[Jaercole]

Recently my 99 GMC Suburban K2500 7.4L 454 started skipping slightly but only at around 80 mph at 2500 rpms. Did a complete tune up last year so don’t think it’s plugs, wires or distributor related. Injectors maybe?

 

[RayVoy]

No codes?

If it's a mis-fire there should be codes

 

[Jaercole]

Forgot to mention. No codes.

 

[Jaercole]

Maybe this’ll help. Since I’ve had it she’ll start right up after sitting overnight. But if you try to start her after she’s been running already that day it takes 5 seconds about of cranking for her to start. And when she does a puff a blackish smoke comes out of the exhaust. She’ll run rough for just a couple seconds but then smooth out and be fine. Ideas?

 

[Jaercole]

Someone told me I might have leaky injectors. I don’t know what that means.

 

[silverado002]

Leaky injectors means....... The fuel injectors in your engine usually have a pintle valve inside them which if worn or not seating properly will allow fuel to leak into the cylinders after engine shut down.
You should check your fuel pressure leak down rate to see if the pressure drops too fast after the engine is shut off.
If the injectors are leaking while the engine is running at idle or low speed it may or may not set a code for an overly rich mixture.

 

[xPosTech]

The rough starts and black smoke when starting warm/hot says leaking injectors, or leaking fuel pressure regulator. Pull the vacuum line at the regulator and smell it. If it has fuel in the vacuum line the regulator is bad.

You can rent a fuel pressure test kit for free at an auto parts store. Test the pressure at key on engine off, while idling, at 2000 rpm and the pressure drop when turning the engine off. The last at 5 secs, 15 secs, 30 secs and 5 min after turning engine off.

The test kit should include instructions that you can follow.

Ted

 

[Jaercole]

Excellent instructions. Thank you Ted. I’ll get on it this week. I’m most likely going to have a local garage I use and trust do it for me though. I’ve just watched a couple vids on replacing the fuel pressure regulator and it looks like it’s very hard to get to.

 

[Jaercole]

Mechanic says #3 injector was leaking. Says fuel pressure regulator and pump were fine but since he had the upper intake off to replace the injector I told him to replace the pressure regulator also.

 

[Jaercole]

Just an update. Got the Burb back today and she’s running very smooth. Have yet to drive it highway speeds but I think the issue is resolved. Also I found another thread about this very same topic from 2014 on this site. It was very informative.