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99 K1500 Misifre/stumble

cjauto

By cjauto
in Ask A GM Technician

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cjauto Enthusiast

cjauto

Posted
Posted

Recently purchased this truck from a friend w/ couple of problems. '99 K1500 Xcab SB 5.7L Auto. The truck has had in the last 6-8 months a fuel pump, plugs, wires, couple O2 sensors, vent solenoid for fuel evap, all the common stuff. Intermittantly I've been having some type of stumble/misfire problem. It happens cold or warm, no given time. When the problem is happening it will still idle fine. As soon as a touch the gas and at any rpm it will mis. It has seemed to happen mostly around a 1/4 tank or less. If the truck is shut off it may or may not reoccur. It has never tripped the SES light. The only code i've read has been 172 (rich bank 1). Plugs don't look bad. I've read other posts saying possible plugged cats, is that possible? Where should I look first? This is driving me crazy.

blue-ss-camaro Enthusiast

blue-ss-camaro

Posted
Posted

welcome to the misfire and I dont know how to fix it club. I have the same problem right now and If you look down a few post at 97 5.0 p0302 and p0300 codes post he is have the same problem I have been told and have tried a bunch of different things with no luck so far. I have been told intake gaskets injectors(which I replaced) egr valve , fuel pressure regulator, distributor, and thats about all i havent tried yet. So good luck and if you find the prblem please post it on here. and i will do the same .

luminaapv3 Enthusiast

luminaapv3

Posted
Posted

I'm in the stumble club too, Welcome :chevy: . Except mine stumbles all the time, kind of getting used to the rocking boat problem :cheers: .

Next time it does it unplug the egr valve vacuum hose connected to the egr valve and let me know if it still does it. I don't have an answer for you, but am real interested in the results.

blue-ss-camaro Enthusiast

blue-ss-camaro

Posted
Posted

well I blocked off my egr valve today and I think it cured the problem I have a check engine light of course but its from the egr being blocked and not reading anything. I took it off and the spring is real weak Is it suppose to be like that? anyway going to leave it blocked off for a few days and see it I can get it to do it.

luminaapv3 Enthusiast

luminaapv3

Posted
Posted

I'm not exactly sure about your truck, but on mine if I just unhook the vacuum line from the egr valve and just push it aside (make sure it's far enough away from the valve or it could still operate the valve, doesn't take much suction) it runs ok and doesn't light up the check engine light in the dash, not good for the environment or gas mileage, but it does stop the stumbling :cheers: , if you figure out the cure please share.

cjauto Enthusiast

cjauto

Posted
  • Author
Posted

well, i'm glad i'm not the only one with this problem. smoebody has to figure it out. I did learn something yesterday. I was miss informed of the tune-up. It still had fact orig plugs, wires, cap and rotor at 133k miles. I changed them, but the problem is still there. While changing the plugs I noticed that #2 and #3 were fouled (not wet but carbon). I thought this might be some of the prob but no luck. If its misfiring why doesn't it trip a code or light? It seems to present itself more when I get done to about 1/4 tank. Fuel related? I'm probably take a look at some more today. hopefully something will jump out at me. thanks for the egr info i'll try that too.

blue-ss-camaro Enthusiast

blue-ss-camaro

Posted
Posted
I'm not exactly sure about your truck, but on mine if I just unhook the vacuum line from the egr valve and just push it aside (make sure it's far enough away from the valve or it could still operate the valve, doesn't take much suction) it runs ok and doesn't light up the check engine light in the dash, not good for the environment or gas mileage, but it does stop the stumbling :devil: , if you figure out the cure please share.

 

My egr is operated electronically. so if you unplug your egr vacuum line and it cures it I am thinking that its egr related have you taken your egr off and see if it stuck either open or closed. or maybe the spring is weak and it just comes on to soon and gives to much air. which I think would cause a lean condition and make it misfire.

 

cjauto Posted Today, 09:17 AM

well, i'm glad i'm not the only one with this problem. smoebody has to figure it out. I did learn something yesterday. I was miss informed of the tune-up. It still had fact orig plugs, wires, cap and rotor at 133k miles. I changed them, but the problem is still there. While changing the plugs I noticed that #2 and #3 were fouled (not wet but carbon). I thought this might be some of the prob but no luck. If its misfiring why doesn't it trip a code or light? It seems to present itself more when I get done to about 1/4 tank. Fuel related? I'm probably take a look at some more today. hopefully something will jump out at me. thanks for the egr info i'll try that too.

 

My truck does the misfire thing and it will sometimes set a light and sometimes not. Try unpluging the egr valve and see if you can get it to stumble. Let us know what you find out.

ZZ327 Senior Enthusiast

ZZ327

Posted
Posted

I had the exact same problem on my old 88 silverado awhile back and eventually replaced the EGR valve. The spring was stuck. Id bet money that is the problems for most of you

luminaapv3 Enthusiast

luminaapv3

Posted
Posted

Well I've replaced a ton of stuff, you can look at my post on this page called "Still Stumbling" with a green smiley icon.

The one thing that puzzles me is that I noticed that the egr solenoid will activate at about 1500 -2000 RPM's for just a few seconds when you hit the gas a little fast. If I slowly rev it up it won't do it, and if I rev it really fast you will feel a small slight stumble as it passes the above mentioned RPM zone.

I found this out by unplugging the vacuum line at the egr, put my finger over the end and reved the engine from within the engine bay (better to have someone rev it for you!) Sure enough as I hit this RPM zone the line had suction. Below the zone, no suction. Above the zone, no suction.

