chasing a wild rabbit

[jp115x]

Hey guys, I'm new to the forum and am in desperate need of help. In the past two weeks my truck has been low on power, my fuel economy sucks, and it feels like its hesitating or misfiring. I've already replaced spark plugs, my cap and rotor, coil, and coolant temperature sensor and nothing has fixed this misfire/hesitation. When I took the plugs out a few of them had a white/grey build up that I've never seen before and I figured that had to be it but it wasn't. Do I need a distributor next? I also recently put in a new fuel pump and filter so that's not the problem. Help me out guys, if yall need anymore info just ask! Thanks!

[00Silverado4x4]

How are the plugs as far as gap? May be time for new plugs.

[jp115x]

I already did plugs, the gap is 35 and that's what i set them to

[00Silverado4x4]

Have you checked the MAF/MAP sensor (don't remember which one you may have)? It could be dirty or failing. Also have you checked the actual fuel pressure? You said you replaced the pump, but it may not be getting to the engine. I'm just throwing out ideas of what to check prior to you buying parts that may or may not fix your problem.

[j-ten-ner]

...When I took the plugs out a few of them had a white/grey build up that I've never seen before and I figured that had to be it but it wasn't...

 

A few things what comes to my mind regarding to the color of the plugs.

 

-ignition timing

-lean fuel mixture

-wrong spark plug heat range

-engine is running too hot (cooling system)

-vacuum leak in the intake manifold

 

so long

j-ten-ner

[primered92]

I had the same problem on my '92 4.3. Turned out there's a little rubber hose on the fuel pump and it was split, recirculating the gas in the tank. You said you put in a new pump, but I don't remember if that piece is on the pump or the line. I replaced a lot of ignition parts on too of the engine before I figured that out. Guy at o'reillys just gave me the piece of hose because it's only about 2".

[jp115x]

Alright so I may have had a break through. Everybody who has had this problem has had a different fix. none of the things I've replaced so far have fixed the problem., but today I brought the truck in on my lunch break and put it up on the lift to give it a once over (I drove it a lot this past weekend) I've had a rattle under the truck for about a month now and I was looking to see what that was too. I gave the CAT a few raps and by what I can hear the honeycomb inside is broken up and making a rattling noise. Maybe this is whats getting in the way and causing sh***y flow? I'm gonna take it out and empty it tonight. I'll let yall know if that fixes it. Thanks!

[patriot]

A collapsed cat would kill power. Good catch.

[jp115x]

damn.....last night i emptied the cat, welded it back up, and it still runs like crap. Should I just get a new distributor? The alldata system I use at work is saying that most of the time that's the problem.

[j-ten-ner]

I would highly recommend to check all vacuum hoses and/or connections.

 

so long

j-ten-ner

[jp115x]

I have, I've gone over them at least three times now.

[Duelin]

"misfire/hesitation"

 

Is it a misfire or a hesitation? Have you diagnosed which cylinder or cylinders that might not be firing? If so are you getting spark to those cylinders. One thing comes to mind with those 5.0s a lot of them had soft cams. And the lobes would wear to the point that there wasn't any lift left. Resulting in a misfire.

[jp115x]

I'm not worried about the cams the truck only has 110,000 on it. Next thing I'm gonna try is a MAP sensor.

[Duelin]

I have replaced cams in those 5.0 with less than 50k miles on the engine. Like I said the cams were soft the metal wasn't treated correctly in other word defective. What happens when you disconnect the map sensor? Also what are you chasing a misfire or a hesitation?

[jp115x]

how can i tell its the cam causing the issue? I've replaced common parts and nothing is fixing it. I just tested MAP sensor output and its putting out 1.4 when the expected voltage is 1.0-1.5.