noticed any symptoms since I replaced the ECM. (BTW, I'd love to know what "open loop" is since I've seen it several times!)

Yes, the $120 for diagnosis only. I still have mixed feelings about spending it since that was probably the first part I would have replaced next, anyway. Oh, well. I guess that if the diagnosis had been wrong I could have gone back and said "try again!" I was able to get the rebuilt ECM directly from the local AC Delco distributor. (One of the guys I work with used to work there and still gets a smashing deal!)

I remember seeing BAWX on the ECM, so I assume it was the updated PROM.

The only problem I have with the car now is it occasionally gets VERY hot in stop-and-go traffic, but it did this just before I replaced the ECM, too, so I'm pretty sure it's unrelated.

If you do decide to replace the ECM let me know, I'd love to know if it solved your problem!

 

"deceleration enleanment" (DE) is the opposite of acceleration enrichment (AE). When you lift off the go pedal the ECM cuts back on the fuel delivery. This is DE and only lasts a short period of time.

The code that is running in the '90-'92 3.1l ECMs has interaction between these two functions. Going from active AE to DE changes how things are calibrated. This is an area I was looking into with the tests I ran. Still don't have an answer.

Open loop vs. Closed loop. When in open loop the ECM is running the fueling steady state. No active corrections to the AFR. What you have is what you get.

Once in closed loop the signal from the O2 sensor is being used to adjust the fueling. There are short term and long term values stored to keep the AFR at 14.7:1 and oscillating. This keeps the cat-con happy.

RBob.

 

As RBob stated in his post, open loop is when the ECM is running the fuel steady state. This happens when you first start up and everything (especially the O2 sensor) is cold. I was wondering if your new ECM hesitated in open loop, as opposed to closed loop, when everything is functioning, and the ECM is adjusting per O2 signal. Mine is a lot better in closed loop, but still stalls out if I need the power off the line.

The engine cooling fan is set to come on at around 230d, so extended idling time will bring the temp up.

I will check on rebuilt ECMs, and let you know if I replace it. Thanks for your input!!

 

I get a "lean misfire" smell when I decel on the freeway, and sometimes while idling. When I first start up, and it is in open loop, I get a nice "rich" smell from the exhaust (you know what I mean), but once in closed loop, the stinky lean smell is back.

So going from AE to DE starts a BL? If I do that more and more, will the PROM learn a better mixture, and eliminate the smell and hesitation?

I took your advice and ordered the Accel 15 lbs/hr injectors, along with a Holley adjustable FPR. This one has the spring and diaphragm included, and a more accessable **** for adjusting when the manifold is back on. The injectors just arrived yesterday, I will install both this weekend. Seems that raising the fuel pressure has the same effect as installing higher flow rate injectors. I plan to start off from a stock setting (47psi @ 0 vacuum), to see if the injectors by themselves make a difference.

I have read in these posts that it takes 40+ key starts for the ECM to really learn the tables, is this true? So any adjustment I make will take time to really see if it made a difference?

 

This might have nothing to do with your current problems,but I have noticed something odd ever since I purchased my camaro.I bought my camaro from east Sacramento and anything that has copper in it ,I have replaced it or in the process of replacing.I noticed you live in Castro Valley,near the ocean...I know they shut down Alcatraz down due to the salt water eating the metal away.Does this have the same affect on electrical components in our cars?If so maybe thats why you might be having more problems then others?.maybe this would be a question for a chemist?Something to consider?