1991 C1500 5.7L that wont start

[rkthev]

I have a 1991 C1500 5.7L that wont start. The truck had not been used for several years. I was able to get it started and it ran fine a couple times. Then the next weekend I went to start it and it would not start. It was backfiring some, so we chacked the ignition and found some corrosion in the distributer cap and wires. I replaced the cap, rotor wires and plugs. It seemed to solve the backfire but still no start. It has good spark which jumps across an HEI psark tester. The timing is good. It has a good flow of fuel from the injectors, but it just cranks and does not seem to even try and start, unless you floor the accelerator and put it in flood mode, it seems to kick over a little but no start. So far the cap, rotor, wires, plugs, ignition module, MAP sensor and coil have been replaced. The temperature sensor, TPS and oxygen sensor test good (reads correct value using WINALDL). Even though it has good spark and fuel it doesn't start. Suspecting fuel being too rich wedisconnected the injectors and tried some starting fluid and it does not start with it either. We are out of ideas right now. Any suggestions?

[oldscsc]

You need fuel, spark, air, compression, and timing.

 

TBI systems aren't particularly picky when it comes to fueling. If it won't run on starting fluid, fueling is probably not the issue.

 

If you have a clean, blue spark, your ignition system is working well.

 

Have you done a compression check?

 

Is there a sensor that tells the PCM where the engine is at in its rotation, i.e. a crankshaft or camshaft position sensor?

 

Is the PCM throwing any codes?

[rkthev]

No position sensors on this engine. Only code was a high MAP sensor. Its been replaced, code cleared and has not returned. I assumed maybe a backfire set that code. Compresion check is next. Truck is 100 miles away so I get limited by the tools and test equipment I remember to take with me. Pretty confident compression is ok, as I dont see it changing from the trucking running pretty good, being turned off, then setting a week and then no start. Also will remember to take fuel pressure gauge just to verify it,

[oldscsc]

Fuel pressure and compression checks will yield useful information. Are you sure the distributor isn't 180 off? Don't want to miss the little things.

[rkthev]

Yep, sure the distributor is not 180 off. Be a week or two before I get back up there to check compression.

[rkthev]

Just updating this, as I hate when threads end without ever saying what the resolution was. My compression check found a few cylinders with issues. Took the valve covers off and found 3 bent/broken pushrods. After replacing the pushrods, and turnng the engine over by hand to set the second set of valves I got resistance, and found two intake valves that would not open. So the heads are in the shop now. Report was 4 bent valves. Still nit sure why it ran fine one day, and a week later would not start. I assume the back firing while trying to get it started caused the pushrod and valve issues. Thanks to those who replied, hopefully this truck will be running in the next couple weeks...