I am having a under boost issue but with no fault codes. Car is blowing black smoke and in limp mode. I have checkes all vacuum hoses. From vacuum pump to the N-75 valve, I have 28ibs. coming out of the N-75 valve to actuactor I have 20ibs.Back up a bit. What problem are you having that you are trying to correct?
The MAF and the N75 are both wired to the ECU, the MAF is an input, the N75 is an output. If either one had a wire problem, the ECU would have a DTC to that effect. Many times a low boost problem will also be accompanied by a 'MAF implausible' type DTC, along with some sort of 'boost deviation control range not reached' type of DTC. A boost leak somewhere in the charge air tract is the likely cause there.
this is my original post on this ongoing isssue. hopefully reading this will help you better nunderstand my issue.You cannot have low boost without a DTC. Have you mapped actual and requested boost as you drive the car?
Car blows black smoke and is in limp mode. I unplugged the vacuum line from turbo actuator. Car quits smoking and will accerate but it still has no boost.You cannot have low boost without a DTC. Have you mapped actual and requested boost as you drive the car?
Yes I have checked cam for wear, it looked good and I also have unplugged the MAF and plugged it back in and no change. I checked the VNT screw and it was adjusted properly but I lenghthened rod so it wouldnt pull up so far to see if it would help. took the car for drive and at first it had a lag then it started boosting up but continued to blow black smoke. Does this mean that my turbo is bad?I'll second the need for a scan and monitoring manifold pressure, its hard to work blind. You also can't have "limp mode" without a code set.
Have you checked the cam for wear?
Given the symptoms, I would also check for a stuck open EGR valve flooding the intake with exhaust.
MAF can fail but not set a code. Unplug it and restart the car. If it runs better it may be the problem. Unusual on a BHW though.
Could also be a very badly adjusted VNT stop screw, usually this problem develops slowly as the VNT linkage wears. If the VNT vanes are allowed to close too far, exhaust manifold pressure will spike and there will be too little exhaust flow to spool up the turbo. You'll get smoke and misfiring but usually you can push though it and the engine will eventually rev up.
What is the history on the problem, did it develop suddenly or slowly?
Vacuum to the N-75 I have 28lbs. mercury to the N-75 valve. Coming out of the N-75valve I have 20lbs. of mercury to the actuator. I have tested the actuator. It holds vacuum. I hooked up an air vacuum gage to the N-75 valve and it holds a steady vacuum of 28lbs. I understand that the vacuum above 1000 rpm should drop to 0 lbs. Vacuum does not drop until it is above 2000 rpm and then its only breifly the drops back to 28 lbs. I have not checked the volts coming from the ECU to the N-75 valve. What volts should I have to the N-75 valve?Again, any history?
I have my doubts about turbo failure, it's rare on a BHW. Pull the intake hose and give it a spin, if the shaft turns freely and does not rub the housings it's probably ok.
Well back to the drawing board. pulled hoses and inspected each one. found no holes or spots that are questionable so this is what I did.Yes, you have a boost leak, and the DTCs show this. See, wasn't that easy?
Charge air hoses are the most common... there are four of them. Turbo-to-crosspipe (most common), crosspipe-to-intercooler (never seen one of those fail), intercooler-to-firewall tube (rarely fail), and the little elbow from firewall tube-to-throttle flap (second most common).
Look for oily trails, and/or have someone brake torque the car briefly while you listen for the hissing. It should be pretty obvious.
Have you done this?Yes, you have a boost leak, and the DTCs show this. See, wasn't that easy?
Charge air hoses are the most common... there are four of them. Turbo-to-crosspipe (most common), crosspipe-to-intercooler (never seen one of those fail), intercooler-to-firewall tube (rarely fail), and the little elbow from firewall tube-to-throttle flap (second most common).
Look for oily trails, and/or have someone brake torque the car briefly while you listen for the hissing. It should be pretty obvious.
Yes I have checked for oil trails and have found none so far. Power braked car and cant hear any hissing sounds. I have also watched the actuator and it is working properly. Turbo is boosting and hoses are holding pressure but car is still setting codes and going into limp mode and blowing heavy black smoke after a couple of minutes of this.Have you done this?
You say that it's still a leak but I have pulled all hoses and inspeacted them. I also made a pressure testor with a schreader valve. I capped both ends and aired system to 15 psi. System held pressure for over 5 minutes until I released it.Well it still sounds like a boost leak issue to me. I could probably find it within a few seconds if the car was here in front of me.
Unless the camshaft is tooefed, but that is usually a different situation, and it will run poorly all the time and have a dead cylinder.
And you've checked it sounds like control side vacuum, which thankfully on the BHW is brutally simple. Just that the N75 is in a bit of a fiddly location. But the actual vacuum system is easy to check.
Only history I have of the car is that it has 300k on odometor and that motor was rebuilt about 45 thousand miles ago. Thats all I know.Whatever went through the turbo may be in the bottom of the intercooler, mouse nest, rag, whatever.
And for the fourth time, what is the history? Did you buy it like this? Did it develop over time? Did it come on suddenly?
Do you mean that the OP drove the car to you from Oklahoma City?Well I got this one licked. Jesus, what a mess.
Can't say I have seen this many things wrong with one car.... and I never even lifted into the air.
Oh no, this thing couldn't make it across the street under its own power before, LOL. It was towed here.Do you mean that the OP drove the car to you from Oklahoma City?