Random issue, bad mpgs, hesitation

ChevroletTough · February 10, 2020

Hey guys. Thanks again for all the input as I work this 2000 (7.4L) k3500 back to good shape. It has been making me money plowing, quite a bit this year. I have the front rotors/hubs/wheel studs all ready to go, just need to get the job done.

Seems I have a random issue showing up now. Truck will seem doggy, horrid MPGs, can almost feel it missing damn near but will idle fine. When I get it going it will hesitate a bit up until cruising speeds. This is intermitent. Yesterday it ran flawless and had great mpgs. No flashing CEL lights, so it can't be an actual missfire. Gotta believe the ignition is good. So I'm really thinking fuel.

I have not yet hooked up my live monitoring when it does this. But plan to do so. Was thinking intake manifold, but if that was the issue I'd have it all the time (right??). I do have a code for an 02 sensor but that's because I believe I have 2 that are deleted. Truck has a new ECU as well FYI.

I'm wondering if this is fuel related though. Possibly the fuel pressure regulator going bad. I have no way of proving this at this point, but it's on my radar.

Have also checked into the MAP sensor, but if that was bad, I'd have a code.

This "issue" will come and go. Sometimes it runs great, and randomly it will do this. Normally I can shut the truck off and restart it and most of the time it goes away, but not always. It was really apparent when I was pulling my enclosed trailer this weekend with 2 4 wheelers. No engine temp issues. Transmission shifting great. RPMS seem to build ok, but it will hold them a little longer.

No codes yet.

Edited February 10, 2020 by ChevroletTough

ChevroletTough · February 12, 2020

after further research it may appears the injectors are acting up. I found a good replacement that people are swearing by. The replacement job is somewhat involved. But not awful. Since the intake plenum has to come off, I may look to do the FPR anyway.

Looks like a weekend jobby but not too bad.

https://www.summitracing.com/parts/URM-6016

ChevroletTough · February 19, 2020

Put a lot of fuel injector cleaner in and ran it lower of fuel than I normally do.

Appears the only time it does this is when I’m pulling the enclosed. Haven’t had it happen again while plowing.

I’ve done a lot of reading and people have resolved this with many different things... some really weird:

Coolant sensor
Injectors
Fuel pressure regulaor
Maf sensor

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thx1138v2 · February 22, 2020

One other thing to check. I looked for a couple of months for this one and it was driving me crazy. Same symptoms but on a '94 C1500 4.3L.

My exhaust has catalytic a converter. Inside that converter there is a canister that holds the chemical pellets. That canister had come loose and it would occasionally get turned sideways in the pipe blocking about 85-90% of the exhaust gas flow. I looked at everything I could think of under the hood. I decided to change the catalytic converter at one point and once I had it off I could see what was going on since it was one of those times when it was running poorly. Just to verify my guess I knocked the canister out using a 3' X 1/2" steel rod and bolted it back up. Ran like a champ.

You can check it by holding your palm against the cold exhaust tail pipe one of those times when it is running poorly. Feel the pressure. If it feels full pressure that's not the problem. If it feels weak that may be your problem.

ChevroletTough · February 22, 2020

Will do but I have no cats [emoji1787][emoji23][emoji1787][emoji23]

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ChevroletTough · February 24, 2020

So, it did it again. On the trip down pulling the enclosed, no issues. On the way back up, did it right away.

I turned the truck off and turned it back on, it seemed to improve, but was still doggy, had poor fuel economy (not what I would expect).

The only thing in common thus far is I fueled up at the same place on the way up and down. I really don't think that is my issue here. I'm really leaning towards injectors after my research. I have 0 codes for missfires or fuel pressure. Truck studders and falls on its face a bit but will always go when the pedal is pushed. It sure sounds like a miss though to me when it's doing it.

This issue is not noticeable when the trailer is unhooked. It sure seems like a "need power" demand situation. I may have the shop hook up a fuel pressure test to it and see.

