Engine/Transmission (1994 - 1998) 95 missing at high RPM and grey smoke

[LSMITH]

Guys, I have a favor to ask. I would like some help with a problem dad is having on his truck.



Dad has a 95 12V with an auto. #6 TST plate full forward and is having some trouble. For a long time (maybe since he got it with 50K on it) over about 2300 RPM it would start smoking grey and missing/running rough, not terrible rough like it is going to blow up but you denfinately notice it. Grey smoke is pretty heavy. We both thought it was the governor pulling the fuel back, but weren't really sure or all that concerned. The TST plate install did not make it any worse or any better.



He just put in a set of 3K rpm PDR governor springs this weekend, looking for a little easier time towing his 5'er in the mountains. Now it will make about 2500 before it starts rinning rough and smoking grey, but held to the floor it will only reach about 2600 and EGT sits right at 1400, boost at 26 psi or so. It would hit 1400 at 2300 RPM before the spring install, 1400 is pretty normal max for this truck with the plate where it is as is 26 psi empty. Fuel is clean, filter is new, valves are adjusted. Lift pump pressure is unknown, but a guess is that it is getting plenty as EGT stays up. Timing is stock as far as we know. Injectors are stock. The spring install is not really a suspect either as the problem was there before, and has not changed except for moving up 200 rpm or so. Spring height is the same as stock, install was according to PDR instructions.



Any ideas on where to start looking for the problem? Thanks for your help.

 

[J.R. Adkins]

Check the FP.

 

[T. Baker]

I'm wondering if the timing slipped. The other thing could air be getting into the fuel somehow? That would make it run rough. The higher rpm could cause more vaccum in the pickup line causing air to enter the fuel.

 

[Stixx]

My 94' would do the same thing, the fuel heater was sucking air. I just bypassed it and I see no reason for the heater anyway.

 

[Deezul1]

One thing thats easy to check is the overflow valve. If it is the take apart kind (some of the early one wernt) pull the spring and make sure it is at least . 500 long. If its not then stretch it to . 550 and see what happens. It only takes abou 15 min to do it. On mine I couldnt get the truck over about 60mph towing a 6000lb trailer without being flat on the floor. That was my 1st truck and didnt have gauges then so dont know about EGTs but it felt like there was no boost.

 

[Dennis Garrett]

If the engine is good and hot, put in in nuetral or park, and floor it. It should run right up to the redline, run smooth, with a light haze at the exhaust. If the timing is off, it won't run smooth at all, and you'll get a lot of smoke. Might also check the lever adjustment, I had to adjust mine after I put in the GSK.

http://www.piersdiesel.com/LeverAdj.htm

 

[J.R. Adkins]

A truck with stock timing wont pull to redline. They will stumble @ about 2200. But every truck is different.

 

[Ben Rumson]

Timming

I'm guessing it's your timming. Stock timming doing the supplyiing with modified demand - not advanced enough for the higher rmps, fuel needed, etc.



Mine stumbled slightly under similar conditions - and the advanced timming cleared it up.

 

[Stixx]

My 13. 5 timing doesnt stumble.

Never did.



hmmm



Maybe its advanced more then they said.

 

[LarryB]

I agree with the above. Check fuel pressure and timing. Also, what condition is the cat converter in? Let us know what you find.

 

[BigYellowIron]

TIMMING!



You will probably notice a sound kinda like a a slight backfire comming out of the exaust when you floor it in neutral.



Adam

 

[LSMITH]

Thanks for the feedback guys. I am on the road this week so my ability to check and respond is not good, but dad is looking in and will check what has been pointed out. Thanks again, we appreciate it.

 

[bbeatty]

grey smoke at high RPMs

LSMITH: There are only two thigs it can be,Late timing or an excessive air leak. (got a intake air leak and it opens enough at high boost,could be a hose, but would Iwould suspect you would here it. I dont think there is any thing else to look at. thanks for your time BBEATTY

 

[LSMITH]

Thanks for all of the advise!!



Timing is going to be adjusted to 15. 5*. A new overflow valve is also going in, and we will see where that leaves things. Again thanks for all the help.

 

[LarryB]

Don't forget to let us know. We're curious now.

 

[Deezul1]

Hopefully the 2 repair items can be done seperately so we can find out which it was.

Good Luck

 

[LSMITH]

Update

Timing was set to 15. 5 per Piers. It helped some. He can get 2700 out of it now before it starts getting rough, so he pulled the overflow and tested it. It is bypassing at 8 PSI, so it is going to get replaced. Cheapest he can find one is $55, are they that expensive? Never bought one but I was guessing $25 tops. Any help on the overflow valve would be appreciated, and I will update on how it runs when it gets replaced.

 

[M Barnett]

I think the price sounds about right.

Michael

 

[Deezul1]

Thats a real decent price, I have not seen them any cheaper. Stretch the spring to . 550 and reinstall it and see if the problem is solved before buying a new valve but at 8 lbs it needs a new one anyway.

 

[Ben Rumson]

I paid $65

... for a new one a few years back. You're price is good. I concur Deezul 1, stretch the spring and see if this helps - if it does, run it till it flattens out again and restretch it, or replace it.



Good way to know if this will clean things up or if you'll have to keep tinkering after spring replacement.