94 855 turbo problem

[edwingsiu]

I have a 94 855 turbo. when the rpm hit around 3000 to 4000, it seems don't want to go any higher and engine sounds like one of the cylinder not working and the rpm will raise very slow as well as the speed. I also notice the idle is not stable when at red light (not noticeable by looking at the rpm but I can feel the jerk). It is more noticeable when a/c is on. Everything had been check incl leak, plugs and so on but nothing found. Fuel filter has been changed and throttle body has been clean. My mechanic suggests it could be a plug cat. It all happen after I shorten the wastegate and even restore it to the orig setting doesn't change except the problem might delay to 4000 rpm. Other than that the car has lots of power and derives very smooth if I take it easy and keep running in low rpm. I have search all the forum I know and noone seems to have this problem. Also this is very hard for me to explain, hope you guys understand what I am trying to say. Thanks.

[Bracer]

Hello

And



Nice to see you could make it.

[Bracer]

Right this still sound like "Overboost".

I would be inclined to advise you to go and take a few more turns of the Waste Gate Actuator, it sound like you could have disturbed something when you increased the pre-tension.

But I do have a few question which will help me further.

1) What did your stock boost gauge go up to before you adjusted the W/G ?

2) Did the fault appear straight after you made the adjustment ?

3) How many turns of adjustment did you make ?

4) What does your boost gauge show currently ?

That will do for now, if you could answer those please then we can go from there

[edwingsiu]

Thanks Steve. Pls see answer below

I would be inclined to advise you to go and take a few more turns of the Waste Gate Actuator, it sound like you could have disturbed something when you increased the pre-tension.
edwingsiu reply: I have lose the tension to max and the only different is the problem comes back at higher rpm instead of 3000.


But I do have a few question which will help me further.

1) What did your stock boost gauge go up to before you adjusted the W/G ?
edwingsiu reply: not sure since i had a hose leak and i think it was about 1/4 or less over the white.

2) Did the fault appear straight after you made the adjustment ?
Edwingsiu reply: no it did not. that's why i have a feeling it was not cause by the adjustment except if i ever bended the rod.

3) How many turns of adjustment did you make ?
edwingsiu reply: since i have forgot the orig setting. I have decide to turn it to the point where i can drop it to the pin and assume it was base. I used the football pump and pump it to about 6 psi (which was suggested by someone i forgot who and where that I can set it between 6 to 8 psi) and it works out to about 12 turns from where I so call base setting. and the result was great.

4) What does your boost gauge show currently ?
edwingsiu reply: If I floor it, it will go as high as 3/4 of the white. otherwise, it will run at around 1/4 of the white at about 2500 to 3000 rpm. If I adj the rod to base, it will run at around 1/4 of the white at 3000 rpm.

Everything is pretty well stock on my car. The only thing i did was the wastegate and holes in the air box. Since I don't want to spend too much money on performance stuffs and where I live don't have too many motorway, I smooth and low end power can make me happy. that's why i just want to do a little trick in the econ way.

Hope this is enough infor for you. thanks.

[Bracer]

Hmmmm

Right sound like you could have a bad vac leak.

From stock the boost gauge should reach 3/4 into the white area. Which is around the 9 psi stock boost level, the end of the white area is around 14.5 (1.0 Bar) and this is also the level at which the stock ECU will cut the ignition in the event of "Overboost".

So to start with your car wasn't right or your gauge had a major leak ?

Now you estimated 12 turns on the WG this is way out. Most end up with 2 or 4 and some 6 but 12 we have another problem.

Now trying to sort this in my head I keep thinking, your WG is now too loose and cant build boost and the turbo could be going into overspin, and secondly you have a bad vac leak.

Have another quick look at your pipes and see if you can find anything obvious. Also check the connections to the BCS and if you get the chance pop down to a garage that can hook up a calibrated boost gauge, if you dont want to invest in one, but if your playing with boost for £25 they are well worth it and could save your rods, which by the way I dont believe you've bent as you would have mentioned a major ticking sound over and above that of the injectors and the idle control valve.

I'm sure this is just somthing silly and am confident now its a vac leak.

Steve

[fireplums]

did i see a link somewhere to a post on how and what to check for air leaks?

[edwingsiu]

Finaly my car is fix. Now I can have constant boost at 10psi and spike at 14. Is it what it should be? Anyways, it was the spark plug. I was using the NGK spark plug (forgot what it was.) It was recommanded by someone at the forum (forgot which forum though) When I inspect the gapping, it was far apart and I think it was 1.1 vs factory 0.7 I ended up replace them with Bosh platinum and now she is pulling strong. I wonder if I really did put in a wrong plug since I didn't have any problem when I replaced them or I screw up the plug when I was playing with the wastgate and boost was too high and screw up the plug?
Do the gapping go futher apart when they are wear out?