Drmark

Hi Guys,

My 47,000 mile 95 auto GTS has been pinging under full load at between 4 and 5000 revs ever since I bought it. I have replaced the faulty knock sensors, it's fine on the Hammer check, and I run it on top grade fuel (98 ron Shell Optimax). It goes like a train and is otherwise perfect and lovingly cared for (my daily driver and 10,000 miles in the last year).
Where should I look next?
Could old plugs be hot spotting in some way ( I have taken one out and it looks fine but haven't changed them since buying the car so don't know how old they are)?
Given that it only happens under full throttle at 4-5000 in top gears (and therefore not very often given the vigilance of British cops), is it likely to harm my engine in any way?
Could it be a vacuum problem of some sort (I don't really understand this bit!)?
Any guidance would be much appreciated - as always.
Cheers
Mark

Randy V

It's common on the GTS, due to the excessive oil blow-by on this engine.

This results in a reduction of octane levels in the cylinder (due to the combustion of the oil 'diluting' the octane level of the fuel), plus carbon build-up at the top of the cylinder from the oil blow-by (further contributing to pre-detonation - pinging).

To overcome this, add a quality fuel additive on a regular basis to remove the carbon deposits. I've had real good results with the product by Liqui Moly.

Drmark

Which Liqui Moly product did you use Randy?
And is the pinging damaging?
Thanks
Mark

heinrich

I think Randy is correct. And pinging is always bad for your car.

Tom. M

You may want to check the WOT switch to make sure its telling the car to go to the wot map and add more fuel...
My GT did this...before I had my valve crash...after i put it all back together (with new knock sensor, and new WOT switch (tested bad)...the problem was gone...and yep..lots o carbon too....I'll try some of that lubromoly stuff Randy mentioned too...

Good luck,
Tom
89GT

AngelP

Mark,
You can also use a rising rate fuel pressure reg. and up the pressure a bit, if all else fails.

Angel
_________
'89 GT

Drmark

Tom,
How do I test the WOT switch?

Tom. M

There is a procedure in the manual that shows what pins to connect to on the LH brain connector...I'll see if I can dig up the reference.

Later,
Tom

P.S. I believe the spanner should have caught it..but not sure..

Drmark

Hammer / spanner test was all clear so if the WOT is included in the checks it does then the switch is OK - would be very helpful if someone could confirm either way. If it is OK I'll go with the additive alone and see what happens.
Mark

Randy V

This is the stuff:

heinrich

Thanks Randy

John Speake

>>>>>>>>>>>>>>>>>

Hi Dr Mark

You will need to run "actuator tests" (Spanner) or "input signals" Hammer to specifically test the WOT switch.

Does your GTS use much oil, especially when WOT is used ? Then as Randy says that could cause pinking.

At 47k miles the MAF should not be badly aged - this would also cause a weak mixture at WOT because you are then open loop.But it might be worth checking it to make sure.

Also running some injector cleaner might be a good idea.

Drmark

John,
Hardly uses any oil. I'm in Stroud so will speak to Paul A about testing the WOT. Will bear the MAF in mind - you're in Cambridge aren't you?
Any preferences for the injector cleaner?
Randy,
Do I have to drink it all in one go......
Thanks everyone.
Mark

Randy V

Each Sunday, mix it with orange juice and enjoy it at brunch.

1981 Shark

Randy, When you're not mixing the stuff w/OJ, where do you procure it? Some of the parts places around here, and I quote, said "Huh?!"