1991 454/4L60E loping idle, no power, codes

[EDZIP]

Truck is a 1991 Chevy 3500 step van, 454/4L60E 16,000 miles (current volunteer fire department vehicle - trying to help them)

Loping idle, no power, no check engine lights. Bucks and shuts down when you try to take off, starts right up again.

The local Chevy dealer said the MEMCAL was bad, they replaced the 16154301 ecm with a reman 16147060 and used the stock AWAU MEMCAL..still ran as described above.

Went over there today, used a moates adapter and tried:

AWWH runs- no change
copied the original AWAU BIN (hard to find - copy attached) to a prom - runs- no change
tried MEMCAL AWUC (1992 3500 454/auto) that I have - runs - no change

Then for the heck of it tried an aftermarket ignition module I had in my tool box...started, and "idled nicely for a minute or so"..BUT then reverted back to crappy idle etc. It had a 369 module in it.

Loaned my OBD1 OTC Nemisys scanner out picking it up tonight and will data log tomorrow...but right now...no MIL lights at all.

Have any suggestions before I head back over.

[Fast355]

Truck is a 1991 Chevy 3500 step van, 454/4L60E 16,000 miles (current volunteer fire department vehicle - trying to help them)

Loping idle, no power, no check engine lights. Bucks and shuts down when you try to take off, starts right up again.

The local Chevy dealer said the MEMCAL was bad, they replaced the 16154301 ecm with a reman 16147060 and used the stock AWAU MEMCAL..still ran as described above.

Went over there today, used a moates adapter and tried:

AWWH runs- no change
copied the original AWAU BIN (hard to find - copy attached) to a prom - runs- no change
tried MEMCAL AWUC (1992 3500 454/auto) that I have - runs - no change

Then for the heck of it tried an aftermarket ignition module I had in my tool box...started, and "idled nicely for a minute or so"..BUT then reverted back to crappy idle etc. It had a 369 module in it.

Loaned my OBD1 OTC Nemisys scanner out picking it up tonight and will data log tomorrow...but right now...no MIL lights at all.

Have any suggestions before I head back over.

I would check two things. Fuel pressure and the TBI base gasket. The base gaskets are known for failing causing a vacuum leak in the IAC/MAP sensor area. The little piece of rubber fuel hose in the tank between the pump and sending unit is also prone to ethanol attack and splitting open causing low fuel pressure. I think you will likely find your issue if you check both.

Also seen similar issues with bad/corroded/dirty grounds and ground straps.

[EDZIP]

I would check two things. Fuel pressure and the TBI base gasket. The base gaskets are known for failing causing a vacuum leak in the IAC/MAP sensor area. The little piece of rubber fuel hose in the tank between the pump and sending unit is also prone to ethanol attack and splitting open causing low fuel pressure. I think you will likely find your issue if you check both.

Also seen similar issues with bad/corroded/dirty grounds and ground straps.

Thanks for the prompt response, I have have SBC throttle body gaskets...but assume the 454 will have a larger bore diameter...what fuel pressure am I looking for 12lbs +/-?

May just get the water bottle out for the gasket check..

Was going to mention the ground concern..ran into that problem once.

[Fast355]

Thanks for the prompt response, I have have SBC throttle body gaskets...but assume the 454 will have a larger bore diameter...what fuel pressure am I looking for 12lbs +/-?

May just get the water bottle out for the gasket check..

Was going to mention the ground concern..ran into that problem once.

454 applications I have messed with have larger throttle bodies. Never gotten to play with a 454 P30 chassis, but I would assume it is similar to the motorhomes I have messed with. As far as I know nothing before 1994 had the high pressure fuel system. Typical fuel pressure is 10-13 psi.

[EDZIP]

454 applications I have messed with have larger throttle bodies. Never gotten to play with a 454 P30 chassis, but I would assume it is similar to the motorhomes I have messed with. As far as I know nothing before 1994 had the high pressure fuel system. Typical fuel pressure is 10-13 psi.

Thought the 454 throttle body had the same bolt pattern as the 5.7...just larger bores?

Could also use a pin out for the 16147060 ecm if someone has it...may as well tap into the ecm grounds while I'm at it.

[1BadAction]

454 TB is the same bolt pattern.

Without a scan tool it's hard to say anything. I will say, they (those ECMs) add nearly 20 degrees of timing in cold weather, so if the CTS is shot it will do just as you describe, along with backfiring and running pig rich.

