Need help diagnosing a miss.

blacktransam

blacktransam

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Joined
Aug 24, 2010
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14
Alright, i've searched and searched to no avail.

My 98 12 valve 356k miles has developed miss that sounds like a popping at idle out the exhaust. It "seems" to smooth out when throttle is applied aka raising pressure. If I start the truck from dead cold and run a lazer thermometer on all 6 exhaust runners they are all between 135-150* except cyl 3 which is 185+. I had a set of 100 horse injectors in the garage I was going to install with later mods so I figured maybe the stockers had seen the end of there days and threw the new ones in. The problem persists except every cyl goes up 10* so obviously more fuel across the board and evenly.

Am I right to assume possibly a delivery valve or holder? I have this idea of swapping holder's 3-2 and DV's 3-1 and see if and where the increased temperature goes. If it stays at 3 I ASSume i'm looking at a pump issue. If it moves to 2 or 1 i've obviously found my culprit. Any other suggestions? Am I even on the right path? Can i visually look at DV's or holders for defects?

Also just some more info, theres very light "puffs" of smoke at idle, like i have one cyl fueling heavy.

I'm trying not to buy all new DV's and holders a few weeks before Christmas.

Thanks for the help guys.

Mike

BTW Yes i've been on this board for a while and never posted, I prefer to read and learn but i'm kind of at a loss here.
 
Oh also now when the truck goes into lock-up it shutters, Like that cyl is missing and its a dead hole, however if I bring in a little more throttle she's smooth as can be. Running down the road at 70, smooth as can be.

Just trying to give as much info as possible


I also had thought of timing, but I don't understand why it would lean on 1 cyl more than others.
 
Is there any noise out the intake? Pull your valve covers and check lash. That would help you determine if its a mechanical issue. Smoked cam/tappet, bent push rod, or I've seen the retainers crack out and the hole get bigger where the valve comes through. This happens right before you drop a valve.

Just some other ideas. That stuff is easy to check so I always check it first.
 
I set lash maybe 8 months ago, and I didn't think to check it again. I will check it tonight, thats free and easy.

Thanks
 
no smoke? white or otherwise? When I developed a miss, with heavy white smoke, my head gasket had let go.

the other thing I have done is take the injector lines off, key on, pull the fuel shut off sol. up, either button crank or have a friend crank it while holding a cardboard box for the fuel to spray against. They should, obviously, all spray fuel, and be more or less even. this could show a problem in the IP.

If one shoots low/dosent shoot either pull the DV and see if something obvious is wrong or pull the pump and find a shop to go through it.

Ive seen a few of pumps cause this problem, honestly not sure what causes it, Iknow its something in the DV, but when I serviced these pumps we puilled them and sent them to a local diesel shop to go through them.
 
If it's a valve you could check by disconnecting the shutdown solenoid harness then crank it with the intake horn removed. Listen for unusual sounds like air shooting back into the intake (also would be a lot of soot in there).

Then do the same thing for the exhaust, listen at the tailpipe while cranking. Works easier with two people ;)
 
All awesome idea's thanks guys, I didn't get a chance to touch her this week, but I will be after work today.

Thanks alot.
 
Totally forgot about this, i figured out the issue, it seams as though the previous owner attempted to "turn the barrels" and didn't get all the nuts tightened back down, had some barrels turned, some not. All smooth as silk now.
 
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