1993 Pontiac Tran sport van PCM PROM

[RO]

Need a source for the prom. Been all over the internet, ebay, etc.

Thanks

[joe_padavano]

Just curious as to why you need a PROM. The ECM or PROM is rarely the source of a problem, though it is often replaced for no good reason in a "shotgun" approach to fixing a problem. In any case, if you can't get one from the dealer (any GM dealership can look up Pontiac parts in the computer), then used is your only option. Be aware that the PROM is usually unique to the year, drivetrain, and sometimes options on the particular vehicle.

[RO]

Just curious as to why you need a PROM. The ECM or PROM is rarely the source of a problem, though it is often replaced for no good reason in a "shotgun" approach to fixing a problem. In any case, if you can't get one from the dealer (any GM dealership can look up Pontiac parts in the computer), then used is your only option. Be aware that the PROM is usually unique to the year, drivetrain, and sometimes options on the particular vehicle.

Van was dying on me and it got more frequent. Changed out the crankshaft sensor, O2 sensor, et. al and car still produced a "Code 13" on the reader and the end results after literally svereal weeks now it was believed to be the ECM. But at least two we've replaced and they go out leading to the PROM as the culprit. Indeed, extremely difficult to locate that one little piece that has the Van immobilized....it's just rediculous.

[joe_padavano]

Van was dying on me and it got more frequent. Changed out the crankshaft sensor, O2 sensor, et. al and car still produced a "Code 13" on the reader and the end results after literally svereal weeks now it was believed to be the ECM. But at least two we've replaced and they go out leading to the PROM as the culprit. Indeed, extremely difficult to locate that one little piece that has the Van immobilized....it's just rediculous.

What does "go out" mean? Have you confirmed that the replacement ECUs are actually being burned out (in which case it is NOT the PROM) or that the Code 13 recurs? I assume that the shop is simply putting the old PROM in the replacement ECU? Are you sure that they didn't damage the PROM through static discharge during one of those replacements? In any case, I am VERY skeptical that the problem is the ECU or the PROM. In my experience, "mechanics" who don't know how to troubleshoot simply replace everything in sight until they hit the problem. Even a blind squirrel finds a nut eventually. Besides, it's YOUR money, not his... Just sayin'.

[RO]

What does "go out" mean? Have you confirmed that the replacement ECUs are actually being burned out (in which case it is NOT the PROM) or that the Code 13 recurs? I assume that the shop is simply putting the old PROM in the replacement ECU? Are you sure that they didn't damage the PROM through static discharge during one of those replacements? In any case, I am VERY skeptical that the problem is the ECU or the PROM. In my experience, "mechanics" who don't know how to troubleshoot simply replace everything in sight until they hit the problem. Even a blind squirrel finds a nut eventually. Besides, it's YOUR money, not his... Just sayin'.

Yes old PROM being used. Just last night I found and ordered a replacement. I don't know if the shop could have done damage through static discharge. The shop is reputable. It just got to be the only thing left was the ECU and/or PROM as I understand it. Local place did not have the code readers for older than '95 so I had to take the Van to a place a little further away and I just cannot physically check on it every day. They tried everything I told them to try and the Van would still just be going along and quit running. Always restarted, but then it would occur again. Got to be a real nuisance. Finally I couldn't get out the driveway. Did everything I knew short of looking at the computer and prom. Three individuals all concluded the PROM was the culprit. That's all I know at this point. I believe I did see "somewhere" about some computer/prom recalls back when but I didn't own the Van back then, so total history of exactly what may have been done over the years and 138,000 miles I don't know. I can work on the old ones, but 80s and newer can't do it. The Van other than this problem is in excellent condition for the age and mileage. I am NOT discarding the old ECU or PROM during this investigation. It tool me a while to even find anyone that would at the Van. Just cannot find shops around anymore and certain things I found and learned after a dealer visit have me going elsewhere.....they're only going to service new stuff on the road. No one now days works on older vehicles.