[fastacton]

Yes, a 454 throttle body has the same bolt pattern, but larger bores and overall larger footprint. You said this has a 4L60? are you sure it's not a 4L80? There are diagrams for the 7060 in this forum http://www.gearhead-efi.com/Fuel-Inj...Information-85. It looks like AWAU has been superseded by BAMS, I looked around and I don't have that one, though I do have several 7060 ECMs. The datalog might be a big help in troubleshooting this.

[EDZIP]

Yes, a 454 throttle body has the same bolt pattern, but larger bores and overall larger footprint. You said this has a 4L60? are you sure it's not a 4L80? There are diagrams for the 7060 in this forum http://www.gearhead-efi.com/Fuel-Inj...Information-85. It looks like AWAU has been superseded by BAMS, I looked around and I don't have that one, though I do have several 7060 ECMs. The datalog might be a big help in troubleshooting this.

10-4 "typo" 4L80e

Thanks (1BadAction "also") for the link..just picked up my OTC scanner for tomorrow.

Need to install the TBI fuel pressure adapter to check pressure, so may as well get a fuel sample while the lines are off. I'll report back tomorrow and look for a copy of BAMS tonight.

thanks guys..

[EDZIP]

I would check two things. Fuel pressure and the TBI base gasket. The base gaskets are known for failing causing a vacuum leak in the IAC/MAP sensor area. The little piece of rubber fuel hose in the tank between the pump and sending unit is also prone to ethanol attack and splitting open causing low fuel pressure. I think you will likely find your issue if you check both.

Also seen similar issues with bad/corroded/dirty grounds and ground straps.

Looks like you are the winner..the vehicle just came back from a Chevy dealer that replaced the ECM but couldn't locate the AWAU memcal. They returned the truck to the fire department in the same non running condition (with a very hefty bill). Assuming the dealer had their caca together..I burned several proms and tried another memcal....same condition.

Go over there this am with my OTC Nemisys that was previously loaned out..and it won't communicate via the OBD1 connector..(going to start another thread on this problem). So the only thing I can do is check fuel pressure...Gets a burst of about 2-3lbs! Couldn't get my TBI adapter to fit so I just rubber clamped it at the throttle body inlet and before the fuel filter (both locations) with and without return line clamped...same thing 2-3lbs. Fuel pump on order!

Thanks

[fastacton]

That'll do it! I'd bet there was never anything wrong with the ECM, the dealer might need to apologize and maybe refund some money. For the commo problem, maybe try a different VIN that also had a 7060 in it (assuming continuity between the ALDL and ECM)?

[1BadAction]

Looks like you are the winner..the vehicle just came back from a Chevy dealer that replaced the ECM but couldn't locate the AWAU memcal. They returned the truck to the fire department in the same non running condition (with a very hefty bill). Assuming the dealer had their caca together..I burned several proms and tried another memcal....same condition.

Go over there this am with my OTC Nemisys that was previously loaned out..and it won't communicate via the OBD1 connector..(going to start another thread on this problem). So the only thing I can do is check fuel pressure...Gets a burst of about 2-3lbs! Couldn't get my TBI adapter to fit so I just rubber clamped it at the throttle body inlet and before the fuel filter (both locations) with and without return line clamped...same thing 2-3lbs. Fuel pump on order!

Thanks

I wouldn't pay the dealer a thin dime, fuel pressure is one of the FIRST things you diagnose on an EFI vehicle... Sounds like the typical "tech 2 techs" though. If a computer doesn't tell them whats wrong they don't know what to do.

[EDZIP]

I wouldn't pay the dealer a thin dime, fuel pressure is one of the FIRST things you diagnose on an EFI vehicle... Sounds like the typical "tech 2 techs" though. If a computer doesn't tell them whats wrong they don't know what to do.

Agree 100%!

[buddrow]

Agree 100%!

We call them types "shotgun mechanics". They just stand back and throw parts at it and hope they hit with one of them, charging customers for their ignorance(the techs ignorance not the customers). I worked for a dealer here and the foreman had the big wall size tool box and it had more new/good parts in it than tools. Disgusts me.just my .02.

Buddrow

[steveo]

dumbass cart before the horse stuff is so common;

recently worked with a 4 banger car that wouldn't idle or run under load at all, like a total bag of crap. it had every o2 sensor, maf, map, torque converter, bunch of crazy things replaced based on a bunch of hair-brained theories.

i popped the oil cap off with it running and it flew 5 feet in the air. pull spark plugs, flashlight, find hole in the piston