Ronnie Posted February 6, 2023 Share Posted February 6, 2023 13 hours ago, jg2003 said: As the car was let idle it started to behave better and was able to shift gears no issue. This statement makes me wonder about a problem with the PCM. It seems to say when the engine runs better the transmission shifts better. The PCM controls both. The problem seems to be so inconsistent that it's going to be hard to track down what is causing it. Link to comment Share on other sites More sharing options...
jg2003 Posted February 6, 2023 Topic Author Share Posted February 6, 2023 13 hours ago, 2seater said: Did you get into diagnostics and see what the indicated ignition timing was? The fuel pressure sounds about right but a bit more detail about the conditions under which it was obtained would be helpful. Normally the IAC, idle air control, will supply enough air to start the engine without touching the throttle, but I get the impression you needed to open the throttle a bit to get it to start and run? Did the MAF sensor look like the one on the right or left in this photo. A 1991 should use the model on the right, but either style will bolt on. It looked like the one on the right and seemed clean. Also what would be the path to access ignition timing from the diagnostics mode?. Alright so car is currently running rough. The first time it cranked started then sputtered. Again like yesterday put my foot on the gas as i turned the key and the car was able to roughly start like it was off or running rich and then slowly was able to adjust and idle without input. The car went into the weird no rpm/high idle mode fan kicked on again I also noticed a significant increase in temperature below the car the air coming up from the exhaust kind of caught me by surprise it was almost instant. The car seems to be overheating or something however it reads good temps and coolant and oil are good. Also Psi reading was with the car running it got 45 psi and 40 in start position. So symptoms so far rough idle, sluggish acceleration, and the mysterious no rpm mode coming on and off. This weekend we are gonna get around to checking out the cam sensor/magnet, putting in a new fuel filter, and inspect the spark plugs. Anything else I should take a look at?. I'll also check out the wires 2seater mentioned. Do yall think a bad ICM would cause some of this ill go ahead and check it out and take pictures to check its condition. P.S is there anyway to share recordings I think that would probably help a lot in descriptions. Link to comment Share on other sites More sharing options...
jg2003 Posted February 6, 2023 Topic Author Share Posted February 6, 2023 Okay so whenever the car exits the no rpm display mode and the reading returns it usually sits at around this Then the car calms down and idle lowers to about this Link to comment Share on other sites More sharing options...
Ronnie Posted February 6, 2023 Share Posted February 6, 2023 23 minutes ago, jg2003 said: Do yall think a bad ICM would cause some of this ill go ahead and check it out and take pictures to check its condition. P.S is there anyway to share recordings I think that would probably help a lot in descriptions. I think the ICM could cause the problems you have but lots of other things could to. Replacing the ICM with a known good one is the best test. The ICM could account for the tach reading going out as well. The next time it goes out, wiggle the connector on the ICM and see if it starts working. When the idle goes out you can go into diagnostics and look at ED11. It should display the RPM. If it does there is probably a problem with communication between the IPC and the BCM (maybe PCM on a '91?). The idle in your photos looks normal. It goes high at startup and then settles down to around 700. That is what mine does on a cold start. No direct video uploads to the forum but you can post a YouTube video. Link to comment Share on other sites More sharing options...
2seater Posted February 6, 2023 Share Posted February 6, 2023 I am kind of leaning toward the PCM like Ronnie mentioned. This erratic behavior and some of the seemingly unrelated items turning on and off sounds very much like how my car acted when I was having apparent chip connection problems in my ECM. I do not know anything about the PCM on a 91, or even if it has a replaceable Prom. 1 Link to comment Share on other sites More sharing options...
2seater Posted February 6, 2023 Share Posted February 6, 2023 Rock auto lists a Cardone reman PCM for $100 and does state that the PROM must be transplanted. As for a junkyard search, the info states it was used in the majority of GM vehicles, including pickups, from 1991-1993. At the minimum, I would locate the existing PCM, remove it, unplug and reseat the PROM and spray the connectors with contact cleaner when reconnecting the harness. You should be able to leave it hang on the floor to test for improvement. 1 Link to comment Share on other sites More sharing options...
