Time for a new Fuel Pump? Confused...

[Nichoms]

I've got a 1999 Yukon Denali, its got 170k on it but has been running great since I've owned it (about 8 months).

About 4 months ago I did the following:

Spark Plugs
Wires
Dist Cap and Rotor
Fuel filter
Water Pump
Intake manifold gaskets
-while I had the intake off I cleaned the spider assembly really well with carb cleaner
Various suspension components

It ran well for months after all that.

So yesterday I was driving around and it was doing great as normal. Stopped at a gas station and got a drink, then when I started it back up it was idling very rough. I looked under the hood and cyl #3 spark plug was moving a little, so I limped it home and tightened it up. No Change.

I hooked up HP Tuners and read the codes P0300 Random misfire.

Checked all the sensors and they were hooked up, wiggled the crank position wiring as I read the wiring is a little touchy. Checked for vacuum leaks.

All yielded nothing.

So I rented a fuel pressure gauge and got the following:

Key on: 62psi
Idle:52-55psi
Blip of the throttle: bounces to 60+psi
Driving in the neighborhood and floor it I will get close to 70psi

The engine idles a little rough, then real rough around 1500rpm but smooths out over 2000rpm. Stumbles off idle accelerating.

Showing to get some knock retard when I get on it.


Sorry for the long post but this isnt my daily so I'm not in a hurry, and dont want to just start throwing parts at it.

Is this the standard "fuel pump going out" issue? If so, why is it still spiking to 70psi when I get on the throttle?

Any suggestions?

All help is much appreciated

Nick

 

[PlazaEJ]

Try cleaning the MAF?
How about the air filter?

 

[Nichoms]

Air filter was also replaced 4 months ago.
I can try cleaning the MAF, I've got some MAF Cleaner. I just figured it would throw a MAF Code...

I will try that tonight though for sure.

 

[noJeepshere]

Those numbers are perfectly in line for a good pump, I see no problem there. I had a similar issue on mine a few years ago, and it ended up being the egr valve was sticking open. That allowed too much exhaust gas into the combustion chamber at low speed and would choke it until I either got deep in the throttle or higher revs.

 

[Nichoms]

Ahhh... thanks for the EGR idea. I could see a stuck EGR causing this issue.
Is there not a Code for bad EGR?

Is there a way to test the EGR? Hook up a mitivac to the port and see if it holds a vacuum on the diaphram?

How much trouble is it to replace?

Thanks

 

[noJeepshere]

Ahhh... thanks for the EGR idea. I could see a stuck EGR causing this issue.
Is there not a Code for bad EGR?

Is there a way to test the EGR? Hook up a mitivac to the port and see if it holds a vacuum on the diaphram?

How much trouble is it to replace?

Thanks

It's on the front of the engine near the water outlet. Two bolts and a plug. The bolts can be a bit annoying to get back in though. Easiest way to test it is to pull it out and shake it, if it's good, you'll hear a rattling, if it's bad, you won't. While it's out, soak it with some carb cleaner and get the carbon out of it.

 

[Nichoms]

Ok thanks for the help.

Here is my list of things to check when I get off work:

-Clean MAF
-Check for Coolant Loss
-Check long term fuel trim (greater than 7% could indicate a vacuum leak)
-Disconnect EGR
-Remove EGR and shake
-Clean EGR

If none of that does it I will keep on thinking/researching/testing things...

 

[SunlitComet]

egr have there own codes if it does not respond correctly to its requests from pcm. before the issues what mileage were you getting btw. And consider having a injector balance test done. it should be about $100 and will tell you right away if the injection spider is at fault just by chance. in the meantime, what parts brand and numbers did you use?

 

[Nichoms]

Yea, I'm wondering if it hasnt thrown an EGR code because I havent driven it much since the problem came up. I've driven it maybe 1 mile total since it started, and its been at about 10-35mph. It has idled for about an hour while I was diagnosing things.

I havent done extensive testing of the MPG since its just my 3rd vehicle that I take the dogs in and use pretty much as a truck to throw stuff in the back on the occasion. But I think the time I did test it I was getting 13-15mpg. Pretty much on par with my other friends with vortec 350s.

Can I do an injector balance test or will I have to take it in somewhere?

Spark plugs - AC Delco
Plug wires -middle of the road brand I cant remember
Intake gaskets - Felpro with the metal backing instead of the plastic
Fuel filter - Wix

 

[Nichoms]

I think I narrowed some things down yesterday. I tried everything I listed up top and got nothing. I data logged and my LT B2 is pretty high at like 21. Not exactly sure what that is telling me though.

I went through and disconnected the plug wires one by one and I ran across something odd. When I pulled the #2 plug wire the engine started running a little better, I would put it against the manifold and it wasnt jumping a spark. #4 and #6 were ok, then #8 was the same as #2. Then with #8 plug removed #2 would jump a spark. So I removed #8 wire and drove it in the neighborhood, it drove much better, lost the hesitation and felt like I had power again. So I threw another plug wire on #8 hoping that would help. It didnt.

So here is what I think may be happening: I think the distributor cap (Only 4 months old) is shorting out #2 and #8. I removed the cap and looked and it looked fine but I'm thinking maybe interally there was a crack or something and it is letting #2 and #8 contact or let the arc jump across. This is making the spark on #2 happen when #8 should be happening.

Does this seem possible or would it be the Ignition Control Module?

I dont want to start throwing parts at this as I'm still $0 in at this point. Is there a way to test the control module? My friend has a spare almost new distributor that I am going to get and try out.