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Username Post: URGENT PROM 85 ERROR - I'm stuck in Mexico!!        (Topic#287680)
Forum Newbie
Posts: 11

Reg: 09-29-12
09-29-12 09:11 PM - Post#2274940    

Hi! we're a British couple with a Canadian-born 1992 Chevrolet g30 1 tonne van (5.7 auto) currently in Palenque, Mexico and supposedly headed for Argentina!!

We have an urgent problem as we cannot drive far due to a fault - the vehicle starts fine but once warm it will gradually loose power, struggle and come to a stop. if we restart the vehicle immediately it will work fine for a few hundred yards before beginning to stuggle again. The problem gets progressively worse the longer we drive but for the first 20-30 minutes each day it is fine!

Here is some background: driven from Canada, no problem (except a new shield, exhaust etc.!). 2 days ago we parked after driving as normal but car would not start after a 10 minute stop. Local mechanic identified faulty FUEL PUMP and dropped the tank and replaced it. Started fine and we drove up a big steady hill for 50 minutes then around a town. Van worked fine.

After 2 days parked, 15-20 minutes down the road the loss of power started uphill and we grinded to a halt some 5 minutes later. Got towed to the next town and limped in. Got new fuel (better octane fuel - 91 (the best in Mexico!) but we had previously been running 87 (and also in US and Canada with no problem). After refuelling started and drove fine for 10 mins.

Next day, after 10-20 minutes of good, normal operation the same loss of power again and we had to limp in to the next town. If turned off it would then go well for a few minutes before gradually dying again.

I have since: replaced air filter, checked fuel filter, visually inspected for leaks, put some injector cleaner in, driven around, cleaned spark plugs (they were all sooty black an they probably are again now), partly dismantled the TBI to inspect the fuel injectors (seem OK when just started until problem starts), and checked that there is fuel coming in.

I have not checked fuel pressure (need to find a mechanic on Monday). I assume the mechanic who replaced the FUEL PUMP put the right one in but I do not know. I saw it briefly (it was 9pm) and it looked the same. It is strange that the problem has developed 40-50 miles after a new pump but it seems to be working). We seem to be using more fuel than usual.

Fault codes read 44 (lean mixture)
fault code 85 (PROM error)

If anyone can suggest likely cause please help. i have a haynes manual, an adjustable wrench and basic Spanish :P

Parts are hard to find, as are mechanics with full facilities and no Chevrolet dealer nearby or breakers yard that I know of. Need to identify the problem asap as we have nowhere to stay!

thank you so much and sorry for the length of this !


Posts: 674
Age: 61
Loc: Western, N. Carolina
Reg: 02-01-05
09-30-12 04:47 AM - Post#2274970    
    In response to bob5513

I did find this, sounds like your engine computer is toast.

Auto Systems and Repair
GM OBD Code 85
OBD I Code 85 - PROM error

If the ECM detects an internal fault with the PROM code 85 will set. The PROM is a special "chip" that is installed in the ECM, based on the particular vehicle configuration.

Fault Code Description

85 - PROM


Engine may not start
Poor engine performance

Common Problems

Internal fault with PROM
PROM incorrectly installed in ECM

The lean code could be caused by the prom code which should be fixed first.

1959 El Camino
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2004 Z71
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Forum Newbie
Posts: 11

Reg: 09-29-12
09-30-12 08:14 AM - Post#2275025    
    In response to DEI8FAN

thank you. I reset the computer (by taking the battery terminal off) and although I still had a problem (lack of power, some knocking/pinging maybe, odd misfire and generally no go) it hasn't re-registered any fault codes...very tough to find a new PROM down here.

We will get a fuel pressure
test done tomorrow.

"5th Year" Silver Supporting Member
Posts: 1777
Loc: SE North Carolina
Reg: 08-19-04
01-02-13 07:03 PM - Post#2303485    
    In response to bob5513

Bob, just saw this (it three months old) and wondered how things worked out? Hope they did and that you reached your destination without too much additional hassle. Don

Subject Matter Expert - Senior Member
Posts: 3863
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
01-04-13 03:05 PM - Post#2303971    
    In response to Highlander1

He started another thread.

  • bob5513 Said:
Then I accidentally knocked the connector joining to the Igntion control module and it sporadically worked.

Problem was just those metal ends inside the 4 pin plug has been loosened with the removal of the plug!! They looked fine, no corrosion and I didn't spot them at first check. I just pinched them tight and she runs great!!!!!!!

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


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