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1988 reatta idle & CRT problem


Reatta 89

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I bought a 88 reatta a I have two problems with it. The first is when I am driving the car and when I am slowing down pushing the brakes the seems to run up to 1100 to 1500 rpm once stopped it keeps on for about two sec. then goes back two normal. The second is CRT is acting crazy. Other than that it is a very nice car it's not causing a problem I can't deal with it is just annoying. Any suggestions would be helpful.

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I think the prom is bad in the ECM as I swapped CRTs, CRT Controllers, ECM but not the prom. Not sure about the RPMs revving. Never experienced that problem.

After further thought it could be the MAF sensor. Gibson's has a bunch, or I can get one to 2seater when we meet up.

Edited by DAVES89
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Watch the IAC (ED22) in diagnostics while driving. The IAC increases the counts in response to more foot throttle so it can sort of catch the engine when your foot is lifted, easing the rpm down rather than having it slam shut. See if the IAC is hanging up and not letting the engine slow or if the IAC counts are decreasing but rpm stays up, it is something else. 

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8 hours ago, 2seater said:

Watch the IAC (ED22) in diagnostics while driving. The IAC increases the counts in response to more foot throttle so it can sort of catch the engine when your foot is lifted, easing the rpm down rather than having it slam shut. See if the IAC is hanging up and not letting the engine slow or if the IAC counts are decreasing but rpm stays up, it is something else. 

Never thought of the IAC. That could be the culprit.

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I was on a 100 mile round trip today so I watched the IAC to see how mine behaves. Nothing about my car is stock, so don't take the numbers as gospel but I think the general trend is accurate. Steady cruise at 60-65mph on relatively flat ground, rpm is ~1800 and the IAC counts are 90-100, let off the throttle and just coast at the same speed and the TCC unlocks, the rpms stay pretty much the same and the IAC counts drop to around 70. They stay right in the 70 range for 1/2 mile or so but as soon as brakes are applied to slow down, the IAC counts drop off fairly quickly to the ~40 count number at idle. It seems there needs to be a brake signal for the IAC opening to drop off toward idle. 

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  • Ronnie changed the title to 1988 reatta idle & CRT problem
  • 2 weeks later...

Holiday weekend so my son, the new owner of the above Reatta came by the cottage. I asked what ECM PROM was being displayed and the diagnostics indicated it is 2544, which is the middle PROM for an 88, so that should be okay except for the following: Stepping through the various ECM data items, the data displayed is either wrong, misplaced or not related to the category. Some kind of weird display problem. We had a somewhat similar thing happen to the old black Reatta but that resolved with cleaning and R&R the connections. I don't know what is going on, but as far as I know, the ECM data is fed to and displayed via the BCM? The car runs fine so it seems to be display problem, but if that's not correct, hard to know where to repair? Sent him home with another 88 BCM. Is there a list anywhere for the correct BCM number for year and model? We have two BCM's #122716920 ANDM Prom and 1227333 with AMTR Prom. 

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There is. It's in the "How to" guides. Look at "Electrical Systems" and then "Computers and Sensors".

The latest version is ANCX others that would work are ANBM or AJSF.

I just checked my inventory. I do not have one. There are a number of Rivs and Reattas at Gibson's. Maybe there is one there.

Edited by DAVES89
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2 hours ago, DAVES89 said:

There is. It's in the "How to" guides. Look at "Electrical Systems" and then "Computers and Sensors".

The latest version is ANCX others that would work are ANBM or AJSF.

I just checked my inventory. I do not have one. There are a number of Rivs and Reattas at Gibson's. Maybe there is one there.

Thanks. I looked at the list of ECM Proms and that is how I determined the ANBM is supposedly in the ECM. It is the BCM and its Prom I am wondering about? I don't think the BCM has ever been decoded.

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Swapped in the 88 BCM we had in stock with no apparent change. It was a match to what is already in the car. This was from an 88 that was stripped in the 'yard a couple of years ago. Searched the spare ECM's in the parts drawer and one is a remanufactured one that was apparently pulled from the same junkyard 88 but was mislabeled as a BCM. In any case, it contains the same ANBM Prom. With all the swapping of silver boxes by both Daves89 and us, Daves theory of a bad Prom has fingers crossed this will fix it. It may be a few days before the ECM meets the car. No luck so far finding the preferred ANCX .bin file for the Prom.

