Greetings!

I've spent a couple of days searching, but haven't found the answer I'm looking for. I recently traded my '95 F250 PSD on a 2000 F250 PSD 6spd. I installed boost and EGT gauges, and was only developing around 5 lbs of boost. I checked all the intake fittings and found a loose clamp. After tightening that up, I am able to pull 10lbs in 4th and 5th empty on level ground (at 4000 feet). I have double checked all fittings and the boost line. With the wastgate actuator line disconnected and plugged, it will pull 15lbs. The truck is totally stock, except for Kwikk's filter mod w/ the 6637 filter and has around 110,000 miles. The stock airbox was not sealing well, but a visual inspection of the turbo seems OK, and it spins easily. I did replace the fuel filter, which was dirty, but that didn't change the boost. If I understand correctly, stock boost for this truck should be around 17-18lbs with the wastegate line connected. Is that correct?

I'm wondering where I should head next to diagnose the problem? What should I check as far as the fuel system? Is there anything else to check as far as the turbo?

Thanks!

 

you should be making more than 15 psi with the wastegate disconnected. you said you checked all the clamps on the intercooler boots, check the boots them selfs they can sometimes split. also you need to check the clamps and boots on the intake manifolds (under the turbo where they go into the heads). how is the power, does it seem good or is it real doggish. what are your EGT's when you get on it, if they get high fast you could have a blockage on the exhaust side, EPBV (exhaust back pressure valve) not opening, or a clogged cat if you have one.

 

At what RPM should you be making 15psi? On my truck cruising the interstate at 70 with no load I am making about 5psi at 2000 rpm. When I am accelerating from a stop with no load I am making 10psi. Should it be providing more boost than that?

 

at WOT (wide open throttle) a stock PSD should make 17-19 psi of boost. from a stop, put your foot to the floor, but the time your in second gear you should see that much boost

on edit: i just looked at you sig, with the tymar, 4" exhaust and 10k mod, you should be making around 20psi

 

EGTs are lower than my 95 in comparable situations. The EGTs do not come up very fast. I have inspected the I/C tubing boots and they look OK, and I tightened the clamps on the intake boots, although I have not removed and inspected them. Will the EBP valve cause low boost w/o raising EGTs? There is no cat on this particular truck. I'm really wondering if it is a fuel problem, although the wastegate seems to be limiting it to 10lbs which doesn't make sense?

 

if the ebpv was sticking shut you egts would would run high. you can try unhooking the wastegate. disconnect the red line that goes to the gold canister on the top of the turbo and plug it onto one of the IC boot clamp bolts. they take it for a drive and see what you get.

 

Tried that already, but it should be up there w/o disconnecting the actuator. I'm wondering what would cause the wastegate to open at 10lbs? Bad actuator?

 

the wastegate is purely a mechanical device, there are no seosors or electroinc signals that tell it when to open. the red line sends manifold pressure to a diafram in the actuator that pushes it open, there is also a spring in the actuator that will allow the wastegate to be pushed open by pressure in the exhaust housing of the turbo at around 25psi.

back to a question i asked before, how does the truck run? if it was only making 10 psi of boost at WOT it would be a pig. i would guess you either have a leak somewhere or the gauge (for what ever reason) is not reading correctly

 

The truck drives well, but my '95 was more responsive. It was lighter and shorter geared, however. I understand the wastegate actuator works off manifold pressure, but if it's opening at 10lbs, there must be a problem with it? Spring or diaphragm?

The gauge is a brand new Autometer. I guess there could be a problem with it, but I would think that would be a low probability.

 

if the diaphragm (boy i butchered that word) was bad it would be just like the wastegate was disconnected. i have never heard of a spring going bad but i guess it could happen. if the spring was adjusted real weak that coud cause it.

if you havent already try to test your boost gauge. if you have an air compressor you can set it to say 20psi and pressurize the line( disconnect it first)from where it taps into the map line (if thats where you installed it) to the gauge. see if it reads right and see if it bleeds off pressure. at least buy doing that you will know if its the gauge or not. as far as it being a fuel problem, thats hard to say, i would think if it was you would be experiencing other problems as well, and not just low boost. from what i have seen most low boost problems have to do with the turbo, intercooler, intercooler tubes and boots, or a backpressure issue in the exhaust

 

Were is your boost line connected to the intake?

 

The boost signal is tee'd off the MAP sensor line.

 

That's not entirely correct sir. The pressure line that opens the wastegate is routed through the wastegate control solenoid, which is controlled by the PCM. When everything is hooked up and functioning the PCM will commad the wastegate start to open (STO) at 5 psi. That's how the PCM "limits" the turbo to 16-18 psi when there is generally enough stock fuel to support 20 or so with it disabled.

RodanAZ,

With the manual tranny you won't see your max boost until you pin it to the floor in 5th or 6th. Also, it's possible that your wastegate was not set correctly at the factory. In that event you would need to shorten the wastegate actuator rod to apply more seat pressure to the wastegate.

Can you elaborate on "the EGT's don't come up very fast"? How high will they go, and how long does it take to reach the max EGT?

 

I honestly wasn't watching the EGTs that closely, but they weren't overly high (not, for example, as high as the '95 would have been under the same conditions). I'll run it again for EGT numbers when I get a chance. I was pinning it in 5th and 6th, up to around 2700 rpm, empty, on level ground, 4000 feet altitude. If y'all think 10lbs is normal under those circumstances with the wastegate functioning, then maybe I'm making a mountain out of a molehill...if it's supposed to make 17-18, then I've got an issue somewhere...

 

10 psi is not normal, but if the EGT's are too low it would point to a fuel delivery problem. Does the truck bog down, or does the power flaten out real bad when you romp on it? Difficult to gain any speed in a passing situation for example. These were the symptoms my truck had when my fuel pump started failing. There could also be an obstruction in the fuel lines, or in the pick-up in the tank.