88 problem, has me stumped

[KDirk]

Have a problem on my 88 that I am trying to iron out, hoping somebody here can add useful advice since I am getting no where so far.

I am not getting a VSS (speed sensor) signal to the ECM. This is causing the TCC not to lockup in 4th, impacting driveability and fuel economy.

Some background:

The VSS is mounted to the transmission, and is an inductive sensor. Two wire circuit [yellow/purple], goes to the BCM first. BCM then re-transmits this data the ECM on a single wire [brown].

Here's the stupid part. The BCM is getting the sensor data (matches the speedo while driving) so the sensor and it's wiring to the BCM are good. The single wire that sends the signal from the BCM to the ECM is good on a continuity test, yet the ECM Data paramter ED12 will only show "0 MPH". Have changed the ECM and BCM both, still not working.

Any advice on where to look next is appreciated since I'm out of ideas.

KDirk

[padgett]

Did this suddenly start or did it occur with some other change ? First thought is wrong ECM or BCM PROM. What trouble codes are set. See diagnostics for code EO-24. BTW the signal gets some conditioning in the BCM.

[Guest Mc_Reatta]

So BD60 and the IPC show the proper speed, but ED12 shows 0 mph?

Do BD61 and ED11 both show the same value for the engine rpms?

In 88 the VSS sent signal to BCM that buffered signal calculated speed and distance, and sent buffered signal on to ECM

In 89 on, VSS sent signal to ECM that then buffered the signal and sent to BCM where speed and distance were calculated.

Buffered signal is 4000 cycles per mile if you can measure. Unbuffered signal from VSS is 40,000 cycles per mile.

If speedometer and odometer display properly on IPC, I wonder if you have an 89 PROM in your ECM instead of an 88 which can't properly interpret the buffered signal from the BCM, but is looking for an unbuffered signal direct from the VSS?

[KDirk]

This has been a problem since I bought the car a few weeks ago. Sets code E024 when it hits 4th gear and it realizes the TCC isn't engaged due to lack of VSS data to the ECM. Going into ECM data, it will only read 0 mph (no signal) on parameter ED12. Doing the same for BCM data does show the proper speed. RPM's show correctly in both. So, the VSS is talking to the BCM, but the conditioned signal from the BCM is not getting to the ECM for some reason.

Now, that said, when I pulled the ECM someone had written "88 Riv/Reatta" on it in paint pen, most likely salvage yard markings by the looks of it. So, I figure it has been replaced before. What I don't know is whether the MEM-CAL was swapped from the original, or if they simply swapped the whole unit from the donor car. In which case, maybe the MEM-CAL is bad, or is wrong. I swapped it into the replacement ECM and still have the same symptom.

Guess I need to find a known good MEM-CAL from an 88 parts car to test that theory. Aside from that, I am out of ideas since all the wiring checks good, and I know the sensor is sending the data to the BCM. Also found out that the BCM cannot be changed so easily. Even by swapping the two socketed PROMS from my BCM, I found there is a third soldered in PROM (maybe an OTP device, no UV window on it) that contains verification data (VIN and checksum perhaps) that causes the odometer to read ERROR. Also, option content was wrong since my CRT splash screen changed to "Riviera by Buick" and the fog lights turned on when the doors were opened. Makes me think this third PROM holds the option content, so it is more likely an EEPROM. None of that is really important, since the original BCM is apparently good, and is now back in the car.

So, until I get a MEM-CAL or a flash of brilliance, I am stuck. Unless someone else has a great suggestion for something I have overlooked.

Padgett, while I am on the subject of PROMS, do you have an 88 with the corrected BCM PROM in it? I think it was code ANCX, mine is not so I wonder if the fuel economy readout is wrong (if I recall properly, this was an issue in the original release BCM PROM, corrected in the later ANCX chip). Wondering if I can get an image and burn one to update mine, since I'm not sure these are still available as a service part.

Edit: MC, what you are saying makes sense. I am questioning whether the ECM that was in the car is right (or at least the MEM-CAL chip). I am also wondering if the 88 and 89 ECM's were the same, just different MEM-CAL's. If not, then my replacement ECM may not be the right unit either.

Looks like a job for Jim Finn, hopefully he has a good 88 ECM with a MEM-CAL in it available. The only way I can rule this out now is to be sure I have the right module/chip combo.

