zakk

Ok, I picked up my 86 951 (first one!) wednesday night (at a good price, too). On the 300 mile drive home, there was one instance where I was in 5th and went WOT to pass and the car lost power, felt like a rev limiter type power loss. So I backed off and tried it again, and it didn't quite do the same thing, it bucked once or twice this time. It's happened a few times since then, always at high boost. I've also noticed it doesn't have to be at WOT, just high boost. It seems to occur just after starting the car (the 5th gear one was right after we stopped at a rest area). So the current theories are:

• previous owner suspects the wastegate was shimmed. Possibly an overboost situation?
• vacuum leak somewhere
• TPS issue
• Fuel delivery issue. possibly dirty filter
  

I plan on doing some poking around tomorrow. Any possible culprits I've missed here? Hints on where to start first. I should add the car idles pretty smooth, at about 1k. A bit high, so I'll be adjusting that down also.

Danno

"It's happened a few times since then, always at high boost."

What boost levels are you hitting when this stumbling occurs?

Sounds like you're hitting the overboost protection which is built into the computers to protect the engine. You don't even have to have aftermarket upgrades to have this occur. If any of the vacuum lines leading to your turbo has a leak, this will increase your boost unexpectantly and hit the overboost protection. This limit is actually different depending upon RPM.

BoostGuy951

I had this happen to me.

My battery terminals were rocking back and bridging on the hood. Make sure your hold-down is secure and you have terminal covers.

zakk

[quote]Originally posted by Danno:
<strong>"It's happened a few times since then, always at high boost."

What boost levels are you hitting when this stumbling occurs?

</strong><hr></blockquote>

The stock boost gauge is pegged to the right when it happens. I have a boost gauge on order right now so I can get some better data there.

My initial suspicion was that the wastegate was shimmed, but it's still running on stock chips. A bit more research has led me to lean more towards a leak somewhere. I just dug through the service records I do have, and there is a mention "leak at wastegate tube" on a pre-purchase inspection. No mention of it being addressed, so it's a starting point for tomorrow, at least.

special tool

That'll do it, especially with a shimmed wastegate. See if you can post pics of the shims, to see if someone didn't get carried away.

jimbo1111

To me it sound like your wastegate is bleeding off due to a weak spring.

zakk

Alright, I didn't get a chance to get under the car today, but I did some other poking around. I noticed it was low on oil, so I added some (2.5 quarts, eek) and took the car out. It happened once while I was out, driving it pretty hard. However, it did confirm one of my suspicions. It only occurs when the car is cold. Once the car warms up it doesn't seem to happen no matter how hard I hit the boost. I plan on taking the next daylight opportunity to get under the car and check the connections to the wastegate and turbo, but the only occuring while cold part has me stumped.

adrial

My car had a similar problem before...though mine was more of a stumble, then more acceleration when it was mild.

I think the situation got worse and worse until eventually the car would barely go anywhere...boost or no boost.

I cant remember what the solution was though...either fuel filter or AFM (air flow meter)...or maybe it just resolved itself...?

wasteg8

zakk--check the clamps on your intake hoses. I experienced the same thing at w-o-t ..turned out I had a hose clamp broken allowing the hoses to deform and suck air at max boost. simple fix for what seemed like a MAJOR problem. hope this helps!

zakk

Ok, another data point. If I get it to do the bucking/power loss and have to stop soon after, it will consistently stall when I start again. Starts
right back up. It didn't do this before I topped off
the oil. Now I'm just confused...

jimbo1111

i think danno may be rite . your hitting over boost protection. If you have chips then you don't have overboost protection but your knock sensor is detecting knock and retarding timing. when you reset the ignition the timing gose back to normal. your over boosting for sure. check your hoses to your wastegate for cracks and leaks, don't drive you car like that for to long you will blow the motor.

dmoffitt

I had this. first time it was a blown hose (turbo to intercooler, the rubber part @ the IC).

second time, turned out the line from the banjo-bolt on the IC pipe that goes to the wastegate had literally torn itself in half (ie, the wastegate WASN'T opening at all, i hit something stupid like 24+psi and then the overboost protection kicked in and it was like hitting a brick wall. god was she ever pulling HARD before that tho

good luck, i'm STILL chasing down vac. leaks and such.... one of the small prices to pay to own such a fun car overall <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

zakk

Ok, just went and started looking around for loose hoses, clamps, etc. And I found something! Just want to ask what exactly I found and verify I won't blow anything up if I fix it: what is this?

Clearly something isn't connected correctly there. Is there a hose clamp I need to get to properly attach that, or will pushing it back on with sufficient force work? Maybe as I learn all this stuff I'll produce a newbie's map to 'what part is what in your engine'!

sm

If you're talking about the brass cylinder, that's the fuel dampner. The rubble "T" should be simply pushed on to the nipple of the fuel dampner. I hope that solves your problem!