Low boost?

[bjytech]

I'll start this out by saying that the other week I installed gauges (Boost and EGT). I was told that for my truck with whats done to it I should be able to make 35psi boost easy but the most I've seen is 28psi and that was accelerating up a hill giving it all its got in 4th gear. So I decided to check for boost leaks. Tonight I did a pressure check at 6psi and all the intercooler boots and everything seemed fine. Then I noticed the oil dipstick was hissing a little so I take it out and the air is somehow leaking in and coming out there. Would this happen because I did the pressure check wrong? Are you supposed to block off the one end of the intake when you check it? Is this happening simply because intake valves are open? Or could there be some other cause?I may sound a bit stupid... but hey, there's no stupid question right? A guys gotta learn sometime.All your advice will be much appreciated!Also one more thing if anyone knows. On the gauge there is an orange wire for the dimmer, but the instructions don't tell you what to hook it up to for it to work. So if anyone could tell me where to hook it up to that would be great.Kinda a long post but hopefully everything is clear for you guys, if not just ask what you want to know.

[MnTom]

That hiss would be air being blown through an intake valve and by a piston. Chances are it is nothing to worry about. Another place to check for leaks is the top of the intake itself. When you have pressure on it check the grid heaters and the top plate on the intake too. What is your waste gate set at?

[bjytech]

I checked around the grid heaters but I didn't really check the plate on top of the intake so I'll have to do that when I get a chance. My waste gate is wired close. When I got the truck the waste gate articulator was stuck open so I just got rid of it and ran with the waste gate mostly closed till I got the gauges a few weeks ago, then I made sure it was closed completely.

[ELKSLAYER]

Did you change the bost elbow or is it stock. If it is stock you wont get 35 psi of bost.

[bjytech]

Did you change the bost elbow or is it stock. If it is stock you wont get 35 psi of bost.

My waste gate is wired shut so if I understand the boost elbows function correctly its irrelevant to me.

[Mopar1973Man]

Well it seems to me you good for the air side but you might need to do some adjusting to the fuel plate.

[MnTom]

Does your truck smoke at all? If you are seeing black smoke you have air issues, but if you don't have smoke you are not getting enough fuel to get to 35 psi.

[bjytech]

Well it seems to me you good for the air side but you might need to do some adjusting to the fuel plate.

I'm running with no fuel plate and the AFC is gutted now too.

Does your truck smoke at all? If you are seeing black smoke you have air issues, but if you don't have smoke you are not getting enough fuel to get to 35 psi.

I can make it smoke anytime I want since I gutted the AFC. Later today my needle valve is supposed to be in at Napa so once I get that I'll be able to install it and check my fuel pressure. about a year ago when I had some work done on the truck they checked the fuel pressure and it was at 17psi at idle and they said it was ok so I just left it.

[MnTom]

Well then, have you checked the inter cooler for any leaks? Another thing to do is pull the intake off the turbo and check to see how it feels when you spin it. Also check for play on the shaft. A little end to end play is fine, but if you get side to side and can make the compressor wheel touch the side you have a problem.

[ISX]

You have the same thing as mine, no fuel plate, no afc, both 215HP 5spds. If I clamp the wastegate I can get to well over 40psi. I wonder if you have a fuel restriction. A dirty fuel filter/bad lift pump/bad overflow valve/etc. can all degrade it.

[bjytech]

Well then, have you checked the inter cooler for any leaks? Another thing to do is pull the intake off the turbo and check to see how it feels when you spin it. Also check for play on the shaft. A little end to end play is fine, but if you get side to side and can make the compressor wheel touch the side you have a problem.

The turbo was one of the first things that I checked and it spins nice and no play in the shaft.

You have the same thing as mine, no fuel plate, no afc, both 215HP 5spds. If I clamp the wastegate I can get to well over 40psi. I wonder if you have a fuel restriction. A dirty fuel filter/bad lift pump/bad overflow valve/etc. can all degrade it.

