pitten

Hello fellows,
been lurking this forum for quite some time now and the day has come that I can't find answers by searching anymore.
A week ago I was giving my 89 200 TQ w/ IA chip/spring some fire and something went wrong. Since then it revs up slower then it used to and doesn't go higher then about 4-5k. I just redid all injectors including seats, shrouds and O-rings, put in a new throttle switch, checked intake tubing for leaks and turbo for free movement. Long story short, I couldn't find anything, and it turns out that after all this wrenching and replacing I didn't fix anything either. It appears to run a little smoother with the new injectors, but the rev limitation and zero-boost condition persists. The only thing I did notice afterwards was the MM-hose between IC and TB collapsing when opening the throttle fast or more than 2/3, like something before it in the plumbing would be heavily clogged. I've read of intercoolers bursting under the increased boost, but that wouldn't result in a restriction would it? And I didn't see any obvious signs of intercooler leakage either. Unfortunately I haven't had the chance yet to check if my turbo actually delivers compressed air.
All in all I'm quite confused and would appreciate any input on this.
Thanks, Pit

boxerfan

Remember you will only build boost under load. You can't rev oin the driveway and see any boost... EVER.

OK, that said, a collapsing hose certainly sounds like it needs to be replaced. At idle you should see vac. and after a rev when the throttle plate closes even more vac.... but that should be behind the throttle plate. It is common for an old MM hose to rip. they often allow the car to idle but as soon as you try and build any boost pressure the rip opens and all the boost just flows out.

A really big vac leak will make the car hard to start. All the tubing from the intake should be considered suspect. Check each and every hose on the manifold.

There are ways to pressure test the intake system. Try that. Search the forum and you will find it explained. It is good to use smoke to help spot the leaks.

Kneale Brownson

Sounds like you've got some sort of restriction. Maybe the cat is plugged?

pitten

thanks for the response guys, I know I need load for the turbo to actually boost, I might not have mentioned it but I actually drove the car in that state, just noticed the collapsing hose in the driveway. Since I have my analog boost gauge connected to the intake manifold, after the throttle body, it verifies at least that there's no pressure reaching the IM. I will of course try to conduct a serious pressure and flow test, but the MM hose is literally collapsing, like what your straw does when the milkshake is too thick, how could that be caused by a clogged cat?! The starting behavior actually got a little better after the injector job, as it should, but of course it's very naive to rule out vacuum leaks on an MC2. I'll try to work my way "back" from the TB and see what I can find. Thanks so far!

Kneale Brownson

I was thinking of common problems like the cat internals failing and clogging the exhaust, which can limit power.

Maybe a mouse crawled into the plumbing ahead of the intercooler?

pitten

LOL, that's quite funny Kneale, but I'd consider that highly unlikely ..I also thought about something being sucked in there, but where the heck could it come from? I just checked my air filter a couple weeks ago and it wasn't even dirty enough to replace it at that time, so I would be very surprised if it clogged up that heavy since then. Plus it appeared to be a sudden change, somewhere in 3rd or 4th gear at WOT. Could the fuel metering plate be the culprit? It seems it just can't breathe enough to rev high or accelerate fast.

Kneale Brownson

My thought is the MM hose collapsing indicates the intake suction is great (plenty of fuel to make the engine run) but something is keeping the MM hose from getting air to feed that suction.

BTW, did you take the filter out of the box or just look at how clean it was on top?

pitten

we're on the same page there I see, something in the system before the MM hose has to restrict air flow heavily..the hose collapsing is another indicator for me that at least that hose is not torn, since then it would just suck in unmetered air rather than collapse..but I have to admit I only checked the air filter from the outside, didn't take it out since that's quite a PITA IMHO..I'll try to check for restricting mice asap thanks for bearing with me here

Kneale Brownson

I once found nesting material and a lot of acorns beneath the air cleaner. Maybe something got sucked up against the screen into the MAF.

boxerfan

Is it old? Is it correct?

If there was enough blockage to collapse the MM hose I would think that starting and idle would be greatly affected.

The real hint in what I read was that this started to happen at a WOT spirited drive. That equals boost leak to me. When you shift the throttle plate closes and sends a shock wave back through the incomming column of air. You can easily blow the end caps off the intercooler (BTDT), pop hoses of any description attached to the pressurized intake (BTDT too).

Either way. To find a blockage you suspect you'll need to remove and clean your plumbing so have at her. Check them all.