Low Boost, what's up?

[TurboDiverArt]

OK, now that I

[TurboDiverArt]

OK, quick update from today:

Drove the truck for the first time on the highway since installing the X-Monitor. Towing nothing but with the AC on low up a good grade had trouble maintaining 70 MPH. Trans temps went to about 190-200 (upper line, pre coolers), EGT's to 940 (post turbo) and cooling to about 210. This was a good long grade, probably 5-6 percent for about a mile or two. Temp outside was about 80-85 and not humid. I was surprised at this. Boost registered around 2.5 psi. I didn't have it to the floor but probably a good 3/4 throttle. I hit the above numbers at the top of the hill and was about to start letting off. I don't believe the trans unlocked the converter or dropped out of OD (3:73 gears). I ended up slowing to 65 as I couldn't maintain 70 MPH without really standing on it and I didn't want to do that. Once I cleared the hill everything dropped to normal, EGT's were in the 450-550 range (post turbo) at 70 MPH, trans temps dropped to about 170 and boost as usual at cruise was 0.0 and engine temp at about 195 which matches the Robershaw therms. The coolant is fresh as if the trans fluid, oil has about 2500 mils on it and will be changed this weekend. I have a shift kit to install but I

[a5150nut]

The grill, should be able to find all the screws in it. Parking lights probably have to come out. Probably 3 or 4 small bolts/scews accross the top. You should also remove the top half of the fan shroud so you can blast with water from the fan side.

It would probably help to loosen the oil cooler too. Be carefull of the vanes, they bend easy and tubes cut easy on the radiator. A stiff brush works to streighten any bent fins.

I use black nylon sceen behind my grill to keep bugs out of the radiator. :rolleyes:

[TurboDiverArt]

Originally posted by a5150nut:
The grill, should be able to find all the screws in it. Parking lights probably have to come out. Probably 3 or 4 small bolts/scews accross the top. You should also remove the top half of the fan shroud so you can blast with water from the fan side.

It would probably help to loosen the oil cooler too. Be carefull of the vanes, they bend easy and tubes cut easy on the radiator. A stiff brush works to streighten any bent fins.

I use black nylon sceen behind my grill to keep bugs out of the radiator. :rolleyes: Thanks for the info!

I have only owned the truck for about 5000 miles, don't think the previous owner had a grill screen. I bought a winter front that came with a summer screen. I need to find it and put it on. I had looked and I did see some bees and spiders stuck in the cooler fins so I know there is stuff to clean out. I don't know if that will solve all the problems but it can't hurt. I usually use a soft small brass brush (looks like a tooth brush) for fine cleaning. I'll probably do that to clean and straighten any fins.

Thanks a lot for the help on the grill. You think the screws I see on the top are the only ones? I assume it can

[whatnot]

Did you try bypassing the wastegate solenoid? If that doesn't give you at least 15 PSI of boost under full throttle and/or and SES light, there is something wrong. (mine will instantly peg the 15psi gauge if I do it)
Do you still have the stock exhaust on it? If so, it has a cat doesn't it? If so, it might possibly be plugged.
Do you have any exhaust leaks? I have seen the flange rust off on the crossover pipe on 2 different truck right at the exhaust manifold. (driverside on both) They were older trucks than yours though.
What about the airfilter? A restrictive one will limit boost.

[TurboDiverArt]

Originally posted by whatnot:
Did you try bypassing the wastegate solenoid? If that doesn't give you at least 15 PSI of boost under full throttle and/or and SES light, there is something wrong. (mine will instantly peg the 15psi gauge if I do it)
Do you still have the stock exhaust on it? If so, it has a cat doesn't it? If so, it might possibly be plugged.
Do you have any exhaust leaks? I have seen the flange rust off on the crossover pipe on 2 different truck right at the exhaust manifold. (driverside on both) They were older trucks than yours though.
What about the airfilter? A restrictive one will limit boost. I have not tried bypassing the wastegate. I think before I do that I want to test with a mechanical gauge so I can rule out the X-Monitor having incorrect readings.

I do have the stock exhaust but the CAT is hollow. No exhaust leaks that I know if. I'll have to look closely at the cross over.

I have a Uni foam air filter. It's got about 4000 miles on it but it is dirty. I think I need to clean the intake tract. That's on the agenda for this week when I change the fluids.

Thanks for the info!
Art.

[TurboDiverArt]

Quick update. I hooked up the mechanical gauge this morning and I am in deed producing only 3 psi of boost at the upper manifold pipe (where John Kennedy suggests putting it). I did some additional checking. I checked the vacuum at the wastegate. At idle (600-700 RPM) I get 15-16 psi of vac. If I bring the idle up to 1100 RPM I register about 17 psi of vac. If I bring the idle up to 1500-2000 then the vac drops to about 10-12 psi. This is with a Tee in the wastegate so the wastegate is functional. I realized I probably should have tried it with the wastegate not in the system and read just vacuum from the pump ruling out the possibility of a leaking wastegate. The Vac seems low to me but what do I know? At highway speed, would 10-12 psi of vac be enough to hold the puck shut? What

[MTTwister]

"T.D.Art" - the Grille - mine's a '96, but this weekend I was able to get some screen behind it. I have a grille-brush guard, so... I undid the 4 visible screws - two ends verticle, to middle horizontal. Then there's a screw in the dead middle that bolts in/around the Horn ( or the latch support bracket.) I was able to pull the grille far enough forward to get aluminum screen between the grill and everything else ( piece = 36" by 16") ie I didn't need to pull the headlights to get this far. Do have some nasty scratches on the arm from working it in there, lots'a stuff for it to hang up on..

But I believe you may need to pull the parking lights to remove the whole deal, and there looks like another screw in the middle bottom that has to come out. 7 - 8 mm's I believe.

I need to pressure wash mine from the inside out too.Hope I can do that without full dis-assembly!

[Bobbie Martin]

The bottom of the grille is held in by snap in clips. You do NOT have to remove the screws on the bottom. Just look close and you will see the clips, you may be able to release them by hand or with a small screwdriver. Park lights are easy to remove and the bulb holders just unscrew. Headlamps do not need to be removed. Grill removal is 5 minute or less job once you figure it out.

[gmctd]

Art, to determine if the vac pump is ok, you need to take readings off the pump, not the wastegate.
It's ~24-26" at idle.

The PCM is always modulating wastegate vacuum, from 63% at idle and ~65mph, to down around 20%, lowest I've seen it, at full throttle acceleration, say from 45 to 70mph, in overdrive.

PCM is not trying to assist you, it is limiting your quest for power, to the tune of 7-8psi Boost, max.

The limits are more than likely warranty and emissions considerations.

Vacuum you are seeing is normal, but Boost seems low, unless that's under normal, vehicle not loaded, driving.

Accelerate from 50 to 70, such that the trans stays in overdrive - you should see 7psi boost with that demand.

Wastegate actuator has 12"vac on control side, which means Baro is exerting 12", or 6psi on a diaphragm of roughly 3.14sq in area - the wastegate is forced closed by about 18psi, the actuating arms being equal length.

What shape (literally!)is the downpipe in, between turbo flange and exhaust pipe flange?
Most apppear to have been installed with a jack-hammer, severely limiting exhaust flow, and would cause increased exhaust backpressure, limiting Boost.


333333333

[TurboDiverArt]

I have boost!!

I guess the leaking vacuum was my problem. Now I register 6.5-7.5 full throttle. Cruising at 70 MPH I