As an aside, the car is running rough even after a tuneup. New plugs, wires, air filter, swapped a different ICM and coilpack in, cleaned the EGR and verified operation of all 3 solenoids, also cleaned the MAF and throttle body but no change. Still rough under 1500 RPMS whether cold or hot, smooths out (mostly) above that but fuel economy is poor no matter how judicious I am on the pedal.

Exhaust has a definite odor as though it is running rich, despite what the diagnostics say. Shifts are also very slightly harsh (moreso on downshifts than up) if this means anything relative to the other problems I'm having.

No lack of power really, so I do not suspect a FPR or pump problem but will throw the gauge on it this weekend. IAC seems to read normally in diagnostics, as does the o2 sensor and cross counts. BLM is 128 on the nose, fuel int is just a touch high; 130 I think was the latest reading I got, but does move around slightly. Have brand new battery installed, voltage readings are consistently 13.5-14.3 volts at the CRT. E024 is the only code I am getting.

Going to put a Delco ignition setup on it next week when I get the mounting adapter plate (have the ICM and coils) but that will not likely change anything.

KDirk

Edited May 14, 2011 by KDirk (see edit history)

[padgett]

I have an ANCX that I bought and then used for a base for my experiments. Harry, was it you a few years ago that got the wrong BCM PROM and was reading 255 mph (maximum possible) ? Does sound like an 89 PROM in an 88 would not read anything.

The PROM code is on a sticker on the window in the PROM itself so you have to remove the BCM and ECM, then remove the cover (1/4" nutdriver AFAIR) and should see the PROM and sticker. The code for a Reatta will be four letters for both (actually both are the same PROM, just use different carriers).

I show 88 BCM PROMS as AKTH and AMTR; ECM: ANBM, AJSF, ANBL, ANCX (revised)

My problem is that lately I have had very bad luck flashing PROMs. I replaced my burner but that did not help and wonder if it may be related to aging PROMs. Have replacements but lack motivation.

BTW the smaller PROM without a window is an EEPROM that holds non-volatile settings that change such as user preferences, and the odo reading

Edited May 14, 2011 by padgett (see edit history)

[Ronnie]

Going to put a Delco ignition setup on it next week when I get the mounting adapter plate (have the ICM and coils) but that will not likely change anything.

What mounting adapter plate? If you have the right ICM and coils it should bolt right on. I have an '88 model and I installed a Delco setup and all three bolts lined up without any adapters.

[padgett]

If you go to a yard, you get everything. The Magnavox has the mounting plate built into the ICM but the Delco is a sandwich - coils, ICM, base plate. Delco also needs six screws to hold it all together. A list and picture of all the parts is on my web page.

[Ronnie]

I stand corrected. I was taking about the "mounting bracket" that bolts to the engine. I went to the salvage yard to get mine as Padgett suggested and it already had the "mounting plate" on it.

Padgett, thanks for providing us with such a wealth of information on your website. You should make references to it more often. As you know I make reference to it in several places on my website and I'm sure visitors to my website find it very useful.

[KDirk]

Padgett,

Now I'm confused. I thought ANCX was a revised BCM PROM, your last post references it as an ECM PROM (that would be inside the MEM-CAL module). Is that correct? I will cross check my PROM codes against the list you have posted to see if I have an incorrect part. In any case, if you have an image of the ANCX PROM, I could burn my own (have the hardware to do so) if there is a way I can get the file image from you. Please let me know if I can buy, borrow or beg a copy. I may also want to talk with you about the changes you made on the cooling fan setpoints, but that is something to worry about after I get the car running right.

I'd probably use a new EEPROM to burn one or even an OTP, it seems a lot of UVEPROMS that are sold now are used pulls, and their reliability is questionable. Since the EE versions are almost universally compatible with their UV predecessors of the similar part #, I see no reason to keep using UVEPROMS as they are a bit more temperamental on reprogramming.

Meanwhile, I'm going to recheck the wiring between the BCM and ECM to be positive the VSS line is making good contact on both ends. I get continuity with a meter when back-probing the connector cavities, but I suppose the pin/socket may not be making as unlikely as that is. I guess I could pull out my oscope and see if the BCM is outputting the signal, in which case I can rule it out as being bad with 100% certainty. Then, that only leaves either a bad ECM MEM-CAL, a bad replacement ECM (possible but unlikely since the symptoms are exactly identical) or something else that I just plain haven't thought of.

