Engine/Transmission (1994 - 1998) Engine Lope

[BTanzini]

Need Help with diagnose's,when my engine is cold it runs nice and smothe but when it heats up it starts loping alittle. I have been using Standydine fuel additive since 24,000 miles at every fill up. I suspect an injector but not sure, would overflow valve cause this or what else? Thanks in advance.

 

[Blackcloud]

Sounds to me like your idle is set to low. DC says around 750 rpm with truck in gear.

 

[bmoeller]

Originally posted by Blackcloud

Sounds to me like your idle is set to low. DC says around 750 rpm with truck in gear.

And with A/C on.

 

[BTanzini]

Just got through increasing idle with a/c on, in drive and lites on. Lope was there before idle increase and is still there?????? Thanks for input. Idle is about 800 rpm.

 

[JGK]

Is your lope only at idle or all through the rev range? If all through the rev range, it sounds like what I experienced. Tell me more about its characteristics.



-Jay

 

[BTanzini]

Jay; lope seems to stay until 1400-1500 rpm then smooths out to unnoticeable. Thanks.

 

[JGK]

BTanziniSr,



Tell me more. Does it go away at 1500 revs or due to the frequency seem to fad into the background, but is still there? Would you characterize it sorta like a miss (weak injector, for instance) or does it remind you of an exhaust leak on 1 cylinder (that noticable pop you hear)?



These were the characteristics of mine. It would be a little worse on some days, then not so bad on others. I'd notice it until at least 2200 rpms or so, however, then it would smooth out a little. Truck ran fine otherwise. An infrared remote thermo gun showed #3 running 75 to 100 degrees cooler than its neighbors at the exhaust outlet on the head.



The weird thing is, it seems to have cleared itself up!



Not sure I have any answers, actually, just trying to find if someone else has had a similar proplem and what they've learned.



Thanks,

-Jay

 

[BTanzini]

Jay; to me it feels alittle like a miss on a gas engine, not a bad one but enough to notice at idle, it seems to disappear at about 1400-1500 rpm, I do not here a pop of any kind and it does not feel like it affects performance of any kind. Thanks Bill

 

[JGK]

Bill,



My attempts to figure out mine included the following:



Checked exhaust manifold bolts, found 2 or 3 loose. Tightened them, but it didn't help. I eventually replaced teh manifold for an ATS 3-pc. Didn't help.



Check valve lash. Didn't help.



Replaced check valve. Didn't help.



Replaced lift pump. Didn't help.



Swapped delivery valves with adjacent cylinder. Didn't help. Temp on #3 didn't change.



Swapped injector with another cyl. Didn't help. Temp didn't change on #3.



Had injection pump checked and bench tuned. Didn't help.



Did compression check. All cylinders read roughly the same.



Replaced fuel filter, checked everything I could think of, etc. Didn't help. I finally decided to just live with it until something happened. As I said, it eventually cleared itself up. The only mods I did during this time is add the PDR HX40 turbo and change over to a #10 plate (more power!).



My only other theory was that perhaps the exhaust valve on #3 was not closing completely due to something on the valve seat, or ??. But the compression check I would think would have shown that. The only other test I didn't do but might have indicated this is a leak down test.



In any case, if that was it, or something like it, it appears to have fixed itself. One of these days I'll have to check the temps again with the infrared gun.



You may end up just having to wait it out like I did.



-Jay

 

[HoleshotHolset]

Did you ever try to do an Italian Tune-Up on it?



(Take it out and beat the snot out of it?)



The gasser musclecars of years past were famous for tremendously inefficient A/F ratios that would make them load up and get carbon buildup. A quick jaunt on the freeway was usually enough to dislodge most of the carbon..... a periodic slow pour of a Coke bottle full of water down the carb would also help to steam-clean the carbon out... . Whatever you do - never do the Coke bottle trick on a diesel - unless you like doing damage.



Matt

 

[JGK]

Did you ever try to do an Italian Tune-Up on it?

HoleshotHolset,



That's sorta what I did by swapping my #11 plate for a 10 moved forward, putting on a PDR HX40, then getting on the throttle a lot and blowing a lot of smoke. I figured I either make it bad enough to find it, or it would fix it. So far, it seems the latter.



-Jay

 

[Lightman]

I Had The same problem on my 94 it turned out to be low fuel pressure at idle I had 18-20 at idle and the lope, shimmed my over flow valve up to 26-28 psi at idle lope is gone.

 

[BTanzini]

Lightman, JGK.



Thanks for your reply I will be towing next week so I will push it a little and see if that helps, if not I will check the overflow valve and if that is not it I will connect my FP gage and check fuel pressure to. Thanks again. Bill T.