Engine/Transmission (1994 - 1998) where is the boost goin??

[Diesel Fever]

Hey guys. I searched every way possible on here but could not find the part number for the gasket(s) for where the air horn meets the engine intake. I've had a boost leak for quite sometime now. I replaced all the boots and clamps with bd diesel's boot kit from genos. I blocked the wastegate by pluggin the top of the t on the afc housing, but still only hittin 7-9 psi. I don't really have a way to pressurize the system to check the intercooler. So the only other thing I can think of is that gasket or gaskets. I also read that low fuel could not allow the turbo to reach max boost, but it sounds like it is. I do have an air leak, cranks like a powerchoke, so maybe bad lift pump aswell? Any suggestions would be very helpful, can't live without boost :-laf. Sorry for the lenghthy thread too :-laf. Thanks in advance, take care.

 

[fest3er]

Well, yes. If you don't have enough fuel gettin' to the engine, it won't make enough hot exhaust to spin the turbo ever faster. Remember, boost and fueling is a chicken/egg problem: you gotta have more boost so you can use more fuel, but you gotta use more fuel so you can make more boost.

When did you last change your fuel filter? Asphaltenes clogged my filter in 14K miles to where my elderly lift pump couldn't get enough fuel to the engine; I was limited to about 9-10 PSI boost, except for a momentary jump to 18 while there was enough fuel past the filter. The engine ran great, though I knew it was feelin' a mite poorly.

So if you ain't changed yer filter in a while, you should do so. And check the pre-screener while yer in there; it's prolly clean, but if you ain't checked it in a 100K miles, you should.

 

[kenny61]

Diaghphram in the AFC have been know to tear as well. this will keep it from fueling

 

[GOlsen]

I think this is the gasket you were looking for:

94-98 12 Valve Dodge Cummins Small Heater Grid Gasket

 

[hsmith]

Get an intake set from NAPA and it includes that one. Cheap.

 

[Diesel Fever]

GOlsen, thanks that's actually what I found later that night and ordered. I appreciate all the inputs guys, I also forgot to mention that my egts never get higher than 600 degrees, pre-turbo pyro. Idle will be between 250-300. I never have a load, just the truck itself. Doing the searches I've read that most guys who have a pre-turbo pyro have double the temps that I get. Not sure if they had a load or not, but I think my egts are below the average temps. Could this also be a fueling problem? And as a result, low boost? Thanks in advance, take care.

 

[Joe G.]

If the hose to the AFC is broken, cracked, or disconnected it will act like that. You have to have boost to the AFC or it won't work.

 

[Diesel Fever]

Well, there was no difference when I disconnected the wastegate hose. Same results with or without. I did not check to see if hose was cracked or anything so that is still possible. I wasn't able to check the afc today either since today was a complete wash out, so dunno if the diaphragm is bad yet either.

 

[Joe G.]

You can test it by taking the AFC off. Cover up the hole to keep oil from flying out of it and go for a test drive. If the AFC was the problem it will go pretty good and smoke like a forest fire.

 

[Diesel Fever]

Ok, thanks for the advice. Hopefully this weather clears up around here and maybe I can give it a shot tomorrow. Thanks again for all the help, take care.

 

[KYOUNG]

check your fuel pressure!

 

[Diesel Fever]

Fuel pressure is about 20 or so when cold, 24 when idling fully warmed up, and 30+ when driving. I have yet to find where the air leak is, but she takes quite a few cranks to start, even when already been driven, shut it off, and start it back up, will take 5-6 cranks. I think the lift pump might be the problem, low power and lost prime but I'm not 100% sure, maybe a tear somewhere. Gonna test and see if the afc is also bad soon aswell, just gotta find a way to block the hole first. Has anyone ever found an air leak on their truck? If so where abouts was it? Hard to find new line and replace? Thanks in advance, just thumbin through the maybe's. Take care.

 

[fest3er]

Hard starting simply means that no fuel is getting to the engine for a while. The most basic reason for this is that fuel is draining back to the tank. This could be due to a faulty overflow valve on the p-pump, cracked fuel line(s), stuck check valves in the lift pump or several other reasons.

Low boost means limited fueling, which can be caused by any number of things.

Your fuel pressure seems OK. For where you measured it. Measure it at the p-pump, if possible. A difference will point to something between the two measurement points.

If fuel pressure is OK at the pump, the next place to look would be at the torque plate and the AFC. Apply, say, 10 PSI to the AFC from a small static source; if the pressure remains steady (or nearly so), the AFC should be OK. If you can, apply regulated 20PSI to the AFC and drive the truck; if it behaves differently, you may not be getting boost from the intake manifold to the AFC.

 

[Joe G.]

You can use a piece of duct tape to block the hole. If you are trying to start it without using the fuel pedal your low idle may be the cause of hard starting. These relics DON'T have a computer to start them like every other vehicle on the road. Having to use a little pedal is OK.