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13 minutes ago, 2seater said:

No luck so far finding the preferred ANCX .bin file for the Prom.

Padgett is the .bin file man. He's not been around the forums for a while. That's not like him. I hope he's doing well.

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9 hours ago, Ronnie said:

Padgett is the .bin file man. He's not been around the forums for a while. That's not like him. I hope he's doing well.

PM'd him a week ago. I hope he is okay as well.

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I don't want to take over this thread but I have contacted Ryan @ GM Tuners and he sent me the ANCX file. This has of course caused more questions than answers. I just did a comparison of the ANBM and ANCX calibrations, at least the part we can tune, and I cannot find any difference at all. I noted I had to use a different "decoder", called an XDF file in TunerPro, to read 1988 files. This is another one of those differences between 88 and the later years. When I first looked at the files, I did so with the decoder for the 89-91, and while some of the data showed up as expected, the values were wildly incorrect. For example, closed loop enabled at -4C*. It is the type of oddity we are seeing in the onboard diagnostic display. I don't know what to think at this point. Differences in Memcals outside the tunable part or something in the system that is garbled or dyslexic? We still have a different ECM with another stock ANBM Prom to try. All the chips, Proms and silver boxes are correct for the 1988 model. 

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Take a look at anything that might have something to do with displaying fuel mileage. If I remember correctly, one of the prom updates for '88 models was to correct an inaccuracy in the calculation of fuel mileage displayed.

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2 hours ago, Ronnie said:

Take a look at anything that might have something to do with displaying fuel mileage. If I remember correctly, one of the prom updates for '88 models was to correct an inaccuracy in the calculation of fuel mileage displayed.

I think I am a prime example of knowing enough to get in trouble but not enough about why or how. Maybe Ryan will bail me out? I don't find anything in the dozens of items in the Prom that deals directly with mileage. There is a place to change the flow rate of the injectors, which allows for different flow rates to be accommodated. It that is tweaked, it might change the fueling calculation for display, but in this case, the numbers are identical. There are two tools in the TunerPro software. The "compare" tool allows the user to select a another calibration to compare too and it will show any difference between what you are working on with the reference item. It is a little graphic of a balance scale which can be clicked on and off. That is what I did for each of the dozens of items. There is another tool which I don't normally use because I haven't found the need or apparently understand it. It is called a difference tool and it will compare two calibrations at the byte location level. Despite the apparent sameness of the Proms, the difference tool says there are over 13.5k bytes difference?? It may be as simple as the counting starting one byte different or something like that. I just do not know at this point.

 

Does your '88 display data properly? If so, what Prom i.d. is displayed?

Edited by 2seater
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I received a reply from Ryan. Apparently, there are in fact over 13.5k single byte differences between the two Proms. The difference tool does not tell you what the differences mean, only that they are there as well as the location address. We, the user, only have access to a small amount of information that we can change. He used the analogy of your computer operating system vs the control panel where things can be added, subtracted or modified. So, in the end, many things may be tweaked outside of our sight, perhaps including the mileage calculation. Rather than burning a new Prom immediately, we will install a replacement of the present Prom first. 

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Installed a new ECM with Prom from another '88. The car runs flawlessly but the oddball display of incorrect data on the CRT continues. Very strange. The only thing left to try is to burn a Prom with the latest ANCX programming. The CRT locked up on the way to the cottage, apparently heat related. The vents were putting out considerable heat, much more than ambient. The A/C doesn't work yet but this was much above normal. Pulling the BCM we found the clip for the rod at the blend door was broken and the rod was loose. This may have happened when previously changing the BCM, Applied a temporary fix until a new clip can be obtained which greatly reduced the air output temperature. So far, the CRT seems happy with that. I will let the O.P. relate what caused the high rpm when coming to a stop😖

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So responding to the idle problem it was caused by me my fat foot when I went to push the brakes I also just touched the gas pedal once realized the idle problem stopped. Car overall is Great a/c now works electronics seem happy just have the weird display problem.

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What did you do to make the A/C work? The previous owner to me said it was a slow leak. As I used the car only in the winter I never dealt with it.

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By the way, I did burn the ANCX Prom but we haven't gotten together to try it yet.🤞

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