jg2003 Posted February 6, 2023 Topic Author Share Posted February 6, 2023 (edited) 5 hours ago, Ronnie said: I think the ICM could cause the problems you have but lots of other things could to. Replacing the ICM with a known good one is the best test. The ICM could account for the tach reading going out as well. The next time it goes out, wiggle the connector on the ICM and see if it starts working. When the idle goes out you can go into diagnostics and look at ED11. It should display the RPM. If it does there is probably a problem with communication between the IPC and the BCM (maybe PCM on a '91?). The idle in your photos looks normal. It goes high at startup and then settles down to around 700. That is what mine does on a cold start. No direct video uploads to the forum but you can post a YouTube video. I went into ed11 while the rpm was out and it displayed zero. Also car used to start at first crank now it needs gas input to get it going at all. It sounds super choppy at idle then when it settles it sounds fine however i need to keep my foot on the gas for like 3 minutes for it to stay in idle once I lift off my foot. I'm kinda stumped at this point any ideas?. Edited February 6, 2023 by jg2003 Link to comment Share on other sites More sharing options...
Ronnie Posted February 6, 2023 Share Posted February 6, 2023 I think your cheapest first step would be to go to a junk yard and pull an ICM with coils. Get them off a car that looks like the engine was running when it was sent to the yard. Should be around $35-50. That would rule the ICM out and if that doesn't fix the problem you will have a spare. Some of us carry a spare ICM and coils in the trunk, along with several other parts that can be easily replaced on the side of the road. Next, I would replace the crankshaft position sensor just to rule that out. It's not too expensive and not to hard to change. It sends two signals to the ICM. Perhaps one of them isn't getting sent to the ICM correctly and that is killing the tach and causing the engine to run poorly. A wiring problem between the crank sensor and the ICM could do the same thing. Next would be replacing the PCM. I saved it for last simply because it's the most expensive but you could replace if first if you think it's more likely to be the problem. It shouldn't be too hard to change. From reading your posts I don't think fuel pressure is your problem. Link to comment Share on other sites More sharing options...
jg2003 Posted February 6, 2023 Topic Author Share Posted February 6, 2023 (edited) 26 minutes ago, Ronnie said: I think your cheapest first step would be to go to a junk yard and pull an ICM with coils. Get them off a car that looks like the engine was running when it was sent to the yard. Should be around $35-50. That would rule the ICM out and if that doesn't fix the problem you will have a spare. Some of us carry a spare ICM and coils in the trunk, along with several other parts that can be easily replaced on the side of the road. Next, I would replace the crankshaft position sensor just to rule that out. It's not too expensive and not to hard to change. It sends two signals to the ICM. Perhaps one of them isn't getting sent to the ICM correctly and that is killing the tach and causing the engine to run poorly. A wiring problem between the crank sensor and the ICM could do the same thing. Next would be replacing the PCM. I saved it for last simply because it's the most expensive but you could replace if first if you think it's more likely to be the problem. It shouldn't be too hard to change. From reading your posts I don't think fuel pressure is your problem. Upon further inspection it seems I might have bad sparkplugs. Car is most definitely showing some signs of that especially at idle. It sounded like the little v6 was cammed at one point. I'll see if sparkplugs do anything fuel filter also. I'll look into the icm as well. Also my gas pedal seems mushy/loose any recommendations on how to fix it or look into it? Edited February 6, 2023 by jg2003 Link to comment Share on other sites More sharing options...
Ronnie Posted February 6, 2023 Share Posted February 6, 2023 I've never known bad spark plugs to cause the tach to quit working... 1 Link to comment Share on other sites More sharing options...
2seater Posted February 7, 2023 Share Posted February 7, 2023 This is an excerpt from my engine build and s/c addition. If any of you read that long affair, I had on and off poor running, failure to start, perfect running and loss of data on the dashboard all mixed together, but all centered around the PROM and ECM: "Update on the control system problem which pretty much confirms my previous post about the chip being bad or unable to communicate. Acting on Ryan's suggestion after receiving some new chips, I loaded the problem child S/C 1.4 tune on a new chip. After installing, the car started and ran perfectly. Going through diagnostics while the engine warmed up, everything looked normal. When it reached closed loop, there was a change in the sound of the engine, but it all went smoothly. I then shut down and installed the suspected problem chip and even though it started immediately, I could tell something was "off". Going to diagnostics showed "no ECM data" again, so I suspect it is running in a limp mode. According to Ryan, this means the ECM cannot communicate with the chip. All this chasing the tail of the real problem, looking in the wrong place and blaming the Memcal or the Moates adapter, was at least instructional although time consuming." Maybe I can iron out some of the small details before it is time for it to sleep for the winter.👍 1 Link to comment Share on other sites More sharing options...