Edited September 28, 2012 by RO (see edit history)

[joe_padavano]

So that you are properly informed, you don't need a code reader to pull down the codes on an OBD I vehicle. You can jumper the two upper RH pins in the ALDL connector under the dash and the Check Engine light will flash in sequence to display any codes.

More to my original point, MANY MANY potential causes of your problem WILL NOT SET A CODE. Sorry for shouting, but this is a pet peeve. So-called "mechanics" today are simply parts changers. They read the codes and replace what the manual says to replace. They are incapable of actually troubleshooting a problem. I have several OBD I and OBD II cars. I also purchased my own OTC Genysis Scan Tool to allow me to troubleshoot myself. Bottom line is that in ten years, only one out of ten or so problems with these cars has actually set a code. The OBD I cars are a bigger problem because the limited computer power in them limits the amount of data that the computer can collect on the drivetrain. For example, an ignition problem will not set a code (but may cause an intermittent no-start condition). A vacuum leak will not set a code. A mechanical problem inside the motor will not set a code. Today's "mechanics" appear to be incapable of dealing with this.

A quality scan tool (as opposed to a code reader) has the ability to record data on intermittent problems. You drive around with the tool connected to the ALDL connector and press a button on the tool if the intermittent problem occurs to record all available data at that point. Now, if this is a problem that doesn't set a code, the mechanic needs to understand how the vehicle's systems work and what the normal data should look like. Any anomalous data in the recorded data stream should be a tipoff on the source of the problem. It's also possible that a sensor can be out of calibration enough to cause a driveability problem but not enough to set a code, another reason why you need a mechanic who has a clue about this particular vehicle.

[Guest pfloro]

I wholeheartedly second what Joe Padavano has said regarding the GM OBD I system. IMHO, it was 'state of the art' back in the early 80s but quite primitive compared to today's computer controlled drive trains.

Having owned an OBD I car for 28 years, I chose to become very familiar with that system. Successful troubleshooting involved reading & understanding the factory service manuals (both chassis & electrical) and the willingness to 'think outside the box' while trying to solve a problem which didn't set a code. As Joe stated, most of my troubles didn't set a code.

Your trouble could be oxidation on one or more of the many (multiple wire) connectors in the system. GM's Packard Electric Division didn't gold plate the contacts in the ECM wire harnesses and it doesn't take much change in current flow to cause trouble. I was down that road a few times. I was lucky as my '84 Toronado's engine still used the Rochester Quadrajet carb. The engine would start & run (rich but able to limp home) even if I disconnected the ECM. I'm quite sure your engine is either TBI or most likely port injection. Your OBD I system is necessary to get & keep that engine running...

The entire system needs to be systematically checked.

Keep at it & good luck.

Paul

[RO]

Well, as I said, it's difficult to find a mechanic nowdays, particularly a Pontiac specific expert guru and for the 90s. It is what it is. My plate overfilled with non-1993 Van auto maintenance issues to try to dig into it. A shop seemed logical. It still seems logical. Choices are few an far between. There was no service manual with the van when I acquired it. I checked the internet, asked questions on forums, typed in key words, got feedback as to what was perceived the problem, followed through with those unsuccessfully and just had to leave in the hands of the shop. Suppose to get the Van back Monday using a new ECM with the old PROM given that there may still be some things show up on the readings. My sole interest is A to B and B to A. If they were able to get the Van to do that, then that's all I need. We'll see.

[Roger Zimmermann]

Many years ago, a dealer had a trouble to find the cause why a Trans Sport would not run as it should. They replaces also a number of parts without success. At the end, it was oxydation into the large connector at the firewall, the one with about 15 to 20 wires.

It's too long ago to remember what was the problem and if it was similar to yours. The fact that the problem came gradually let me think that there is maybe a connector problem.

When I was district service manager for US cars in Switzerland, there were a lot of ECMs and PROMs (PROM no so often) replaced in warranty for vehicles from the 90's . Were the real problems? maybe...

