Low boost problem

[edbaus]

Hi,

I have an 87 944 turbo. All original. Just bought it and just got it running. Had a bad fuel pump.


The boost only goes up to 1.2 to 1.3 (.2 to .3) and does not go any more.

I gave it the blink test and there are no trouble codes to see. I pulled the TPS plug off just to make it throw a blink code and it did, so I know the KLR is working and I have the LED hooked up right.

I went through and checked all of the vacumm lines and fixed any that looked suspect.

I crimpped off the line to the wastegate and there was no change. Still maxed out at 1.2 - 1.3.

I pulled the blow off valve off and checked to make sure it is completely closed and it is.

So, where should I look next. What is the next most likely issue. Pull the plumbing apart between the turbo and the intake and inspect it all ?

Other than that, the wastegate itself ? Any good way to check ? I guess the old, check to see if the wastegate exhaust pipe gets hot trick.

Thanks

Ed

[mitfa911]

I would think that your car might have a clogged catalitic or worst case scenerio a collapsed exhaust pipe before catalitic.

[nize]

Originally Posted by edbaus

I crimpped off the line to the wastegate and there was no change. Still maxed out at 1.2 - 1.3.

troubleshoot why the wastegate isn't holding boost first;

1) check the vac line between the cycle valve and the wastegate using a hand vacuum pump, insure it holds pressure/vacuum and is not leaking.

2) visually inspect the wastegate, make sure it doesn't appear leaking exhaust.

3) visually inspect the exhaust manifolds to wastegate, make sure it doesn't appear leaking exhaust.

my bet is the control line between the w/g and c/v has failed (1), which is easy to replace with a silicone line.

[edbaus]

Wouldn't a problem with the wastegate line or the diaphram show up as overboost, not under boost.

How can I make sure that the wastegate is closing all of the way.

Thanks

Ed

[wild man]

You say you pinched off the WG line, and no difference in boost? That means either the WG is TOTALLY bad (broken off valve head, or broken spring), or you have a collapsed exhaust pipe. But I suppose it could also be a damaged turbocharger.

[nize]

1) check the vac line between the cycle valve and the wastegate using a hand vacuum pump, insure it holds pressure/vacuum and is not leaking.

this is the line you pinched off. simply disconnect it by the cycle valve (be careful you don't break the plastic nipple on the cycle valve!) and use a hand pump to check if it holds vacuum.

[wild man]

Nize is right. It could definitely be a bad WG actuator diaphragm. You might also want to check that it holds pressure, as well as vacuum. If that's not it, it could be a bent, cracked, or burned WG valve (or seat), but not likely a broken-off valve head as I mentioned in an earlier post. If that WAS the case, you would likely see near zero boost.

Just an FYI: I once over-revved my 77 924 (1st porsche, long ago) when I went to downshift from 3rd to 2nd manually (it was an automatic) at about 72mph, as I was starting to climb a mountain. I accidentally pushed the button on the shifter handle in when I downshifted, allowing it to drop into 1st gear. I knew within a fraction of a second what I had done, but by the time I got it back out of 1st, I saw the tach wind past 9500-10,000rpm! I believe it pegged. Good news was that the engine was still running, and had "some" power, but there was a definite miss to it. When I got home and let it idle, I could hear a sss-ssst, sss-ssst, kind of sound emanating from cylinder #3 (if I recall correctly). It ended up being a broken #3 exhaust valve, but fortunately, it was not broken off. The head of it looked liked a pie with 1 slice missing. I think I still have it around somewhere, if anyone wants to see a pic of it. The engine ran fine after I replaced the valve.

[edbaus]

If the line or wastegate had a leak wouldn't that show up as overboost, not underboost.

I got under the car and disconnected the line completely from the wastegate and went out and drove the car. Still the same. No extra boost.

I put the vacuum pump on the line and it held a vacuum fine.

I also loosened the 3 bolts that attach the muffler to the turbo manafold and went out and drove the car. No change (other than a bunch more noise). This was to test if the cat was clogged with something.

Now, after going out and driving the car around the block I came back and felt the wastegate pipe and it was definately warm. Not as hot as the cat pipe, but warmer than I would think that it should be if it was not opening.

My next trial would be to pull the pipe off of the exit of the wastegate to inspect the seal on the wastegate. Unless there is some way of doing this without pulling the pipe off. I fear breaking bolts.

BTW, I love having a lift.

Thanks

Ed

[944obscene]

No codes, but could it still not be computer controlled? I've noticed that my car has done this a few times to me lately. But it was inconsistent. First time, I took it home, shut it off and waited a few minutes. Turned it back on, and it boosted just fine. Second time I poked around the engine for about an hour, tripple checking vac lines etc. Nothing. No codes.

Is the car running rough sometimes? Hard cold starts or stumbling? A bad AFM reading could cause this, easy. Maybe something else too.

[nize]

Originally Posted by edbaus

If the line or wastegate had a leak wouldn't that show up as overboost, not underboost.

when the w/g line fails the car will go into failsafe mode and NOT boost. german engineers are smart, they erred on the side of caution.

thus, your test wether the w/g was opening (warm) only proves that it's failing correctly, not that it's holding boost correctly (which we already know from your previous descriptions).

try connecting a known good line to the w/g and use a hand pump to see if the w/g holds pressure/vac.

this way, if the seal has failed inside the w/g, you will know.

[edbaus]

I had a local fellow ask me to check the blow off valve. I put the mighty vac hand pump on the nipple of the blow off valve and pump it, but it would not hold a vacumm, so I guess I need one of those.

Ed

[944obscene]

Yes, I've been told that my bypass valve probably isn't holding pressure. Been driving the car for nearly a year now. I'm thinking my problem (similar in some ways) could be related to this.

[Lawrence Coppari]

Number of years ago my bypass valve (recirculating valve) went out. Result was little boost.

It's always a good idea to check the simple things first.

[edbaus]

I changed the valve and still low boost. I have plans to do some major mods to the car this winter. Still think that the WG is the real issue.

Thanks

Ed

[Techno Duck]

Ed, you can take the wastegate off and look to see if the valve is staying shut or not. More than likely you will break more than half the fasteners holding it on though, probably not worth the trouble. Seems like you tried it already, but feeling the dump tube for the wastegate with the car at idle is the best way to see if its leaking short of taking it apart. Use a IR thermometer and compare temps at the dump tube and mid-pipe.

I would add a good dual port to your list for next year, not to expensive a modification to do.

[Jkaindl]

Originally Posted by Techno Duck

Ed, you can take the wastegate off and look to see if the valve is staying shut or not. More than likely you will break more than half the fasteners holding it on though, probably not worth the trouble. Seems like you tried it already, but feeling the dump tube for the wastegate with the car at idle is the best way to see if its leaking short of taking it apart. Use a IR thermometer and compare temps at the dump tube and mid-pipe.

I would add a good dual port to your list for next year, not to expensive a modification to do.

I agree with everything Techno Duck is saying. My dual port is awesome, and he's exactly right about having fasteners breaking off the wastegate.

[nize]

Originally Posted by edbaus

I changed the valve and still low boost. I have plans to do some major mods to the car this winter. Still think that the WG is the real issue.

Thanks

Ed

ed, have you tried this test yet:
try connecting a known good line to the w/g and use a hand pump to see if the w/g holds pressure/vac.