'97 5.7 Vortec no start - any ideas?

I have a 97 Tahoe with a 5.7 vortec and a sudden no start condition. On a quick trip to the store I came out to a truck that cranks and seems to have spark, but won't run. I have fuel pump pressure at the rails and I have no DTCs showing up on my Autotap scanner. The motor has 105K and has been running good up till now. Symptoms are similar to my experiences with an ignition module on an older motor going bad, or a timing chain jump. I get some firing, but it seems like the timing is off as it kicks back and sometime blows out the intake.

Any ideas? Should I look at the timing chain or maybe the crank position sensor? Is there a ignition module or is it an integrated part of the engine computer?

Thanks

Steve

Today's update - still hosed. I went ahead and replaced the ICM to no avail. I measured Fuel rail pressure at #65 which seems OK. I pulled a plug wire and checked for (and have) good spark. I opened the Dist. cap and checked for excessive play or cap cracks etc. - nothing found. I then put a timing light on #1 and it seems to be firing real close (like 3-5 degrees BTDC) based on the balancer mark. The engine cranks and seems like it's a little out of time, but I'm having a hard time believing a a timing chain slip at 105K, and it appers the spark is close to TDC.

Anyone know what to look for in a bad ECM/PCM? I know they are rarely the problem, but I do wonder when I don't see any DTCs and typically there will be a few historical events with frames in there when I check.

Any input would be appriciated.

thanks

you sure you have gas in the engine? cause you know you have spark, and only need 2 things, gas and spark. I think that the fuel delivery isn't making it for some reason. Sorry If I cant be of more help, I have a 5.7 but its carb'ed which makes it a little easier for me to know when it has gas or not.

Thanks for the reply. I think I have gas, well...., I mean the truck has fuel and it's getting to the rails. I haven't done a fuel pressure leak down test yet, but I can hear the pump come on and it doesn't keep cycling as I would expect with a stuck injector or other leak. I've changed plugs and they were wet, which further supports the fuel getting there.

There's Fuel, Spark, Compression and last but not least, Timing needed to bring it all together. That's where I'm concerned right now. I've got spark, I've changed the ignition module and put a light on it and it seems spark timing is OK. What I can't tell, is if the fuel is getting to the cylinders at the right time and in the right amounts. I have #65 fuel pressure at the rail with the key on, but that's about as far as I can go without manuals or some assistance.

Maybe time to let the dealership do their thing.

Thanks

Thanks for the reply. I think I have gas, well...., I mean the truck has fuel and it's getting to the rails. I haven't done a fuel pressure leak down test yet, but I can hear the pump come on and it doesn't keep cycling as I would expect with a stuck injector or other leak. I've changed plugs and they were wet, which further supports the fuel getting there.

There's Fuel, Spark, Compression and last but not least, Timing needed to bring it all together. That's where I'm concerned right now. I've got spark, I've changed the ignition module and put a light on it and it seems spark timing is OK. What I can't tell, is if the fuel is getting to the cylinders at the right time and in the right amounts. I have #65 fuel pressure at the rail with the key on, but that's about as far as I can go without manuals or some assistance.

Maybe time to let the dealership do their thing.

Thanks


So it seems like it has jumped time?
What might have happened is the distributor gear may be severely worn causing your problem......I am baseing this on your description and diagnosis..so bear with me as I go out on a limb here...
Pull the distibutor out ( after you mark the rotor position) and inspect the teeth on the gear...are they worn and the edges thin and sharp?...I had one doing the same thing you described and that is what I found..replaced the gear and they drove off happy....
Unfortunately you cannot check timing on those engines like we did in the past...so I wouldn't put much faith in the crankpulley/timing mark diagnosis.

I ended up towing to the dealership. My surprise when they diagnose an internal crack and corrosion in the dist. cap. I'm still beside myself, I looked at the cap and rotor and they seemed like any cap and rotor that had some miles, some pitting was all I saw. Heck, the motor is supposed to go 100K before a tuneup and I had replaced the cap and rotor at 60K (NAPA Echlin). Anyway, $200 later a new cap and rotor and it's running fine. I sure hate the idea that I missed that, (especially since I looked at it) but I guess that's what the right equipment will do. I still don't understand the sudden problem with no previous hesitation, gas mileage problem or hard starting. Just all the sudden, no start. Cross firing does explain the symtoms similar to timing.

Live and learn, replace everything you can before you take it in. I'm just glad I did plugs or they would have done those too.

Thanks for the help and hopefully someone else will learn from it.

Thanks

Steve

I have had the same problem with my 1996 Tahoe, it was indeed the cap... but it was not from corrosion, but from an internal crack as you described. The spark would jump from one cyclinder to another. It has done this to me a total of three times. Here is what I have found to be the root of my problem. THE POSITIVE BATTERY CABLE! Awhile back I had a leaky battery. I replaced the battery and cleaned the POS cable. After a few months I was having voltage problems where the truck would just stop running like I had turned off the key. The POS battery cable had corroded. I would just jiggle the POS cable and it would come back to life. It seems that this fluctuation in voltage has caused several problems from fuel mileage, and computer controlled ignition. I finally broke down and bought a new POS cable and I have had no problems since. What I’m getting at is that you might want to check your positive battery cable for corrosion, to circumvent any further problems.