Low boost on a 94.......
 

I usually don't work on the "dark ages" trucks but a good customer wanted me to look over his 94. It starts and runs fine, but he seemed to think it didn't have the "grunt" it used to. Also said the turbo didn't sound right. I drove the truck and it ran fine, no smoke, but definately didn't have much pull. I checked the fuel which looked fine. It has a good filter on it. I checked the air inlet system and pressurized it. Air charge system is tight (no leaky boots), but I did find that the actuator for the wastegate is leaking so theoretically it should overboost if all is working correct. I thought of fuel supply and see that they have a recommended psi. Unfortunately I can't find any of the "special tools" that are recommended for these tests. Even our Cummins timing set has been non existant in the seven years I've been working where i'm at (someones departing gift I imagine). Any ideas on what to look for? I'm down to either a fuel issue or bad turbo. On a side note I did remove one intake bolt and put a gauge on and test drove it. I could only achieve around 10psi of boost.

....I have also removed the fuel filter and checked for fuel flow. it delivered about 200ml in 30 seconds of cranking if this tells anyone anything.

Sounds like low fuel pressure.
The "special tool" is nothing more than a injection pump inlet banjo bolt with a 1/8'' port tapped into it to connect a hose with pressure gauge. Either tap it yourself and plug it when finished or just replace the overflow valve with a new one as it is likely the problem.
Recommended fp is 22-28 psi at idle but 18-35 is fine.

Either tap it yourself and plug it when finished or just replace the overflow valve with a new one as it is likely the problem.
Recommended fp is 22-28 psi at idle but 18-35 is fine. [/B][/QUOTE]

I would certainly be looking for low fuel pressure if you only get 10 psi of boost and no black smoke. I agree with infidel, the overflow valve is cooked. If you have one handy, I would just put it in without checking much else. There is not much else to go wrong if you have adequate fuel flow right up to the injector pump.

just my .02

Thanks for the input. I've ordered the part and will let you know what happens. This truck has 360K on it and is still in pretty respectable shape for a work truck. I also worked on another good customers truck this week, one that I had tried to buy off him for a number of year. It's a 95 with 212K on it now. Gotta respect the durability of them 12valvers.

I devised a bolt to test the fp. It was all over the board and low. Installed the new overflow valve and that brought the numbers up and now they are steady. At 2500 rpm it had 27psi which is the low side of the spec, but still passing. Drove the truck and it still lacked power. Wasn't able to monitor boost as my boost gauge bounced off the floor yesterday. I do have a spare turbo for my 01 I could try on it, but I just don't believe it's a turbo issue. Thank god it's slow right now cause I'm sure not making any money on this one!!

Seems like you've covered the likely, I'd check the valves and timing next.
Also if it has over 80k the cat is probably clogged up.

I just fixed the problem on my '94. The waastegate actuator is blown out. What this causes is the diaphragm in the injector pump to not actuate. This causes a power loss because the diaphragm is what delivers fuel but the reason it is T-ed into the turbo is so that the truck doesn't get fuel before it gets boost. the reasoning for boost before fuel is smoke. This almost eliminates smoke under normal driving to reduce emissions. The way to fix it is to plug the line that goes to the wastegate actuator and see if it fixes it. If it does, replace the wastegate actuator and let us know if you get 'er fixed.

Check the fuel shutoff solenoid. had one on a customer's that was worn and would get cocked as the plunger tried to pull up, and would not pull the lever up all the way. It would start and shut down fine, but felt real lazy, and would not make over 15 psi boost. I also agree that you should pinch off the wastegate hose and try it. It's amazing how much boost they can leak off.

PS- Whaddaya mean "dark ages trucks"?!?[laugh]

I'm with torquefan I got a 95 550,000 miles I'd say wastegate and or fuel shutoff solenoid I'm in the business those repairs can be frustrating
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