[joe_padavano]

Well, as I said, it's difficult to find a mechanic nowdays, particularly a Pontiac specific expert guru and for the 90s.

This isn't a Pontiac-specific problem. The Chevy Lumina APV is the same vehicle with the same drivetrain.

[RO]

Many years ago, a dealer had a trouble to find the cause why a Trans Sport would not run as it should. They replaces also a number of parts without success. At the end, it was oxydation into the large connector at the firewall, the one with about 15 to 20 wires.

It's too long ago to remember what was the problem and if it was similar to yours. The fact that the problem came gradually let me think that there is maybe a connector problem.

When I was district service manager for US cars in Switzerland, there were a lot of ECMs and PROMs (PROM no so often) replaced in warranty for vehicles from the 90's . Were the real problems? maybe...

This shop has very tediously gone through all the wires and contacts in the harness and through the firewall which has taken considerable time. They found one or two slightly corroded but didn't seem to affect overall condition after they were cleaned. They said there were 16-20+ wires, so I imagine that is it. I did find a PROM. Plan to get the Van back next week, drive it and see. and only if it gives me problems, see what a replacement PROM will do.

[NTX5467]

In my years of dealing with proms and such, at the dealership level, I never knew of a PROM to cause the issues you are having . . . with all due respect. In the GM ECMs back then, most were universal in nature AND part number. It was the basic calibration module (the longer plug-in on the circuit board of the ECM) that was the basic processor of the information from the various sensors and such. It was the PROM which customized those signals for the particular vehicle. Tire size, axle ratio, engine specs, etc. all played a part in getting things to work right. Replacement ECUs never came with PROMs installed, but did have the larger module. Without a PROM installed, engine would only crank and that's all.

Also, be aware that back then, a GM code 13 was different from a Chrysler or Ford code 13 . . . PLUS that until we got OBDII and its standardized (for OEM) codes, the codes would vary from model year to model year.

As noted, there were NO Pontiac-specific electronics back then, just "GM-specific". What your Pontiac vehicle has in it could also have been installed in a similar Chevy vehicle, or other GM vehicle for that matter.

I am surprised, though, that with all of the parts y'all have chunked at this issue that one hasn't stuck and fixed it!

The other thing to consider is that, although it's got computer controls and such on it, they were very "antique" computer controls compared to what the bulk of the current group of mechanics might have seen in their training OR knew about when they were growing up "with cars". Might as well have taken them something with a points-style ignition system in it!

One time, a Chevy C20 pickup was sent to us by a private shop. Seems it would run and the suddenly shut down . . . and nobody could find the issue. One of our techs ended up checking each individual plug-in connector in the distributor's harness. Finally found one which didn't have good continuity between the terminal and the wire it was attached to. He repaired that ONE wire connector, replaced it into the insulator, and reinstalled the whole thing to the distributor. Luckily, when I drove it on a 100 mile check-out run, it didn't fail.

A significant thing you have to remember about "codes" stored in the ECMs memory is that they, just like operational conditions on an earlier model vehicle, you have to know how the codes inter-relate AND what can cause them in the first place. Fuel and ignition can still have issues which can seem to be "the same", but aren't. One particular operational problem can also set a string of different codes for ONE problem, so you have to sift through the list and consider why each one set . . . "Perry Mason"-style.

A BIG advance in scanners happened when they came to have the memory capability to look at "snapshots" of what the various sensor readings were when the particular code was set. Yet, if all you have is "a reader", then all you get is the basic information and the capability of turning off the "Check Engine" light. Very different products with very different capabilities.

