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Old 09-18-2021, 08:33 PM   #1
kevinc
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Problems running at operating temperature

1988 C1500, 350 with auto trans. I owned this truck for several years and it never failed. I don't know where to now go with it. One morning last month, I drove it to work and 4 miles from home I was at a red light. Light turned green and the moment I touched the gas pedal to go, it died. No matter how much I tried to start it, it would not start. I had to get a tow home. Next day I started it and it ran perfect. I just let it run inn the driveway. Ran perfect for about 10 minutes, then the idle speed kicked up quite a bit. I don't have a tachometer, so I don't know how much. It ran like that for 5 minutes before I got in and touched the gas pedal. Instantly died again and would not restart.

What I have done so far...
It has good spark after it dies.
The spray cone from the injectors appear good.
I replaced the ignition module and ignition coil.

Still having the same problem. Runs perfect cold, but once it gets warm, it won't run at all.

I tried finding diagnostic info online, but can't find anything that matches my situation.

Any ideas?
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Old 09-18-2021, 09:15 PM   #2
Nick_R_23
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Re: Problems running at operating temperature

Any codes?

If you have good spark, the usual suspects are:

Bad fuel pump/bad pressure regulator/clogged filter
Bad Throttle Position Sensor
Bad Coolant Temp Sensor
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Old 09-18-2021, 10:22 PM   #3
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Re: Problems running at operating temperature

Thank you. I don't have access to a scanner. I would take the truck to O Reilly to use their scanner, but it won't make it that far. How do I test fuel pressure?
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Old 09-18-2021, 11:36 PM   #4
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Re: Problems running at operating temperature

They sell an in-line tool that replaces the fuel filter and gives you a test port, they should also be able to rent a compatible fuel pressure tester to you.
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Old 09-19-2021, 07:57 AM   #5
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Re: Problems running at operating temperature

You don't need a scanner to read the codes.
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Old 09-19-2021, 01:51 PM   #6
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Re: Problems running at operating temperature

1988 GM truck will have an ALDL (assembly line diagnostic link) jack. People call this OBD I, it's not. OBD I is mid 1990's California emissions only. Everything else is whatever proprietary diagnostics the manufacturer used.

You don't need a scan tool to read the diagnostic info from an 88.
Name:  ALDL Jack.gif
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Turn the ignition on and DO NOT START THE ENGINE.
Short the ground to the diag terminal of the ALDL jack. Terminals A & B. This will start the diagnostic mode.
  • The MIL will flash code 12 three times. Code 12 is one flash, a short pause, then two flashes.
  • The MIL will then flash the two digit codes stored in the same manner as code 12.
  • All stored codes are displayed 3 times each then a code 12 will repeat.

You can build a serial to ALDL interface and use an old PC or laptop with an actual Rockwell RS232 serial port or buy a USB to ALDL cable to talk to an ALDL equipped vehicle with WinALDL, TTS Datamaster, or Tunerpro RT.

Moates GMECM will run on MS DOS 6.22 or Windows 95/98. It doesn't play well with NTVDM so 32bit versions of Windows 2000, ME, XP, Vista, and Windows 7 will not have a lot of success running this. NTVDM ended with 32 bit Win 7 so there's no chance with 8, 10, or 11.

There's not a lot of data coming from these early ECMs. If you had a Tech1 or Tech 1a or a Bosch Mastertech 3100 you could get some bi-directional control of a handful of things. The Tech1/1a is 30+ years old and likely any you'll find will be in need of a fair amount of repair if it's even possible to resurrect them. The Mastertech is over 20 years old. They won't give you enough to make it worth the scavenger hunt to find the cartridges, cables, and working handheld tool.
I sold my Tech1 with my 1990 Corvette. I recently repaired it for the buddy that bought it from me. Capacitors, a couple other discretes, and corrosion from being stored without a plastic bag. Luckily no proprietary chip damage. The PVC diag cable jackets are cracking and they're made of unobtainium now. I don't miss it.

You're better off with a decent quality digital multimeter, analog multimeter, the GM service manuals and, maybe a 4channel scope.
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1969 Dodge Polara 500 B383, A833 SOLD
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1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
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RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; 09-19-2021 at 01:56 PM.
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Old 09-19-2021, 02:15 PM   #7
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Re: Problems running at operating temperature

Yes, it is OBDI. Reads the same up to '95.
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Old 09-19-2021, 03:18 PM   #8
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Re: Problems running at operating temperature

Quote:
Originally Posted by Just call me Sean View Post
Yes, it is OBDI. Reads the same up to '95.
ALDL (Assembly Line Diagnostic Link) and OBD I are not the same thing.

ALDL was the GM proprietary 160baud and 8291baud datalink on the computer equipped 1982-1995 GM vehicles. In North America GM used a 12 terminal Metripak 280 jack. GM Holden and Opel divisions used a different jack. Notice that they modified the data timing (160 baud rather than 300 and 8291 rather than 9600) so you couldn't simply use a Maxwell level shifter and talk to it with a standard Rockwell RS232 port. It takes a bit more ingenuity to plug the ALDL ECMs into a PC.
GM suffered from the same division rivalry that killed British Leyland. ALDL had a lot in common with the workers milling around after the curse at the Tower of Babel. Vehicles in the same nameplate using engines and controllers from other divisions spoke a slightly different dialect or completely different language from others. It must've been a special kind of nightmare for the EEs at Bosch, or Vetronix, or HP to build and program the Tech 1.
Pre-OBD II Ford/Lincoln/Mercury EEC I-IV vehicles were the same kind of nightmare. Chrysler was a similar mess. The other car manufacturers were similar. VW, Audi, Porsche, BMW, Benz, Vauxall, ... the list goes on.

