96 C3500 5.7 Hard Start

[rsmith8411]

Over the last few weeks my trusty ol' 96 C3500 2WD 5.7L (324k miles! and strong) has started having trouble starting cold. It does fine when warm but mornings are getting rough on it, even though it is in a garage overnight. The battery and starting system are strong. There are no codes being thrown (I have an Actron code reader and there are no codes lighting the SES light nor are there any "hidden" codes). Here's what I've done:

-new fuel filter
-new distributor cap/rotor
-relatively new plug wires (< 1 year)
-fuel pressure tested (60 psi with key on/not running; 52 psi running; pressure drop almost nothing in 5 minutes (about 5 psi an hour after shutting off))
-coil resistance tested good (source for specs: AllData)
-pulled 2 spark plugs and inspected: look good
-checked engine temp sensor at PCM with code reader: reads what it should (60 F mornings and higher as appropriate after running)
-checked PCV

When it does crank it sputters for just a moment and then runs fine.

Also came across a TSB about crankshaft position sensor advancing spark too much during cranking but I don't see any engine codes. I don't have any backfiring or other symptoms described in this TSB, though.

Any ideas on what to do next?

[jamesslcx]

rsmith, so you say 5psi an hour after shutting off, seems like it should hold more pressure than that for longer. I forgot the specs but that seems off. That's a lot of mile seems like you take good care of it. Good luck.

[rsmith8411]

I appreciate your interest and help. The Haynes Manual says "should not drop more than 5 psi within 5 minutes". Mine is plenty good according to Haynes, but my concern is that I have a fuel injector leaking and flooding a cylinder. 5 psi in 5 minutes isn't bad enough to replace a fuel pump, but it may be enough to flood a cylinder.

How do you chase down a leaking fuel injector? Thoughts?

[jamesslcx]

rsmith8411. that's a good point about the fuel pressure, you could be onto something with that injector. If it's leaking in the cylinder you could maybe pull the plugs and look for one that's wet with fuel. How's your mileage/ Is your tailpipe black? Good luck.

[rsmith8411]

Solved: it was the fuel pump. It got worse quickly since I first posted. Fuel pressures gradually dropped into mid 50's, which I would have thought to be close enough to the spec of 60 but I was wrong. Got to where it wouldn't hit a lick. New fuel pump pressures look to be in the same range as the old (slightly higher -- upper 50's) but something is different because it starts and runs great now. I also replaced the fuel pressure regulator and crank sensor along the way but that made no difference.

I'm puzzled why I couldn't see more difference in the old and the new fuel pump when reading the pressures, but there it is.

[jamesslcx]

Rsmith, glad you figured it out and thanks for the valuable lesson, evidently a small amount of pressure means a lot.

[777stickman]

What brand of fuel pump did you put in? Was it matched to your VIN?