KDirk

[Guest Mc_Reatta]

Pretty sure EPROM in ECM is the issue. The BCM is outputting a sgnal on the brown wire, however a '89 EPROM in the ECM is not looking for an input there so it is ignored. It is looking for a x10 speed input on VSS input at 2B9 and 2B10 which probably aren't used in your 88, thus 0 mph.

You can get an idea if the signal is on the brown wire by looking at the voltage at speed. Should be about half the logic value ~ 3 to 4 volts assuming 7 volts is high. Just shouldn't be 0 or 7. (If logic high is 5 volts would be lower) O scope would be better of course.

If you really want to hang like a bat under the dash, you could jumper the VSS signal from the BCM to pins 2B9 and 10 on the ECM and then check ED12.

Wonder if other issues might be due to this EPROM?

Edited May 14, 2011 by Mc_Reatta (see edit history)

[KDirk]

MC,

I am thinking the PROM (MEM-CAL) may be wrong since the ECM has been changed at some point. I need to pull the cover of the ECM and look at the code on it and compare it to those that Padgett listed above. If it isn't on the list he posted for use in an 88, then I have my answer. Of course, there is also the chance the MEM-CAL is the right one, but is damaged.

If I jumper the VSS signal to the ECM, I suppose I would get a reading but it would be off by a factor of 10. Since the ECM expects the raw signal divided by 10, I guess 10MPH would show in ED12 as 100MPH by doing this. Might be worth trying, but if the PROM is wrong then really no reason to look any further. Will check on this today and report back.

KDirk

[harry yarnell]

Yes it was me who had the 225 mph readings, but that was when I installed a 3800 powertrain (with a 4T60 trans) out of a '87 Park Ave into a '86 Fiero. No BCM's in either.

Can't remember what I did to correct it.

[padgett]

Probably either changed the VSS or got one of the adapters. ANCX is the factory update for the 88 ECM. P/N is 16123488.

GMPD alternate catalog lists it, wonder if available:

Item Number MSRP Price

16123488 $86.05 $44.74

CALIBRATI

BTW, the PROM is just a memory device. If damaged a lot more than just the speedo would probably be affected. My guess is that it is the wrong one.

BTW the PROM id is one of the diagnostics - a four digit number

No promises but think the ANCX is a 3534 and the ANBM (original) 2544 or 2541

Edited May 14, 2011 by padgett (see edit history)

[wws944]

As an aside, this is all very interesting. It might be useful to create a table and store it somewhere (like, at Ronnies site) of which versions of which EPROMs go with which years cars.

For example, my '90 was built in 7/90. The ECM "MEM CAL Number" (from ED99) is 8064. The BCM PROM ID (from BD99) is 244.

What versions have others found in their cars? I would imagine that each year is unique. But are there multiple versions within any given year?

[padgett]

Typically for just Riviera and Reatta there are at least four for each year not counting the revisions: Think of a matrix of 2.73 vs 2.97 axle (speedo calibration) and California vs everyone else. Other car lines (Oldsmobile, Pontiac) have their own.

To get some ideaof the Proms Buick "E" you need three documents:

1) 1993 Buick "E" "Parts and Illustrations Catalog" page 3-31

2) 1988 Prom info (.pdf)

3) Buick TSB Bulletin 90-6F-8

As you can see, there were quite a few and not all information is in any one place. Couple of yeas ago I cut a CD with everything I had (proms, bins, disassemblies, codes, ALDL info, & guesses - several hundred MB) and sent to those who asked (one to Ryan). Nothing ever came of it.

8064 is a federal revised 1990 Reatta (see the TSB)

88prom.pdf

Edited May 15, 2011 by padgett (see edit history)

[wws944]

Thanks! So for Reattas, ECM would be something like:

Year Fed Cal

88 3534 ???? (maybe 2544, 8674, or 9124)

89 1094 1104

90 8064 8074

91 ???? ????

What about BCM?

Edited May 15, 2011 by wws944 (see edit history)

[padgett]

91 is in the chart in the parts book (online).