Hi all, I just installed a set of gauges so i can start hot rodding my 94' 12v. but i am getting lower than expected boost readings. 2 psi @ 1600 rpm, 4-6 @1750 10-12 @2000 topping out at 13-14 @ 2200. also it shows no boost in park, even when at 2400rpm, is this normal? i love this truck but im still learning. if it helps i just drove it 3000 miles with pretty bad gas milage...avg. 15mpg with no trailer. any and all help, especialy snide comments are welcome

truck is a 94', 12v, 195,000 miles, 4" strait exh., gauges, TC lockup switch

 

my 95 gets 15 coming or going. your boost numbers are fine. you will never see boost in park or neutral because the engine can eat everything the turbo makes, its not working.

 

the numbers you list... are they while you're driving?? by about 1700 rpm in a higher gear I think you should get about 15 PSI mimimum.. I think the factory setting is somewhere in the vicinity of 20 psi.

if, while driving, you don't get somewhere close to that, I'd look for a CAC (aka intercooler) boot being broken... especially the ones near the bottom.. if the truck has ever had front end damage, the inner fenders like to rub on them and put holes in them.

You can also take the air cleaner hose off the turbo and see if there's much shaft play... there is always a little bit, but if it flops around, you have a problem

 

thanks for the fast reply, while i was waiting i when out and checked all the boots (even pulled the bottom ones), tightened every thing down.

turbo2332, thanks for the reassurance, and for the park/neutral info

rx7man, I checked all the boots, the lower CAC boots are ok but are very soft, the truck did have repaired front end damage when I bought it....15psi @1700 rpm in high gear is what i was hoping for

The turbo spins nice and no play, I guess I need to start installing the fuel plate from Dynomite, and add boost elbow.

any way to "up" the boost a little sooner in the power band?
thanks for all your help

 

If all that is good... I'm wondering if something is holding the wastegate open... Perhaps in the front end damage, the wastegate actuator bracket got bent?... try wiggling the wastegate control lever... if there's play (that is, the actuator doesn't really pull back on it), I'd guess that the bracket is bent or something is a bit haywire mechanically...

you can try just disconnecting the wastegate line (plug it toward the intake manifold) and take it for a test drive.... if it behaves a lot different, a boost elbow will help you out a lot, if it doesn't make much of a difference, you still have issues elsewhere. Just watch the boost guage on the test drive when the wastegate is disconnected... these trucks just start to make power at 15 PSI, and the boost will rise from 15 to 30 in a very quick hurry (if it fuels hard enough). On this test drive... keep the boost at 30 PSI or less... get onto the throttle in little bits and be ready to back off.


Have you made sure that your air filter is nice and clean, and there's nothing restricting the airflow into the airbox somehow? does the filterminder read OK? I just have to ask.. sorry

 

Rx7man...that was a great idea, to check the waste gate actuator....I will get right on plugging the waste gate line on the intake side, and take it for a test drive
you rock dude....by the way are you running the stock turbo on your dually

 

stock these trucks are gated from 17-19 psi. you CANT get 30psi without blocking the wastegate which is FAR from intelligent unless for testing purposes ONLY or by installing a boost elbow. you will not see over 20psi if your truck is stock.

 

^^This^^
Wastegate is at at 17psi. Your psi reading look fine. I used a boost elbow in my 97 (pretty much no wastegate) and could only pull 25psi MAX. I had to add more fuel (fuel plate) to see more than 25.

 

a boost elbow isnt like running without a wastegate. it retards the reference to the wastegate allowing it to build more boost before the gate opens. i hit 52 with an overfueled stocker once. LOL

like blowing through a 1/2 in pipe vrs blowing through a straw. it takes longer to move the same volume of air through the straw but eventually the exact same amount will be present, that is a boost elbow.

 

yeah... I couldn't remember what the factory wastegate setting was...

and no, the boost elbow is not just retarding the signal, it's limiting what the wastegate sees, as a percentage of the manifold pressure... If it were just a restriction, you'd have a boost spike, then it would settle back down to the factory wastegate setting.

I heard that the stock hx35 can handle a peak of about 32 PSI, and I'm pushing that limit... Anything above that it just becomes an air heater.

Actually, since Johnny's truck is fueling at a stock rate, he probably wouldn't hurt anything running without a wastegate, but probably wouldn't get any benefit from it either.

Yes, my truck is still running the stock turbo... Looking to put a Super B on it... but I spent enough on it this year.

You never answered the question of the air cleaner, etc being clear.. and the FilterMinder reading OK...

one more thing.. what gearing is in this truck? is it a 2500 or 3500? If it's a dually like mine with 4.11 gears, I don't think your fuel mileage is terrible... I get about that, whether i'm loaded or unloaded... If it's a lighter truck with higher gears I'd expect much better.

What I find off about your boost is that you should have 17 PSI much earlier... the fact that you have to get to 2200 RPM for a peak boost of 14 PSI... *something* seems up to me... if it's not a clogged air filter... a bad exhaust leak before the turbo or a restriction after it... That thing should produce 15 PSI by 1500 RPM if you ask me

I see you have a TC lockup switch... is that because it has an exhaust brake? could that be messing up somehow? as in not opening properly?