Padgett Posted February 7, 2023 Share Posted February 7, 2023 Just something stupid but the ALDL connector cover under the dash closed ? It completes the LAN loop. 1 Link to comment Share on other sites More sharing options...
jg2003 Posted February 7, 2023 Topic Author Share Posted February 7, 2023 (edited) 19 hours ago, Ronnie said: I've never known bad spark plugs to cause the tach to quit working... It seems they hadn't done any basic maintenance to the darn thing it's probably going to be multiple things that add into it by the looks of it. 19 hours ago, Padgett said: Just something stupid but the ALDL connector cover under the dash closed ? It completes the LAN loop. Huh I covered it and it started first crank.....mind you it didn't run very well but no gas input this time will have to test tomorrow. Also yeah car for sure isn't firing on all cylinders will check and replace them. Update nvm it didn't do anything but at least it's covered now should I check my IAC? I'm also gonna look into my fuel regulator and see if that went bad. Edited February 7, 2023 by jg2003 Link to comment Share on other sites More sharing options...
Padgett Posted February 7, 2023 Share Posted February 7, 2023 1: diagnostics allows turning off individual injectors to see what is not firing. 2: see here. Link to comment Share on other sites More sharing options...
jg2003 Posted February 8, 2023 Topic Author Share Posted February 8, 2023 13 hours ago, Padgett said: 1: diagnostics allows turning off individual injectors to see what is not firing. 2: see here. Hey padgett would I access the injectors through the ecm data or which path would I take ?if you could help give me the path for that through the menus that'd be helpful. Also is there any registry on what normal healthy sensor readings would look like I'd like to cross reference whenever I take a look through mine. Link to comment Share on other sites More sharing options...
Padgett Posted February 8, 2023 Share Posted February 8, 2023 Need to study the diagnostics here. See ECM Overides>ES10. Note the !!! 1 Link to comment Share on other sites More sharing options...
jg2003 Posted February 8, 2023 Topic Author Share Posted February 8, 2023 (edited) Welp update I guess we redid the pressure test and car gets pressure up to 40-45 psi in on position but doesn't hold it quickly drops to zero. So fuel system -w- any tips on diagnosis? Fuel regulator is dry no leak, fuel pump primes. Edited February 8, 2023 by jg2003 Link to comment Share on other sites More sharing options...
Padgett Posted February 8, 2023 Share Posted February 8, 2023 My first thought is a bad oil pressure sender (common, I usually keep a spare). ECM gives a 2 second shot with key-on, then switch in sender takes over. Can monitor signal on green prime connector. BTW the 91 uses a different oil pressure sender than other years. Link to comment Share on other sites More sharing options...
jg2003 Posted February 8, 2023 Topic Author Share Posted February 8, 2023 (edited) 6 minutes ago, Padgett said: My first thought is a bad oil pressure sender (common, I usually keep a spare). ECM gives a 2 second shot with key-on, then switch in sender takes over. Can monitor signal on green prime connector. BTW the 91 uses a different oil pressure sender than other years. Well....the mystery has been cracked quite literally the fuel tank is leaking. Which is why the damn thing won't keep pressure at all. Alright so here's the situation I either buy a brand new one for 200 and get someone to do the job. Or we go hunting for a junk part or idk if someone might have one that y'all know of. I'm leaning towards just getting a new one. Now comes the briefing how hard is the job of dropping it out? If it's a paint in the ass I'm either going to get a driveway mechanic to do it or a shop. Well I'm starting to hate the guys that sold me the damn thing but it is what it is. I'll get it running somehow. The car is in great shape just wish they'd have been honest about the fuel tank being bad. Edited February 8, 2023 by jg2003 Link to comment Share on other sites More sharing options...
jg2003 Posted February 8, 2023 Topic Author Share Posted February 8, 2023 What cars would I be able to pull parts out of fuel tank wise or is ours a one make type of thing?. Link to comment Share on other sites More sharing options...
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