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?

Originally Posted by turbo2332 View Post

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.

turbo2332...I see your point, I think I had pre convinced my self I would have 19ish psi before I put the gauge in. I freaked me out when it would not show any boost until 1500rpm. To put the motor under a load I pointed it up a 5% grade and WOT, but I dont think i had enough time at WOT to really see what the boost would bild to. On some practice freeway runs it did make 15psi but I was doing 80 and had to back off. The baby does get moving without hauling anything around. I think I should load up the truck with a ton in the back and give it another try up the hill. What I think I am looking for is a earlier spool up. the turbo spins freely and has no play. I checked all the boots. I dont know how to test the intercooler to see if it was damaged by the previous owner. does your truck build boost sooner than 1500rpm ? I do have a boost elbow and fuel plate from Dynomite Diesel. I'm afraid that if I dont get more air the added fuel will just make smoke.

I guess my question is: can I have the boost a little earlier, if it builds 20psi but not till 2700 rpm, i would not be able to use it much. the main goal is to haul a 8k tailer over the tahoe pass 7% grades for miles, I have a 2800 mile loop threw NM, UTAH, CA.

rx7man...The airfilter is clean...ish, Im not shure im reading the filter minder correctly. do you think it will hurt anything if I run without a aircleaner for a test run only? thease old airboxes where not well designed. I think i should after market it. The truck is a 2500 with 1 ton booster springs over the 3/4 ton stock springs, and they are cranked up tight. with a ton in the bed it rides leveland feels like a cadillac, all the other time its a back breaker, kidney rupturer. I'm working on that too. The TC lockup switch I added because the TPS was dirty and I couldnt aford a new one "$150" from the dealership. Warning!!! when adding your own TC lockup switch mark the on and off position before trying it out. pulling out of the parking lot and it lockup shocked the hell out of me...and killed the motor, hope i didnt hurt the tranny. I'm looking into if something is holding the waste gate open a smidge.

Insubordinate....how early did your boost come on?

thanks everyone I'm learning TONS!!, mostly how much I don't know. I've been reading this forum for a while but for everything I'm NOT working on, but I might have to work on one day.

my truck doenst start making boost till much later. i have a bigger turbo than stock. to make boost come on harder quicker you have to generate drive pressure. which is the force that gets the turbine moving. RPMS and kinda heat is this force, so without making more of those sooner you will still have a turbo that seems kinda slow. a hx35 is a very fast lighting turbo however. i highly reccomend some govenor springs. 3k or 4k doesnt really matter. hey are the best bang for the buch and you will feel like you are driving a totaly different truck.

thanks turbo2332, i'm gonna go with your suggestion on the gov springs. do you think that turning down the stock gov spring 3-4 clicks is a good idea? or comparable to changing springs? ($150 is still $150, but ive been feeding my kids too much lately anyway, and we gotta have priorities) since i should make one mod at a time the gov. spring looks like a good place to start.

thanks for all your help

feeding the kids to much... thats funny

you can tighten the stock springs but if wont really give you that much. do the springs and a boost elbow at the same time.

I totally agree that a 3K governor spring kit makes a night and day difference in the way the vehicle feels, and it doesn't increase peak torque, so it's probably not too bad for the auto tranny, with a 4K kit (OK, so it's more fun), the truck gets jumpy and you need to put heavier valve spring in as well to prevent valve float

In my truck, which fuels a lot harder (that helps spool the turbo), it's kinda slow coming up to 10 PSI, but somewhere around 1300-1500 RPM it'll make about 15 PSI, but from there to 1700, it'll make 30... I've been thinking of taking a vid of it for a while.

The thing about diesels is it's the fuel that makes power, and it's the fuel that spools the turbo, you need air to burn it evidently, and the air cools things, like EGT's

Johnny, you said you had guages... is an EGT one of them?

Oh... I remember when I got my truck it was only making 10 PSI, it made really quick, but only 10 PSI... then I found the guage was sticking when I put a new guage in and I was actually making 28 psi at the time... Are you sure your guage is calibrated in PSI and not something else?... Hey, I've really got more questions than answers at this point but listing some possibilities that I'm sure *someone* has seen

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I type too slow... you could also back off the star wheel in the AFC a bit, I can't remember which direction is backing off though, that would help fuel a bit harder down below.