Need some help, ignition issue- I think

[steves1967]

My 97 K3500 454 died on me yesterday. I was pulling the travel trailer, had just come out of a stop sign and I was speeding up when it started popping and banging, I could hear it backfiring and popping through the intake as well.

Towed it home (thanks AAA) checked the obvious; none of the spark plugs are damaged so I figure I didnt break a valve. The rocker arms move so I didnt break the timing chain, changed the oil and cut open the oil filter- No metal in the oil or filter, checked to see if it has spark- and it does, I can hear the fuel pump running before start up.

Computer isnt showing any trouble codes either. Truck has 108,000 miles on it. What am I missing? Could it have jumped a tooth on the timing chain? Before I take it to the repair shop @ $127 an hour I'd like to do as much as I can to figure this thing out. It sounds like the timing is off when you crank it over. It'll crank but wont fire....

Thanks for any help!!!

[speedygonzales]

Don't assume the fuel pressure is correct just cause you hear the fuel pump running. Check the pressure. You could always squirt fuel in the intake while someone cranks it over.

[bwood]

If I'm not mistaken, two fairly common issues on that engine are the fuel pressure regulator and the coolant temp sensor. If the regulator failed, no fuel or too much fuel could be the problem. If the CTS (the one in the intake, doesn't have anything to do with the temp gauge) failed, the computer may think the engine is super cold and dumped a large amount of fuel and adjusted its timing accordingly. I would test the fuel pressure first as it should still run with a bad CTS, just not well. I don't know the spec right off hand, but a guess would be above 55 psi probably closer to 6oish as it is a MPFI. In your post you didn't mention if you actually had spark either, just that the plugs were ok. Do you have good spark?

[steves1967]

Yes i have a good spark. I'm going to check fuel pressure this afternoon. How likely is it that the timing chain jumped a tooth on the gear?

[ChevLoRay]

Before jumping to conclusions (and I understand your plight), check that fuel pump pressure. There are numerous posts on here that detail the pressure and the temps that are part of the parameters.

With only 108K miles, I'm inclined to believe that your timing chain is not the problem....well, based on my own feelings, that is.

[steves1967]

Alright, I've got 57psig of fuel pressure while the engine is cranking. With a scan tool would I be able to look at the timing as the engine is cranking?

[steves1967]

Compression test results:

Engine cold (obviously)
throttle blades open
Held key on for count of 2 (1 mississippi, 2 mississippi)

1- 150 2-155
3- 148 4-165
5- 155 6-160
7- 148 8-155


The plugs are now all black and smell like fuel, where when I fisrt started they were white/tan. Now what

[ChevLoRay]

So, have you had it started and running, since you started this thread? The only reason I can think of that would have a plug black and smelling of gas would be that they weren't firing.

[steves1967]

No it hasnt started since I began this thread. I think it's going to have to go into the shop, but I want to exhaust all the easier diagnostics so the shop doesnt duplicate my work and charge me unneeded $$$

[ChevLoRay]

If I was working in a shop, and a vehicle was brought in that would not run, there would be things that I would have to check....just for my own ground rules. The fact that you have done the investigative work that you did, would be good to hear. It would tell me that I wasn't dealing with some schmo that didn't understand the nature of the beast.

I think the unfortunate fact is that some of the things you have done, ostensibly to save some bucks, are going to be repeated at the shop of your choosing. It may be that you overlooked something simple. It may be that it isn't something simple and you didn't want to know that "that" was the problem. Don't feel bad. It's human nature. We want to hear the good and the bad, just not all of the bad....and not all at once.

Hopefully, it will be something simple and a total surprise. But, ignition certainly seems to be the starting (no pun intended) point.

Good luck. Let us know what develops.

[steves1967]

Working on it now! If the chain did jump a tooth wouldnt that throw a trouble code as the cam and crank position sensors wouldnt match up any longer??

[bwood]

Originally Posted by steves1967

Working on it now! If the chain did jump a tooth wouldnt that throw a trouble code as the cam and crank position sensors wouldnt match up any longer??

Probably. You did a comp test, did the cylinders/plugs smell like fuel? If not go to the parts store and get a "noid" light for your fuel injector plugs. This is a small light that you plug the injector plug into and it will flash with the firing of the injector. If you are not getting any flash, you problem is going to be a issue with the ECM seeing the engines rotation. I believe the crank sensor is responsible for this. In the Chilton manual, I belive they give the test proceedure for the crank sensor.

[steves1967]

All the plugs smell like fuel now and are probably fouled. When I first started this project the plugs were grey/tan... so it's definetly getting fuel