Questions on my boost readings - PeachParts Mercedes-Benz Forum

kartoffelpanzer · #1 09-26-2007, 12:06 PM

What's up guys-

I installed a boost gage and did some testing of the turbo yesterday. Could someone have a look at my boost figures?

1. Tach is not functioning, so references are to speedometer.
2. Gage is T-ed into the ALDA line, between the fitting on the manifold and the overboost protection valve.
3. Wastegate hose is new, hose is connected to the manifold side but has been disconnected from the wastegate side and plugged/hoseclamped with a bolt for this test
4. Overboost protection valve is new
5. ALDA has been adjusted out 1 turn CCW from previous owner's setting. Not sure if the PO tweaked the ALDA. The car seems to respond to changes in the ALDA, I went from 1/2 turn CW from the orig setting to 1 turn CCW from original setting and the increase in acceleration was noticeable. I don't think the boost figures changed though.
6. Cruising down highway, top gear, 65-70mph - boost is just under 5psi.
7. Cruising at 65-70, floor the throttle, boost creeps up to just under 10psi; I think it reached 10psi with the throttle floored and running at 80mph.

I haven't tried it on any hills yet at wide-open throttle (well, rack

) but shouldn't I be seeing higher boosts with the wastegate line plugged?

I have a dawes boost controller that I will install soon, but wanted to get this info as a reference before installing. Car seems to accelerate pretty well, but I'm unsure if it's from the blocking of the wastegate line or just the ALDA adjustments.

What do you think?

Thanks-
Rob

Monomer · #2 09-26-2007, 06:54 PM

sounds pretty good to me.

It's 8psi from factory usually (i'm not to sure on a diesel that old)

winmutt · #3 09-26-2007, 07:22 PM

Not with the waste gate hose plugged. Sounds like your flap is stuck.

kartoffelpanzer · #4 09-26-2007, 08:28 PM

Thanks for the replies. Yes, those figures from yesterday were with a plugged wastegate hose. Upstream end was attached to the turbo, downstream (wastegate) end removed from fitting in the wastegate, bolt shoved inside, hose clamp around bolt.

Boost gage is from egauges, it's the 0-15psi unit recommended on the forum. Ran it along my AC line into my cabin.

This afternoon I installed a Dawes boost controller and went back out for a drive. I ran it up a hill this time, floored in "L" and the boost never went above 9psi. Same with "S", never seems to get above 9psi.

I didn't mention it but I've already done the usual tune-up stuff:
Valves adjusted
Chain stretch is in spec
IP timing is set
New fuel filters, fuel lines
New injectors
Oil filter new
Air cleaner new
Tranny fluid and filter new
Radiator, thermostat new
Some other stuff
Currently running about 22mpg city with some highway
0-60 time is about 19-20s
ALDA 1.5 turns CCW from PO setting

Motor has about 160k on it, rest of car has 400k. I don't know if the turbocharger was replaced with the motor.

Garret turbo, haven't touched it, I've been following advice on the forums and linking in the Dawes unit into the wastegate hose.

What's the "flap"? Is this the vent to the turbo that dumps when max boost is reached? How do I test to determine if the flap's stuck open?

Sorry if my terminology is wrong, first experience with turbos here

bgkast · #5 09-26-2007, 09:24 PM

It should go much higher with the wastegate disabled. Sounds like you have the same problem I do.

ConnClark · #6 09-27-2007, 12:10 PM

You might have a worn out spring on the wastegate. It sounds like your spring is so weak that it can't keep it closed. Search the forum for instructions on adjusting your waste gate. You need to tighten up your spring even with a boost controller.

If that doesn't fix it you have a cracked valve or seat on your wastegate.

Jeremy5848 · #7 09-27-2007, 12:51 PM

I have the same 0-15 psi boost gauge as you, connected directly to a spare port in the intake manifold of my 1985 car. I can "see" the wastegate open by watching the gauge. The boost builds up to about 11 psi and then drops back a little when the wastegate pops open. It recovers a bit and stays around 10 psi.

I discovered a few months ago that the flex pipe from the trap cat (or exhaust manifold in the case of a non-CA '85 diesel) to the EGR valve was cracked in half and leaking. The leak was enough to rob the turbo of a surprising amount of its drive. Once the leak was fixed, I found that the boost built up much faster, although ultimately it didn't get any higher.

Other than that possibility, I agree with the posters who advise checking the spring that holds the wastegate closed.

Jeremy

kartoffelpanzer · #8 09-27-2007, 05:29 PM

That's good advice. Doesn't the pressure of the exhaust force the wastegate shut, though? I hadn't even thought about the fact that the wastegate spring may simply not even be stiff enough to hold the gate closed.

Jeremy - I don't get that peak-back off behavior so I suppose that's another pointer to the wastegate. I don't have EGR though...so I suppose one less thing to worry about in troubleshooting this.

I'll give the spring adjustment a try, will do 3 full turns CW of the adjusting nut per the DIY instructions unless there are other recommendations.

Last night I bypassed the overboost protection solenoid to see if anything there was contributory but I get the same performance, can't seem to get above 8-9 psi.

Could there be other issues causing this? From what I understand about boost needing more fuel to raise boost, it could be fuel that's limiting the boost. When I first worked with my ALDA I read threads that said open the ALDA until you see whisps of smoke on hard acceleration, daytime...I remember at one point I opened the ALDA all the way expecting to see big smoke and didn't see much of anything. The vehicle does seem to accelerate more quickly as the ALDA is opened, though.

Thanks again for the advice, will update when I get something.