96 Tahoe - rough start when warm

[Adventurer_96]

New AC Delco plugs, air filter, fuel pump & filter, and O2 sensor in the past few weeks. The O2 sensor was yesterday but after I replaced it I found that after driving then letting the truck sit for an hour it took two cranks to get it to catch, at which point it ran fine. It felt like a fuel starvation from a carbureted engine, I guess you could say, but with a new pump I can't see it's a fuel problem.

I'll check the fuel pressure with a tester (I'm away from home and have to use a borrowed one) to confirm but I'm thinking ignition.

Before I get under the hood and start testing the coil, is there anything else to check out? I know I should replace the sparkplug wires, too.

[2000CAYukon]

Test to see if the pressure drops when you turn off the engine. Hard starting when warm can be a leaking fuel pressure regulator.

//2000CAYukon

[Adventurer_96]

Originally Posted by 2000CAYukon

Test to see if the pressure drops when you turn off the engine. Hard starting when warm can be a leaking fuel pressure regulator.

//2000CAYukon

Will do, thanks.

I hope I don't have to swap THAT out...

[Adventurer_96]

I was able to test the fuel pressure today. Turn it on and it's between 50-60. Turn it off, and it drops. Turn the key back on and it's back up, but on follow-up starts the fuel pressure drops slowly.

Leaking fuel pressure regulator?

[Adventurer_96]

Originally Posted by Adventurer_96

I was able to test the fuel pressure today. Turn it on and it's between 50-60. Turn it off, and it drops. Turn the key back on and it's back up, but on follow-up starts the fuel pressure drops slowly.

Leaking fuel pressure regulator?

BTW, how hard to swap out?

[2000CAYukon]

How far does it drop? When this happened to one of my neighbors, it would drop to 0 and it was real hard to start warm. Would even back fire sometimes since too much fuel was in the intake.

The regulator is under the Plastic Intake cover. Not sure how long to replace. Just know that it is a pretty common issue on the Vortec engines.

//2000CAYukon

[Adventurer_96]

Thanks, I just read an online how-to that talked about taking off the "upper intake manifold" and I was concerned this was going to be one of those huge jobs.

I'll check the Haynes manual a little closer tonight and I'll try to swap it out.

I didn't let it drop much below 30, at the rate it was dropping my guess is it was probably going to keep going below that though.

I hope it's not an injector.

[Adventurer_96]

BTW, do you actually have to drain the coolant to get the upper intake manifold off? The Haynes manual says to do it, but I'd rather not for obvious reasons.

[j cAT]

Originally Posted by Adventurer_96

BTW, how hard to swap out?

the fuel pressure should drop about 5 psi over 15min....if it drops faster than this there is a leak ....lines,injectors ,fuel pump,fuel regulator diaphram,,


if fuel is not the problem the ECT is the most common componet to cause your starting issues..this will not throw a code ...

[j cAT]

Before I get under the hood and start testing the coil, is there anything else to check out? I know I should replace the sparkplug wires, too.[/quote]

rather than just replacing the plug wires make sure you check the wire resistance and make sure you.. on installing new wires check resistance ,,also use dielectric grease on the plug wire boots..


normally an ignition problem shows up at W.O.T.........

[Adventurer_96]

Originally Posted by j cAT

the fuel pressure should drop about 5 psi over 15min....if it drops faster than this there is a leak ....lines,injectors ,fuel pump,fuel regulator diaphram,,


if fuel is not the problem the ECT is the most common componet to cause your starting issues..this will not throw a code ...

It drops MUCH faster than that. I'm guessing it's dropping about 5 psi every second, thereabouts.

No fuel smell and no obvious fuel leaks in the engine. The only codes I was getting was an O2 sensor that went away when it was changed and a MAF sensor right after which went away after one appearance.

Before the new fuel pump, the truck would do the same thing which leads me towards the regulator or injectors. I got about 15-16 mpg on the highway driving to Phoenix, but mileage drops significantly in town with all the trips I've been taking. My guess is I'm losing a lot of gas (thanks to the regulator) into the cylinders every time I shut the key off, if I understand the system right.

I'm going to attack the job on Wednesday. While I'm at it, I think I'll go ahead and replace the water pump I put in last December that's already showing signs of being worse for wear. I'll post back.

[Adventurer_96]

Originally Posted by j cAT

Before I get under the hood and start testing the coil, is there anything else to check out? I know I should replace the sparkplug wires, too.

rather than just replacing the plug wires make sure you check the wire resistance and make sure you.. on installing new wires check resistance ,,also use dielectric grease on the plug wire boots..


normally an ignition problem shows up at W.O.T.........[/quote]

Checked the wires yesterday, they're good. What's W.O.T. mean?

[Adventurer_96]

I replaced the fuel pressure regulator today. Not a terrible job, but not a great one either. I also replaced the crappy remanufactured water pump that gave me trouble after only a few months just as insurance for the long, cold winter.

But, it didn't fix the problem. Fuel pressure still drops after the truck ignition is turned on. Initially, it climbs to 60-62 psi then it drops steadily after that. My mileage is terrible around town with multiple stops.

The most eye-opening thing I found is the injectors. The front four were pretty gross from a PCV valve that hadn't been changed in a while. Two of the eight had a broken clip, and one of them had both clips broken off. The one with one broken clip had one of the four tabs at the end of the injector broken off.

I'm going to have to take the intake off again to replace the injectors.

Any suggestions here as to whether I should replace the individual injectors or the whole "spider" assembly?

Thanks...

[maxwedge]

Replace the spider, Dorman products makes a nice unit that has some improvements, Napa or Carquest have them.

[j cAT]

Originally Posted by Adventurer_96

Checked the wires yesterday, they're good. What's W.O.T. mean?

Wide Open Throttle