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Toyota MR2 (Turbo) Import - Flat spot under acceleration - Fixed #

Posted by Pete Mutlow on June 3, 2009, 10:46 pm

Year of Manufacture *: 1990
Engine Code or Type *: 3S - GTE 2.0L
( Optional ) ECU Type: TCCS
( Optional ) Scanner used: ACR4 G2

Evening all;

This vehicle has a severe flat spot under acceleration and if accelerator is blipped quickly will stall on return to idle. No flat-spot is evident when conducting this test in neutral. The engine management system includes a moving flap AFM with adjustable mixture air bleed screw, a single wire o2 sensor and MAP sensor. I believe the MAP sensor is there for the Turbo. I have adjusted the mixture by turning the mixture bleed screw until the o2 sensor can "cope" with it and start switching in the normal fashion in an acceptable manner. CO is approx 1.4%, HC is 120ppm, CO2 is about12.6% and o2 a little high at about 2.6% (twin big bore exhausts). At fast idle, the CO is a bit high at about 3.6%. I believe there is an AFM issue but for some reason will not pico-scope. On a digital multi-meter we have 2.5v at idle and dropping to about 1v at fast idle. I would expect to see the opposite but rising to 4.5v at fast idle. On inspection the moving flap is free in movement but appears to be mis-aligned. Are these findings just peculiar to the TCCS system or do I fork out for another AFM?
Would value your thoughts.

Regards

Pete M

Re: Toyota MR2 (Turbo) Import - Flat spot under acceleration #

Posted by brian cowan <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT5585' width='330' height='300' border=0 style='border:none;'> on June 4, 2009, 9:19 pm, in reply to "Toyota MR2 (Turbo) Import - Flat spot under acceleration #"
Brian Cowan

Hi Pete, I think afm voltage starts high then reduces the higher air flow. I had one in this week that didn't run hardly, turned out to be intercooler pipe popped off and dramatically affected afm output. Is it possible you have a similar issue but not as severe (small leak). hth brian

Re: Toyota MR2 (Turbo) Import - Flat spot under acceleration #

Posted by Pete Mutlow <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1569' width='330' height='300' border=0 style='border:none;'> on June 4, 2009, 10:49 pm, in reply to "Re: Toyota MR2 (Turbo) Import - Flat spot under acceleration #"
Peter Mutlow

Thanks for that Brian, will get the garage to check that one out. Cannot find what the voltages should be on the AFM - any info would be useful. Incidently I don't think the flap can be mis-aligned otherwise it would be sticking. However, the gap is not uniform along the edge of the flap. Perhaps a vacuum check might produce something. Incidently, the cat has been removed - hence the open loop emission readings.

Regards

Pete M

Re: Toyota MR2 (Turbo) Import - Flat spot under acceleration #

Posted by Pete Mutlow <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1569' width='330' height='300' border=0 style='border:none;'> on June 17, 2009, 10:50 pm, in reply to "Re: Toyota MR2 (Turbo) Import - Flat spot under acceleration #"
Peter Mutlow

Evening all,

Inter-cooler pipe checked and OK. AFM fitted (Flap symetrical - unlike original) and fault still there. Did Vac check and was low at 15"hg and dropping off rapidly at high revs a la blocked exhaust, Exhaust had already been dismantled and checked for blockages. So assuming exhaust is OK and engine appears ok (hydraulic tappets) with compressions at approx 180 psi, attention now turning to intake system or specifically the turbo set up. My knowledge on turbos is poor and I wonder if there is anything on the turbo system that can cause this problem.

Regards

Pete M

Re: Toyota MR2 (Turbo) Import - Flat spot under acceleration #

Posted by Paul Foster <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT2680' width='330' height='300' border=0 style='border:none;'> on June 22, 2009, 10:52 am, in reply to "Re: Toyota MR2 (Turbo) Import - Flat spot under acceleration #"
Paul Foster

Hi.

Please correct me if I'm wrong but surely the vac will drop as the rpm is raised as the turbo starts to pressurise.

-15"hg is a bit too low at idle though - Daft question - Is it possible that the valve timing could be out by a tooth?

Just my thoughts - Paul.

Ne te confundant illegitimi

Re: Toyota MR2 (Turbo) Import - Flat spot under acceleration #

Posted by Pete Mutlow <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1569' width='330' height='300' border=0 style='border:none;'> on June 22, 2009, 12:53 pm, in reply to "Re: Toyota MR2 (Turbo) Import - Flat spot under acceleration #"
Peter Mutlow

Hi Paul,

I was completely unaware that vac reading will drop when turbo pressurizes. I understand the initial drop on throttle opening but thought turbos would react in the same manner as a normal aspirated engine. ie vac reading would recover to 19-21"hg. Something new learnt today. Yes, 15" is low but garage assures me that cam timing has been checked. Customer has vehicle back whilst we figure out where to go next.

Regards

Pete M

Fixed #

Posted by Pete Mutlow on December 12, 2009, 7:04 pm, in reply to "Re: Toyota MR2 (Turbo) Import - Flat spot under acceleration #"
Message modified by board administrator December 14, 2009, 11:48 am

Evening,

This was fixed on a friends rolling road. Would never play up whilst in my care and waiting for fault to materialise. Vehicle run hard on rolling road (with engine cover closed) and fault quickly appeared. After various attempts at this, fault was found to be a LT wire to distributor which was found to be making and breaking contact. Now, I have no idea how this would be the cause, but I have posted it nonetheless.

Regards

Pete M

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