When we got the various electronic modules and such in GM, it was mandatory that the tech be grounded to the vehicle before they worked on the modules and such. This resulted in an elastic band (with a metallic conductor in it) which was they alligator-clipped to the vehicle's chassis (it had a coiled wire on it). Reason was the mentioned "static discharge" issue. This was a mandatory situation . . . in the earlier years. As things progressed, many techs "forgot" about the wristband and there was not a big spike in static electricity "zaps" causing warranty claims for ECMs and such. I'm not sure if the static electricity issue was really not that prevalent, or if there were some materials in the earlier vehicles (seat coverings, carpets, etc.) which were more prone to static electricity generation.

The PROM and the other "chip" have very fine prong terminals. As along as you pull evenly and gently, even with the supplied tool for such, AND upward, there are usually enough guide tabs on the PROM and its recepticle to keep the pins all straight and where they need to be. That's been my experience. But I've also seen some that got bent, somehow, so pin alignment of the PROM items and the similar female terminals is important.

As a general rule, we had more issues with ignition modules and Mass Air Flow sensors back then than we did with PROMS. The Buick V-6 MAFs were "famous" for this, for about three model years in the later 1990s. Cars would quit as they were crusing down the highway. Might restart, might not. Yet when they'd get back to the dealer's shop, they'd run normally . . . so "the tap test" was devised to test the MAFs . . . if you took a screwdriver handle and "tapped" on the MAF as the engine was running, it it stopped, you replaced the MAF . . . if it kept running, you looked at the ignition module (in one model year, the "Magnavox" coils were a big reliability issue) or for other issues.

One of the things which GM cautioned about was dealers installing "aftermarket" MAFs and computers on customers' vehicles. As the claimed, ONLY the GM-supplied items would meet complete GM specs and such. The TSB went on to mention that (at that time, I suspect), the "reman" operations of entities other than GM-contracted/supervised entities might not meet GM's standards OR specs for solder joint resistances and such. Plus, they would NOT accept a non-GM core for these parts, either! That meant that their contractors got ONLY GM-production cores back to go through, which also would highlight any quality control problems which might be occuring, down the road. And, I can say that there were virtually NO warranty issues with the GM reman ECMs we sold. Made some of our repair shop customers a little frustrated when we wouldn't accept their "black box" core after we'd just sold them a GM-reman ECM to replace it.

If your Pontiac has a chip key ignition key, it could be a chaffed wire from the ignition key cylinder to the computer box that runs that anti-theft VATS system. Or a key with a worn "contact" area.

IF the PROM you got is NOT an exact match for your particular vehicle (engine size and such, axle ratio and tire size combination), it might run reliably but could also have some other operational issues . . . as incorrect idle speed.

Best of luck,

NTX5467

Edited September 29, 2012 by NTX5467 (see edit history)

[RO]

Thanks very much for the valuable input and the time it took to cover all the details. Good to have a forum like this. I have printed it out for reference and will use it to provide some additional insight into the issue for the shop. The PROM I acquired is designated for the larger Van engine, original drivetrain but hopefully I will not need it.

[joe_padavano]

The PROM I acquired is designated for the larger Van engine, original drivetrain but hopefully I will not need it.

I'm not sure exactly what you mean here, but if the PROM is not for the EXACT engine and drivetrain in the EXACT vehicle, it may not work properly. The PROM incorporates the fuel map, ignition advance map, and many other data items like idle speed and torque converter lockup points that are only valid for the exact original configuration.

[NTX5467]

In the "outside world", you might get something that "will work" and physically fit the particular ECM, but as it's the PROM which customizes the signals for the particular vehicle/engine combination (of which there is NO "larger van" version of your vehicle, although there might have been a larger engine option, as a 3.8L Buick rather than a 3.1L Chevy V-6, for example) -- period. In the world of GM Parts, if the PROM's ID code didn't match exactly or had been superceded to address particular issues (a different PROM ID code, as a result, but traceable back to the original PROM code and vehicle/engine combination), in the words of ParTech, "We're not in the business of modifying vehicles. If Engineering says it doesn't fit (via GM part number), it doesn't fit (period!)"

