Rough idle and buck @ 2200rpm with blue smoke

[carhauler]

This is on a 1994 12 v 5speed I dle seems very rough and it feels like the truck is losing a cylinder @ 2200 and bellows blue smoke only mod is a tst 250 plate .

Is it losing an injecter ?



Ps 175k on engine,, plate has been in for 2 months and this happened before the plate was installed.



Thanks jim

 

[Power Wagon]

Originally posted by carhauler

This is on a 1994 12 v 5speed I dle seems very rough and it feels like the truck is losing a cylinder @ 2200 and bellows blue smoke only mod is a tst 250 plate .

Is it losing an injecter ?



Ps 175k on engine,, plate has been in for 2 months and this happened before the plate was installed.



Thanks jim

I can't speak to the injector health, as you never said if they've been replaced or not... But, absent a serious injector problem, this is symptomatic of either a bad overflow valve or timing being too far retarded.



The 94's were all too far retarded anyway, with the stock specs being such that it wasn't uncommon for trucks to not want to run smooth until fully warm, even if carefully timed. Instead of it's 11. 5 to 12. 5 timing range, it should be moved up to around 14, which will make great improvements to it's responsiveness, cold running, and economy, with less smoke.



A bad overflow valve often results in missing, popping, smoke, and/or just flat-out dropping cylinders with no smoke at any speed from idle to WOT. Sometimes it has no symptoms other than a trail of blue smoke when going downhill.

 

[carhauler]

The injectors are stock ,When it is cold it feels like it drops 2-3 cylinders and smokes like a freight train. Where is the overflow valve and how can you test it?

 

[Power Wagon]

The overflow valve is basically an overgrown banjo bolt with a spring and check ball in the outlet. It holds the return fuel pipe to the pump, which is the pipe that runs down between the engine and pump and connects to the pump next to the gear case sort of behind the oil filler. There is a notch in the head which should allow you to be able to remove it. It should JUST fit between the head and pump housing.



Testing involves checking your supply pressures while running, as it's purpose is to hold fuel backpressure against the supply pump, thereby pressurizing the fuel galley in the pump. You can tap the outlet of the fuel filter, where there's a little pressure tap already in place (small bolt on top of the banjo bolt that holds the supply pipe in place that runs between the filterbase and the "back" of the pump - about a 12 -16 inch long pipe). Or, you can go to a pump shop and they have the stuff to check it agains their calibrated gauges... test it under a variety of flows.



Memory fails, but I think used is a minimum of 1. 5 Atmospheres (1 Atm = 14. 7 psi), and newer, revised regulators are about 2. Higher is better, low is bad. Someone with better recall than me may be able to verify or correct these figures.



I do know that if it's less than 15 PSI, forget it. YOu need a new one for sure.



But don't forget, a coiuple bad injectors could conceivably do the same. I would guess their expected life to be roughly 150 to 200K miles.

 

[Extreme1]

A 94 would have a sealed valve. It looks like a ball bearing is pressed into it.

 

[Cooker]

Sounds more like timing IMO, especially if it is really bad on a cold start.



JMHO,

Ryan

 

[Evan A. Beck]

Check the fuel pressure first, and if that checks out ok (16-20 psi @ idle), have the timing checked. I've had about 6 trucks in since late October complaining of the same problem you are having. Poor running and blue smoke on a cold start is 9 times out of 10 dues to retarded timing.