My 1990 K5 has been having issues with backfiring for the past couple of months. Originally, I had a trouble code for the EGR valve/solenoid and got the solenoid replaced, helped keep the backfiring down for a little while but it was back in a few weeks. It happens at highway speeds of 65-70 MPH, between 2000-2500 RPM's, under heavy throttle (going up a hill, trying to speed up to pass someone). The engine almost 'pops', cuts out for a split second and keeps going. This week, it started doing it several times after driving up and down several hills on the Merritt Parkway. Next time i took it out, the engine fully cut out/stalled going up these small grades/hills at only 25 MPH. I was pretty low on gas at the time, which makes me think that it has something to do with the fuel pump, could be not sending enough fuel to the engine and it's starving under high throttle. But it could be anyway, the truck sat for an extended period of time before I bought it, so plugs, wires, cap and rotor, etc. I'm looking for some help on what to look for that may be the problem. Thanks!
CK5
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Stalling K5
- Thread starter dj31499
- Start date
Fuel pump or the hose that connects the fuel pump to the module. Done.
But seriously, 90% percent of the time the only trouble a tbi chevy has is fuel pump or distributor.
rampage
3/4 ton status
IIRC a clogged catalytic converter can cause backfiring, someone else will need to either confirm or deny that. If so, then rent an IR gun from your local parts store to check it using step 6 here:
https://www.3geez.com/forum/3geez-accords/81802-how-diagnose-bad-catalytic-converter.html
https://www.3geez.com/forum/3geez-accords/81802-how-diagnose-bad-catalytic-converter.html
Can Can
Pusher Man
I can't recall if the early TBI units came with an in-line fuel filter. If so, did you change it out?
Start with the easy things first, brother.
Start with the easy things first, brother.
rampage
3/4 ton status
There’s a ‘pre-filter’ in the tank that consists of a sock before the pump. Then on the passenger side framerail just in front of the rear tire there’s the gas filter.
Can Can
Pusher Man
I knew about the sock in the tank, I just wasn't sure about the in-line filter. I do know of others who have had fuel supply issues due to plugged filters after running trucks that have been sitting for excessive amounts of time. OP's symptoms sound like a fuel starvation issue to me. Could be wire-related as well.
rampage
3/4 ton status
No doubt that the basic need to be covered after sitting for a while. Even wiring should be checked for signs of critters chewing on it - not that that’s his issue, but in general.
Would fuel starvation cause backfiring though?
Mine ran all kinds of bad with a split in-tank fuel hose. Smelled noxious at times, wanted to stall, bogged, backfired, or ran fine.
Injection does everything it can to keep the vehicle running. Because the fuel pressure isn't remaining constant with a split hose (if it's the issue, and depending on fuel level, slosh, angles, etc), the ECM has an impossible time controlling the injectors to the desired air-fuel ratio. That will lead to both over and under-fueling, possible fouled plugs, etc.
FWIW, autozone will loan out fuel pressure testers, so while some work to test, free to test. You can tell a split hose pretty easily by how fast fuel pressure drops when the key is turned to "run" and the pump primes. With the engine running, pressure below about 10PSI is indicative of a potential fuel system problem. 9-13PSI is GM spec, but seems pretty universal that TBI runs noticeably worse when it gets down to around 10PSI. I used the same tester before and after the inline filter to make sure the filter wasn't an issue as well, which it wasn't, after 10 years. (But very few miles over that time.) IIRC it lost something like .5PSI through the filter, which when talking the 43.5PSI TPI system, is not much at all.
Need to do as much diagnosis as you can. Any of the original in-tank fuel hoses are going to split in time though, they were not rated for ethanol.
