Not getting full boost at WOT

[newsh]

I mentioned last week that my car was giving less than full boost, only a max of 20psi and falling off rapidly instead of about 26 and holding.
Well I have a further suss on this tonight as I noticed at one point that as I backed off the throttle slightly the boost popped up to the normal 26psi and the car took off. I then did some experiments, trying to drive at less than full throttle which is actually quite difficult.. No don't laugh.. I mean its easy to drive at 1/4 or 1/2 throttle but not easy to drive at 95%. If I do drive at just below full throttle though the car makes a good 26psi of boost as per the MRC remap, holds it as it should and goes like a rocket.
So now I'm wondering why, seems to me it must be something to do with the TPS? I had thought that it was a boost leak with pressure escaping at full throttle, though I'd be surprised if it is now.
Maybe the TPS is going past its end stop and not giving the WOT signal when the pedal is at the floor? Is this even possible?
Any ideas lads?
I still havent had any time to take a good look at the car but should get some time on Sunday all being well and I'd like to get it sorted out now

[ericd]

worth checking the throttle cable is adjusted correctly and not slipping at WOT, we've see a few problems with cables sticking, not fully releasing or badly adjusted even on cars that seemed to generally running ok , but were never getting to WOT.

John , I'm guessing when the head was off all the related throttle assembly was off and reconnected etc, might just need tweaked...

[T2Andy]

I noticed this tonight ,after comming off WOT the car surged at about 95% throttle like you said .Ithought it might be getting to much fuel .

[newsh]

Throttle cable is definitely going tight when the pedal is on the floor, I did manage to check this with a mate pushing the pedal for me. Is this right though? Maybe its too tight? Since I used a spacer on the throttle body for the RS2 IM the inner cable is actually a bit short, I have some spacers I made to compensate but need the longer bolts too, I might try loosening the cable and see what happens. Really I need to find out if the TPS is working correctly.

[s2dude]

Throttle cable is definitely going tight when the pedal is on the floor, I did manage to check this with a mate pushing the pedal for me. Is this right though? Maybe its too tight? Since I used a spacer on the throttle body for the RS2 IM the inner cable is actually a bit short, I have some spacers I made to compensate but need the longer bolts too, I might try loosening the cable and see what happens. Really I need to find out if the TPS is working correctly.

When I first bought the S2 someone tensioned my throttle cable up totally using the metal clip for adjustment so the cable was tense on no throttle....(trying to be helpful)

A year nearly later and the Throttle body linkage snapped (the plastic lock/guide piece at the end of the cable) causing me to lose all power on the fast lane of the M1

I later found out it only needs to be "just tight enough" to open the throttle fully with an assistant doing the peddle and you testing.

I dont think this would account for your lack of full boost at WOT but is worth bearing in mind and possibly using a longer throttle cable...or thinner spacer so it does not have to be taught all the time.
hth

[newsh]

Thanks for replies, I've just fitted some spacers to the Cable perch so the cable doesn't go dead tight at WOT, hasn't fixed it so need to space some more to get reliable boost, but this is surely just symptomatic. I gave the whole thing a good pressure test and there's no boost leaks.
I've tested the TPS and it gives
2k ohms across 1 and 2 does not change as you open throttle.
0.9k rising to 2.7k across 1 and 3
2.7k falling to 0.9k across 2 and 3
So it seems to be functional although the high reading on S2 Central is 3.6k Ohms..

It really is that last 1/2 an inch push on the throttle that kills the boost, I just dont get it..

[newsh]

Another 5mm of spacer on the throttle perch and I can now floor it and get decent boost, this car goes when its right.

I can only think that there's some sort of problem between the WOT value of the TPS and the boost map, perhaps it has changed since it was mapped. I need to get it booked in to MRC for a full check up I think.

[newsh]

Spacers

[Greg_S]

Throttle cable looks fine, have you tried pulling the fault codes off?

[newsh]

Hi Greg, no, I havent pulled the codes, will have a go with the LED in the morning. I did speak to Doug and book the car in though

Incidentally I tried disconnecting the TPS and it just reverted to 1 bar boost (spring only) and the idle was crap.

Throttle cable looks fine, have you tried pulling the fault codes off?

[jalmarsfar]

Whats this for?


I have unscrewed that one and i cant find any info on how it should sit. Any ideas?