Used to run great, but now won’t start
 

Hi all,

I have a 1999 GMC Suburban, 5.7L with 315K miles. I bought it new, took good care of it, and until a couple of weeks ago, could always rely on it starting and running fine. My son has been using the vehicle lately and went to start it one morning and it would crank fine, but not fire. I thought it was a fuel filter problem, but when I tried to replace it, I broke the fuel line. A friend repaired that for me and managed to get the thing to start and run, but it ran rough and died if it idled. I decided to clean the throttle body, and ever since, it won’t start. Cranks great, just won’t fire. I tested the fuel pressure and it is 60psi. Tested for spark on a couple of cylinders and got spark. I suspect maybe there is an electrical problem; we live in a rural area and have various critters that seem to like to chew things. But I don’t know how to test. For instance, is it possible to have an electrical failure in the fuel injection system? If so, how can I test that? Or is it something else? Any help would be greatly appreciated. I know this vehicle has 315K on it, but I was hoping to get a couple more years (until my son gets his own car). Thanks!

How did you test for spark?
Use a stethoscope or screw driver and see if they click.
Noid light?

I used an inline spark tester. Pulled the wire off the plug, inserted the tester between the wire and the plug. Rhythmic flashing when my helper cranked the starter. Same result when I tested another cylinder.

What color was the spark? Can you hear it crack?
Even if the volts are there does not mean the plugs are firing.

I wonder if the Idle Air Control valve got flaky then failed.

What did you clean the throttle body with?
If it was not MAF cleaner, and it got on the MAF's thermistors, then it could run rough, and possibly not at all...
https://www.rockauto.com/info/983/98...ay_1__ra_p.jpg

In another forum (I was desperate), a member suggested that, even though I have spark, it may not be strong. He suggested replacing the distributor cap and/or the rotor. I replaced both (as I said, I was desperate). It started right up! I have been cranking this thing and recharging the battery for a couple of weeks without so much as a cough. Once the parts were replaced, I just turned the key and it roared. I hope this helps someone else.

You were right. I replaced the distributor cap and rotor and it started right up.

Also, I meant to say Thanks! to all who replied. I appreciate your input.

Glad you got it running.