I think now I may be a fuel problem. I didnt get the needle valve that I need to hook my fuel pressure sender up today because for some reason napa didn't get it in their delivery. but tonight while driving the truck I just let it have it in 4th and it smoked up till 2000RPM then it starts to go into a haze then close to 2300RPM it doesn't smoke at all. Hopefully when I go into town tomorrow napa will have the valve and I'll have pickup a fuel filter too, always good to have one on hand anyway.

[MnTom]

Hey, just a thought, but have you checked your pre-screen? That is one spot that gets missed that may be part of the problem.

[Mopar1973Man]

about a year ago when I had some work done on the truck they checked the fuel pressure and it was at 17psi at idle and they said it was ok so I just left it.

http-~~-//www.youtube.com/watch?v=YgSuH9txH4U

[bjytech]

Ok Napa had the needle valve in today so I got my fuel pressure gauge install and at idle (about 650RPM for me) I have 13/14psi and the highest I could get it is was 22psi, so then I clamped the return line and it went up to about 30psi at idle so I guess I need to order a new overflow valve.

[ISX]

I forgot I had made an article on this. http://mopar.mopar1973man.com/cummins/2ndgen12v/p-pump/p7100-fuel-pressure.htm I also forgot I put that plug in that banjo bolt, I have been looking for it all month

[bjytech]

Ok so last night I ordered a new overflow valve. To get me by till I get the new valve I took my overflow valve apart and stretched the spring to about 15mm and put it back together. I was then seeing about 28psi at idle and the overflow valve seemed to be popping open at about 36psi. After driving it today though its gone down to 25psi at idle and popping open at about 33psi so according to that drop after just driving it for a few hours today its just a temporary fix but it will do till the new valve comes. When accelerating hard in 4th once I hit about 1500rpm I'm making about 15psi boost then it shoots up pretty fast to around 25psi then it just kinda dies out so I'm not sure whats going on I'll have to check my wastegate again and make sure its not opening any under the exhaust pressures. I did notice however that the truck doesn't seem to work as hard as it used to going up hills.

[bjytech]

OK so another update. Saturday I got the new overflow valve from LarryB and installed it then I cleaned the pre-filter screen and then re-wired my wastegate shut again getting the wire as tight as I could. Now I see up to about 30psi boost and fuel pressure at WOT is 21psi. It drives almost like a different truck now :thumb1:But I get one thing fixed and theres 3 more possible things to fix now :duh:While re-wireing my wastegate I found that my head gasket is leaking a little coolant out above the water pump/behind the alternator so that needs to be fixed and my left front wheel bearing seems to be squeaking along with another noise that I think seems to be coming from either my throwout bearing or the pilot bearing... theres always something

[ISX]

You still have issues. Your fuel pressure should never drop below 25psi when you are under a load. Mine never drops below 30 under a load. At idle I am at 18 or so. A clamped wastegate with no plate or AFC should send that turbo well over 40psi. I think you said you changed the fuel filter, did you check the screen on the fuel heater? It sounds like it might be a combination of bad overflow valve and bad fuel pump.

[bjytech]

I checked and cleaned the screen on the fuel heater but I didn't replace the fuel filter yet because I didn't have the money on me to get one when I picked up the needle valve, but its time for a oil change and new fuel filter so I'll do them at the same time. This morning I went out to check some things and found out that yesterday I was making that 30psi of boost with the wastegate doing whatever it wanted because the wire slipped off it, so I'll have to put the wire back on and fix it so it doesn't come off and see what I get.

[ISX]

I checked and cleaned the screen on the fuel heater but I didn't replace the fuel filter yet because I didn't have the money on me to get one when I picked up the needle valve, but its time for a oil change and new fuel filter so I'll do them at the same time. This morning I went out to check some things and found out that yesterday I was making that 30psi of boost with the wastegate doing whatever it wanted because the wire slipped off it, so I'll have to put the wire back on and fix it so it doesn't come off and see what I get.

That sounds right then. With the wire off, the wastegate will blow open the entire time. It is supposed to open at 23psi but with no plate or AFC, you end up outflowing the wastegate and building 30psi. Fuel pressure is still a little low though, maybe the fuel filter will fix it.