Lumpy boost?

[speedypancake]

After failing to drill out a broken manifold stud, I've put her ('96 Aero) back together again to drive to the garage. However, the noise is so much better now I'm considering just fitting a new manifold gasket (currently running without one) until we can better afford to get the 2 studs fixed properly.

But I'm now having boost problems

With the APC electrically disconnected, I do seem to get base boost, and it seems fairly smooth. However, with the APC working, if I floor it, the boost is "lumpy" or not smooth, then it shoots up well past the red and then the inevitable fuel cutoff bump.

Does anyone think this could be related to running without a manifold gasket and an old manifold / turbo gasket?

So far I've checked the hoses & tried cleaning out the APC with carb cleaner (no difference). Also swapped the DI cartridge for my spare and again no difference...

[speedypancake]

At the risk of talking to myself..

Finally managed to cure my lumpy acceleration today. All it needed was a new set of spark plugs

The plugs that came out must have been a year / 18,000 miles old. They were all white (lean?) and worn so the gap looked more like 2 or 3mm than the recommended 1mm. I guess with all the problems I've been having recently, I just assumed the boost problems were down to leaking / missing manifold gasket etc. Just one final question - the local autobits supplied me with NGK BCPR6ES but it had BCPR7ES in there already?

Whatever - Now back to full warp factor

[mark e]

You need to change the plugs. The 6s are too hot. You will get problems with knock-induced boost retard. 7s are the correct ones.

[speedypancake]

You need to change the plugs. The 6s are too hot. You will get problems with knock-induced boost retard. 7s are the correct ones.[/b]

Thanks for that - I'll change them later today
So good to have my boost back

[Paul D]

The plugs that came out must have been a year / 18,000 miles old. They were all white (lean?) and worn so the gap looked more like 2 or 3mm than the recommended 1mm.[/b]

Yes - white plugs indicate mixture too lean. Ideally they should be light brown colour.
I find after 10k miles the plug gap only reaches 1.2mm. If yours were 2mm, then they must either have been set wrong in the first place, or not changed for well over 20k miles - which means the car should be fully services ASAP - on the reasonable assumption that if the plugs haven't been checked in 20k++ miles, then the oil + filters etc may not have been changed either.

When you buy NGK BCPR7ES-11 (with the 11 suffix) they will be pre-gapped to 1.1mm. Run these for a couple of tanks of fuel and recheck plug colour. If still too lean, you may need a a modification to the fueling program, via the ECU.

[speedypancake]

Thanks Paul.

I've now fitted the correct plugs and everything looks OK. I'll keep an eye on the colour as you suggested.
Also got new engine oil and will change at the first opportunity.

Cheers