There can be some cases where a different factory PROM can work. There was a deal in HOT ROD magazine where they'd done some mods to a Camaro TPI V-8 and needed a slightly higher base idle speed. They had a 305 TPI, so they got a same-year 350 TPI PROM to get the extra 50rpm of idle speed they needed. But that was also a situation where each car's drivetrain specs were the same, just with a slightly different engine size . . . an engine size difference where even a carburetor could have been the same and worked well. Still, NOT advisable to put a PROM where it's not supposed to be.

x2 on what Joe said!

NTX5467

[RO]

I Just meant I acquired a PROM with the same AC Delco part number for the 3.8L V6 Auto tranny which my Van has. I believe there was a smaller V6 in '93, perhaps 3.1 as mentioned above.

[sfair]

Error 13 - heated O2 sensor open.

Does the engine go into closed loop?

Were the correct voltage checks done at both the O2 sensor and the PCM?

[RO]

When they got the Code 13, they replaced the O2 sensor but the "check engine soon" light still remained on. I'm not familiar enough with it to know what "closed loop" means. The computer was replaced and the light went out at the shop. But I believe it was intermittent which caused them to focus on the PROM. But the PROM was NOT replaced. The Van was driven home Tuesday and all seems well for now although that "check engine soon" light came on again after about 10 miles. The Van was driven about 8 miles after that. No indication the Van was going to die on me. And I did in fact drive this Van from sometime around 2002-2004 until this shop visit with that light on, including nearly 700 miles at one time and then a number of shorter trips through the years. There is some "thinking now" that perhaps the reason it was randomly diying was the fact that there were two bolts cracked somewhere on the intake manifold that once in awhile caused the Van exhaust to smell like steam but once warmed up it was ok....I saw the little O-rings and they were squeezed out of place somewhat. NO coolant in the oil so there's no head gasket situation here. Not sure the nitty gritty details, but the Van was driven some time without knowing there was a problem here. I believe the shop thinks that in some way was cauising the Van to die.....perhaps sucking too much air, I just don't know. I will test drive it in longer and longer drives and see what happens....keeping a cell phone handy.

[sfair]

This particular code is pretty specific in cause and other conditions having an influence on it are remote.

It is set by an oxygen sensor that does not vary its output.

The cause of that could be a faulty O2 heater or the wiring associated, or a faulty O2 sensor or the wiring associated.

The wiring may be the tripping point if the PCM and O2 sensor were replaced with no change.

There are specific tests for the O2 sensor with a scanner to check the heater and O2 voltage. If these tests are not performed, you could be doomed to tail chasing.

Now, if the engine goes into closed loop and stays there but still sets the error code, that could be a different problem.

This code will not set instantly as there are several running conditions that must be met for a specific amount of time before the fault is set.

I am not suspecting the PROM at this time.

This is the 3.8, correct?

[RO]

Yes, this is the 3.8L. There was so much back and forth on this over a month and I do not know exactly which connections were checked but do know a good amount of time was expended in the harnesses/wiring/connectors. The shop was frustrated they couldn't get the light off, but eventually did but then after less than 10 miles came bac k on.

[sfair]

but then after less than 10 miles came bac k on.

Yes, that probably was because of the requirement of the conditions for a certain amount of time to set the code.

One thing to watch for is, not that you have an open connection, but that the connections are not high resistance. The O2 sensor operates with small voltage changes and its internal impedance is very high, so a poor connection could throw it off.

The scanner should be able to spot that if you know what to look for.

[RO]

I'll try to monitor the O2 sensor and connections. Got the Van back last week and have driven it several times and all appears ok except one time today from start and slow speed exit from a parking lot, it dies after about 100'. Restarted and got me home ok. I attribute this to too slow idle speed as it is definitely slower than previously, maybe <500 RPM judging from the sound. Is there a way to adjust idle speed up on this model?

[sfair]

No idle adjustment.

Google GM idle relearn to see if you can find one that applies to your vehicle.

[RO]

OK, thanks. I'll do that.