Cats Causing Spark Knock?

[Frank.Rizzo]

Hello!

I just recently bought a 5-speed, 1994 Ford Mustang GT that I found in great condition. It has 120K miles and is 100% stock. The only problem I noticed was that it was pinging under acceleration when I test drove it. I thought that maybe the owner (an older woman) was using regular unleaded gas or it just needed a tune-up. Immediately after buying it, I took it to a local Mustang shop. They performed a tune up, replacing the spark plugs, spark plug wires, distributor cap and rotor with all Ford Racing parts.

Unfortunately, the car still pings, even though I use super-unleaded (91 Octane in Southern California) and have tried different gas stations. If it is cold, it won’t ping until about 3200 RPM’s. If it’s a warm day, or if the car has been in traffic, or if the A/C is on, it constantly pings starting at about 2400RPM, under acceleration.

The local mustang shop is saying my catalytic converters may be to blame because they are original and may be getting “plugged up” so they suggest getting an after-market exhaust with new catalytic converters. I plan to replace the exhaust in the future, but don’t want to do it before I have done some research and found the headers and exhaust set-up that I want. In the meantime, could the pinging be something else?

I saw the post about trying Autolite 24's gapped @ .060-.061 and I will check into that, but any other hints would be appreciated.

Thanks for the help!

 

[mo_dingo]

There are a lot of things that can make your car ping. It seems like our cars get it worse than others.

Test your MAF/IAT sensors (mass air flow, intake air temp.) The IAT sensor is also called a ACT (air charge temp). Do a search on this board for "Pinging Gone". It was a write-up written by MLC Stang and will tell you how to test the MAF/IAT.

Test your TPS sensor. Again, do a search on this board.

Do a detailed inspection of all vacuum lines. The tiniest crack can cause a lean condition. Remove each line one at a time, and inspect them (be anal about any crack).

Remove the spark plugs, and check their condition. They should have a little white tinge to them because of the pinging.

When your motor is cold, start the car, run it at appx. 1500 rpm's, and spray an entire can of carb cleaner into the intake manifold. (remove the rubber intake hose and spray into the throttle body)

Repeat the carb cleaner process ONCE more if the first time did nothing.

That should get all of the carbon deposits out of the engine. But remember to do it while the car is bone cold, so the carb cleaner doesn't atomize as much at the intake manifold.

How does the car run at idle? Are the rpm's stable? Does it run rough?

If you idle is rough/low speed, try cleaning your IAC (idle air control)valve. You should do it anyway, but it might be a problem.
Scott

 

[1fstgt]

there are hundreds of things that could make it ping. the first thing i'd check would be the timing. it's a shot in the dark since a old lady owned it but it could be advanced a little too far.

 

[cjones]

as stated above: check the timing, check/clean the MAF.

what you are descibing are classic signs of a bad MAF.

cats will not cause your car to ping.

if you are in orange county check out www.x-m-p.com they can check out the car for you.