Has anyone changed any of these parts and still had the same problem after; ignition control module inside the distributor, Electronic spark control module, fuel injectors, fuel injector pressure regulator, oil pressure switch, ignition coil, fuel pump, IAC (idle air control switch) or the catalytic converter?????? Just wondering, so I don't have to waste anymore money. Just trying to narrow this down to save us all some time and money, not to mention our sanity or what's left of it :devil:

blue-ss-camaro Enthusiast

blue-ss-camaro

Posted
Posted
Well I've replaced a ton of stuff, you can look at my post on this page called "Still Stumbling" with a green smiley icon.

The one thing that puzzles me is that I noticed that the egr solenoid will activate at about 1500 -2000 RPM's for just a few seconds when you hit the gas a little fast. If I slowly rev it up it won't do it, and if I rev it really fast you will feel a small slight stumble as it passes the above mentioned RPM zone.

I found this out by unplugging the vacuum line at the egr, put my finger over the end and reved the engine from within the engine bay (better to have someone rev it for you!) Sure enough as I hit this RPM zone the line had suction. Below the zone, no suction. Above the zone, no suction.

Has anyone changed any of these parts and still had the same problem after; ignition control module inside the distributor, Electronic spark control module, fuel injectors, fuel injector pressure regulator, oil pressure switch, ignition coil, fuel pump, IAC (idle air control switch) or the catalytic converter?????? Just wondering, so I don't have to waste anymore money. Just trying to narrow this down to save us all some time and money, not to mention our sanity or what's left of it :devil:

 

well I have brand new catalyic converters on the truck and I replaced the fuel injector and just before i got the truck supposeally the guy replaced the fuel pump. so that elimanates those things. I am still driving my truck with the egr unplugged and I havent had it do it yet....

luminaapv3 Enthusiast

luminaapv3

Posted
Posted

I'm moving in the direction that this is some kind of electrical problem, maybe the ecm, or something not being grounded right or a bad switch that I haven't changed yet, like the expensive ones!

I say electrical because my egr system is brand new, the connections have been cleaned, but yet it something is still telling the egr solenoid to open up around 1000-2000 RPM's.

I'm leaning towards the ecm, because this controls the egr solenoid on my truck, but also it could be something else reporting back to the ecm that the engine is at a certain temperature or speed, then the ecm opens the egr.

Anyone change the transmission temperature switch, maybe that is telling the ecm that it is going faster than it really is?

Not sure if this is the real problem, but it sounds possible in theory :devil: .

If anyone has changed any of these items I just listed or the ones above please list it so we can eliminate that part as a source of the problem.

cjauto Enthusiast

cjauto

Posted
  • Author
Posted

Noticed over the last couple of days that this problem never seems to happen in the morning on my way to work(only a couple miles though). It seems to happen more often when the motor gets to temp. It only runs around 165 so I'm guessing someone has changed the thermo. Probably when they added the trans cooler. I've been thinking about buying a programmer to make it easier to retreive codes. I've been going to a friends repair shop. Can anyone recommend which seems to be best? Also, how would changing the software effect this stumble problem?

fourwheelinfool Enthusiast

fourwheelinfool

Posted
Posted

A year ago I had my truck in for some work and asked them to take a look at a similiar problem to what you guys are descibing. When I started my truck in the morning it would sometimes idle rough, with or without the check engine light on. One time I was able to get it to Auto-Zone to read the OBD code. Multiple misfire. It would go away after it warmed up and restarted.

 

Anyway, while the truck was in (at the dealer) for other work I had them check this as well. They ran a diagnostic and swapped the plugs around. The problem followed the plugs (thank god, as else I was looking at computer problems). They asked me if I wanted them to replace the plugs, I said no, figured I'd do it myself. When I got the truck back the problem had gone away and hasn't returned.

 

This happened at roughly 40k and my truck now has 78k on it, so whatever they did worked. I didn't pay for new plugs, so to my knowledge they are still original or only a few were replaced. If I remember correctly I had two misfires (two seperate cylinders).

 

:devil:

cjauto Enthusiast

cjauto

Posted
  • Author
Posted

mine had the plug change 6-8 months ago. I just changed them again the other day cause I saw #2&3 were fouled but not bad. its NOT tripping any misfire codes, which is weird. I can't be sure but my prob almost seems electrical sensor or something. thanks for the input though

 

 

 

A year ago I had my truck in for some work and asked them to take a look at a similiar problem to what you guys are descibing. When I started my truck in the morning it would sometimes idle rough, with or without the check engine light on. One time I was able to get it to Auto-Zone to read the OBD code. Multiple misfire. It would go away after it warmed up and restarted.

 

Anyway, while the truck was in (at the dealer) for other work I had them check this as well. They ran a diagnostic and swapped the plugs around. The problem followed the plugs (thank god, as else I was looking at computer problems). They asked me if I wanted them to replace the plugs, I said no, figured I'd do it myself. When I got the truck back the problem had gone away and hasn't returned.

 

This happened at roughly 40k and my truck now has 78k on it, so whatever they did worked. I didn't pay for new plugs, so to my knowledge they are still original or only a few were replaced. If I remember correctly I had two misfires (two seperate cylinders).

 

:devil:

luminaapv3 Enthusiast

luminaapv3

Posted
Posted

did full tune up recently, gapped the plugs myself, sure wish that was my problem.

My stumble issue actually starts a few minutes after the truck is started, i would say about 5-10 minutes later, after the truck warms up a little, doesn't do it if it is cold.

Might change out the ignition control module in the distributor, not too expensive and I know no way of testing this thing, but i do know that if these things overheat they will destroy themselves and when I cleaned up the distributor i noticed that there was no silicone grease under the unit like there would have been when it was new and a piece of the connetor plastic was a little broke too.

Hell i've changed just about everything else mind as well spend some more money i don't have on a part that won't change anything :devil:

 

I'll post back with the results. Wish me luck :bs:

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