OBD I is not an SAE or ISO or IEC or ... standard. California passed legislation requiring 1991 and later California Emissions Certified vehicles provide specific onboard diagnostic information in a specific format to CARB (California Air Resources Board) emissions testing stations. This was called OBD I. Outside of California emissions equipped vehicles OBD I did not exist and prior to the 1991 model year OBD I did not exist in California.

There were some bastard not-quite OBD II and not quite older spec orphans for the 1995 model year. Every manufacturer had them.
The US Federal government, Canada, and European OBD II specs superseded the CARB OBD I standards starting in the 1996 model year.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; 09-19-2021 at 05:20 PM.
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Old 09-19-2021, 05:16 PM   #9
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Re: Problems running at operating temperature

Back to the problem at hand.

Are the injectors spraying fuel while cranking after it dies on you?
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.
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Old 09-19-2021, 05:43 PM   #10
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Re: Problems running at operating temperature

Doesn't matter how many words you write, '88 is OBDI. OBDI the manufacturers did it however they wanted. OBDII is when it was standardized for every vehicle to be read by the same scanner.
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Old 09-19-2021, 06:28 PM   #11
hatzie
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Re: Problems running at operating temperature

Quote:
Originally Posted by Just call me Sean View Post
Doesn't matter how many words you write, '88 is OBDI. OBDI the manufacturers did it however they wanted. OBDII is when it was standardized for every vehicle to be read by the same scanner.
I was a young Electrical Engineer still in school in 1988. Where were you?

Some history never hurt anyone.
GM computer diagnostics in 1988 were called ALDL by General Motors. Look at the service manuals.
The early Ford stuff was called EEC... I, II, III, and IV.
I doubt you'll find mention of OBD I in any 1991-1995 period literature outside of CARB emissions testing books and possibly internal automaker docs in reference to CARB standards.

Nobody in 1988 had heard it being called Onboard Diagnostics or at least outside of the California legislature. Calling anything before 1991 OBD I doesn't make it OBD I. An OBD I standard did not exist til 1991 and then only in California. Not sure when they passed the legislation but it was likely in 1990.

OBD II is a legislatively prompted industry standard. The actual legislation was a done deal well before the drop dead date in 1996. The North American governments gave SAE and the major automakers til 1996 to produce a standard for onboard automobile diagnostics and implement it. It was called OBD II because CARB had already named their California version OBD I in the 1990 legislation. I believe the EPA administered the federal government end of things in the United States. Not sure what Ministry it was in Canada but they have one.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; 09-19-2021 at 06:50 PM.
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Old 09-19-2021, 06:58 PM   #12
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Re: Problems running at operating temperature

And World War 1 wasn't called that either at the time, not until World War 2. Times change. So not sure your point. And since the on board diagnostics (OBD) is identical on an '88 and a '91 I still don't get your point. Maybe it wasn't called it then but it's definitely called it now.
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Old 09-19-2021, 11:48 PM   #13
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Re: Problems running at operating temperature

EGR valve; replace it. I now recall a friend having a similar problem and I looked at the truck myself. All seems well and good and the engine dies when warm. It's a freaky thing but I'll bet that is your problem.
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Old 09-20-2021, 11:50 AM   #14
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Re: Problems running at operating temperature

Before you go throwing money away on new parts that won't last like the old ones, and possibly replace perfectly good parts, test test test.

Start with the Coolant Temp Sensor. It's in the intake manifold. Testing instructions are here: http://67-72chevytrucks.com/vboard/s...d.php?t=425788

If that's good, check for fuel and spark when it dies. Fuel pumps die slowly or intermittently, but rarely when the engine is hot. The pump is in the tank 15 feet away. Engine heat has nothing to do with the fuel pump dying. Pressure test would be correct if it sputtered or had no power.

In closed loop, the ECM is relying on all the sensor data, so it's likely a sensor or electronic piece that's failing. All are easy to test or see data with a scan tool. MAP, TPS, O2, etc.

The ICM under the distributor is well known for dying in the heat especially if heat sink compound wasn't used or not adequately. Just because you replaced a part doesn't mean the new part isn't DOA. Many new parts are junk, especially the cheap ones. Stick with Delco or Standard if you can.

EGR may be to blame as well, but you can test it before throwing money away at it. You also need to get the correct one. Info here: http://67-72chevytrucks.com/vboard/s...d.php?t=549711

You can test the EGR with a vacuum pump.
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Old 09-23-2021, 08:52 PM   #15
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Re: Problems running at operating temperature

High idle and then dies when hitting the gas would make me look for a vaccum leak.
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Old 09-30-2021, 11:08 AM   #16
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Re: Problems running at operating temperature

Sorry I have been gone for a while. I had to take a turn at having Covid. I guess I can't say China hasn't given me anything anymore. LOL

I haven't had a chance to try anything with my truck yet. Before covid I did replace the ignition Control module under the distributor cap. It didn't make any difference. It did the exact same thing.

The EGR Valve is good. It holds a vacuum like it should.

After it dies, it still has spark and the fuel seems to flow normally from the injector. By all rights, it should run after it dies while hot.

I'll run a coolant temp sensor and TPS test hopefully this weekend if I have the strength to do it. I'll also pull codes as well. I'll let you know.

Thank you for all the great responses.
Kevin C
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Old 09-30-2021, 02:48 PM   #17
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Re: Problems running at operating temperature

Might be a weak coil.
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