New guy

[J3920]

Came across this site while trying to sort out issues with my 1992 GMC K3500 7.4L farm/work/daily driver flatbed truck. Currently waiting on a cable so I can see if I am smart enough to capture senor data and isolate the issue, which is Code 45, rich O2. A code I could only pull after replacing the computer which would not give any codes when jumpering A&B terminals of the ODB1. After replacing it sadly I admit to throwing parts at it, O2 sensor, temperature sensor, MAP, rebuilt TBI, distributor, coil and all grounds cleaned. At this point everything has been replaced except the fuel pump and chip in the computer. Really hoping scan data will point out what is causing the problem.

[1project2many]

Welcome! I think you've found a great resource to help troubleshoot the problem And you're not alone in playing parts roulette. Even trained techs do it once in a while.

The ECM will set code 45 when the voltage reading from the O2 sensor is consistently high despite the ecm trying to reduce the amount of fuel being delivered. The O2 sensor voltage goes up when the exhaust side of the sensor sees less O2 than the air side of the sensor. Factory testing will follow a path from most likely issue to least likely issue. Issues like coolant temperature sensor reading incorrectly or MAP sensor reading incorrectly or throttle position sensor reading incorrectly can cause a rich condition without setting a code for the sensor. Less common issues include the fuel pressure being too high and the EGR valve not closing properly. They do happen but not very often. If none of these components can be identified as the culprit, the diagnostics usually bring you to the ecm. Back in the day ECM and chip failure was considered least likely to cause an issue. But that was 30 years ago!

I'd suggest starting a separate thread in the Fuel Injection forum for additional assistance with this.

[MO LS Noobie]

Another thing to check is battery voltage getting partially shorted to the 02 wire. This will skew the voltage high prompting the computer to lean the mixture out. It feels like it is running out of gas. How does the truck run, from coldstart, idle, and running down the road? Does it set the code all the time or intermittently? Just throwing some suggestions out there.

[J3920]

Another thing to check is battery voltage getting partially shorted to the 02 wire. This will skew the voltage high prompting the computer to lean the mixture out. It feels like it is running out of gas. How does the truck run, from coldstart, idle, and running down the road? Does it set the code all the time or intermittently? Just throwing some suggestions out there.

Things I failed to mention, I have checked the wiring for shorts, grounds, ect. and cleaned the grounds since it was noted as a potential cause. It does not act like it is running out of gas in fact it is so rich you can hardly stand to be near it. Cold start has always been, literally, hit the key for 2 seconds, then the second time it fires up almost before you can let go of the key. Although now it is taking a couple of seconds before it starts. Idle is the same as it had been since I got the truck several years ago but it now has an intermittent misfire about a minute after starting that clears quickly. Running down the road it acts normal for about a 1/4 mile then it starts to randomly miss, stumble and lose power then the light comes on. Every time I have cleared the code, the next attempt to drive it the code is reset. The code 45 is the ONLY thing that has been consistent since this problem started and replacing the computer.

I have also questioned the reman computer, the OEM was replaced because the SES light would come on but I could not pull any codes. The light stayed on solid, remove the battery and then it would give the 12 code. Run the truck and again the SES light would come on but it would still not give any codes. Again a solid steady light. That is when I replaced the computer and was able to get the code 45.

I tested the fuel pressure and it is low, 7.5 lbs. The pump will be replaced sometime this week, temperature permitting, but I cannot see weak pump pressure causing it to get too much fuel. Lean I could understand but not rich. The only other thing not changed or tested against known good is the chip itself in the computer. Someone at sometime replaced it with a Stage 2 Hyperchip, could that be the problem?

BELIEVE ME, I am open at ANY and ALL suggestions.

[1project2many]

It does not act like it is running out of gas in fact it is so rich you can hardly stand to be near it.

Are you getting black smoke at idle or while driving? Or just the smell of fuel?

Is there any information on the Hypertech chip? Do you have or know someone who has tools to read the chip? Hypertech chips are usually very mild but it's possible the chip is for a completely different engine. If the truck is mostly stock it might be a good idea to locate a copy of a stock calibration.

[J3920]

Are you getting black smoke at idle or while driving? Or just the smell of fuel?

Is there any information on the Hypertech chip? If the truck is mostly stock it might be a good idea to locate a copy of a stock calibration.

No smoke just horribly rich gas smell, to best of my knowledge the truck is stock. The Hyperchip tag has a date of 1996, P/N:122072, S/N:528420 and a seperate stamp with Delco, AXRB, 2285.

I looked up that Hyperchip part number and it stated it was a Stage 2 thermo chip for use with 91 octane and 160 thermostat. I did not know about the chip until this problem developed but I had replaced the thermostat when the water pump went out to a 180, simply because this engine runs so darn HOT. It has never had 91 octane in it since I have owned it and I am sure the guy who I got it from never used it either.

I have been trying finding a stock chip but to date have had no success. Any suggestions on where to look?

[MO LS Noobie]

Try the hard reset. Disconnect the battery terminals and short them together for a couple of minutes. I would also unplug your oxygen sensor(s). Then hook the battery backup and when you start it will run on the base tune, and with the oxygen sensors disconnected it will not tried to adjust the fuel mixture. If it runs better and you don't smell the fuel out of the exhaust, then your tune program is okay. Then turn the engine off and plug the oxygen sensors back in, clear all codes, and see what it does.

Another thing I would look at real closely is the chip that you changed over when you replaced the PCM. Make sure there aren't any bent pins.

[J3920]

I checked the chip for any bent or burned pins before installing it so I am confident that is OK. I will do the reset, test it and report back although it will be the weekend before I will be able to work on it.

Thanks for the test tip.

[J3920]

Many thanks to those who responded, I finally ended up taking the truck to have the fuel pump replaced. In times past I would have done that myself but time and surgeries have put an end to that. While they had it they also looked and found found the code 45 problem, it was the aftermarket Hyperchip. Did away with it and the truck is now running fine. I had questioned if it could be the source of the problem as soon as I found it but I did not realize the Hyperchip was an addon in between the the OEM chip and the board. Had I known I would have removed it.

Thanks to all who offered help

[MO LS Noobie]

Glad you got it figured out.

[1project2many]

Yes! Very happy to hear it helped. Thank you for taking time to post the conclusion.