If I do go this route, I would replace the intake manifold gasket, rotor, cap, wires, plug wires, injectors (with known reputable style from summit), and the fuel pressure regulator. I believe I can tackle that job myself on a weekend.

I am going to use the seafoam intake spray tonight and clean that up. It's pretty black behind the throttlebody (which I have already cleaned). That seafoam stuff is supposed to do wonder for the intake. I wish this truck didn't have an EGR valve, those things just gum up intakes.

riverbanks · February 24, 2020

So,demand for power issue,if tune up stuff is old,I'd go there,wires,cap and rotor,you could spray water on wires,a light mist,see if you can introduce the skip at idle with hood open,then lower hood,peek in,see if you see arcing

ChevroletTough · February 24, 2020

10-4 will take a look. I bought this truck about 6 months ago, no clue on plugs and wires, wires don't look old. no clue on cap/rotor either.

I have been doing a lot of reading on this. I may try the MAP sensor. Seems as though that is a common "no ses light" but will cause all sorts of problems. I know where that sensor is, but man it looks like it'll be fun to replace.

I may also take the EGR valve off and check it.

riverbanks · February 24, 2020

Map is just reading vac,but important sensor,they usually go bad,not flaky,as far as the spider injection,pull plugs and checking for even color,same,it's good,uneven,worn poppets

ChevroletTough · February 24, 2020

10-4 will do.

Sensor is in a tight spot but it just pushes in, so should be easy to replace. Ground from it, looks good.

I am going to also replace the coolant sensor (waterneck) as that appears to also be a potential problem. I have new upper and lower rad hoses, just replaced the bypass hose as it was leaking a TINY bit. I also have a new water pump as I thought that was what was leaking, but it isn't. I think I'll probably return the water pump.

ChevroletTough · February 25, 2020

Coolant sensor didn't change a thing, but my coolant is now new and not gross. New hoses too.

I plan to seafoam the upper intake tonight with my son's help.

I should probably work to get the o2 sensor replaced, I have a CEL for it.

What I have noticed: if I rev it in park or neutral, there is a bit of a stumble if I hold it at 1500rpms. Anything higher or lower seems to be good.

I am probably looking at doing the injectors, fuel pressure regulator, cap, rotor, plugs, and wires this summer. Going to be a alot of $$$ for me doing it myself even. Oh well.

Somtimes it starts up instantly, others it cranks for awhile and comes to life. Sure feels fuel related to me. Leaky injector(s) could be the problem I have a lot of black crap in my tailpipe.

MAP sensor comes tomorrow, maybe I'll get lucky.

I might have the local shop look at it and see if they can tell me anything.

ChevroletTough · February 26, 2020

I only got about 1/3 of the can of seafoam out. Faulty.... got my money back, will make another attempt.

Going to check the fuel pump terminals. Fuel pump relay is pretty cheap might just try it for S's and G's. Fuel filter would probably be a good thing to do in general.

I'm really betting this is the injectors though.

ChevroletTough · February 27, 2020

So, one can't just simply swap out the map sensor. There's a metal tab bolted down ontop of it to hold it in place... which is mostly hidden by the intake manifold/plenum. So I'm going to try to get really tricky with a universal joint. If I can't. I'll have to wait until I tackle the intake manifold/plenum job this summer. Son of a diddly.

ChevroletTough · February 27, 2020

After another look, if I remove the water neck I can get to it.

Water pump is now going so I have will have to drain the coolant again anyway. I had a bad feeling getting fresh fluid in would kill the water pump. Oh well, I can replace the map sensor now too i guess....

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ChevroletTough · March 4, 2020

So, after having the shop replace my brakes and wheel bearings... I had them look into this issue a little.

B1S1 oxygen sensor is bad, will replace.

fuel filter should be replaced

Fuel pressure regulator is bad.

I am going to work on taking care of all of these and see what happens. I am well aware I need to take the upper plenum off to get to the fuel pressure regulator.