Help, why is my engine knocking?

JimTMich · Nov 11, 2003

95 GT 99,000 miles.
Totally stock engine.
Timing set at factory 10BTDC
This thing knocks on 93 octane quality gas. I'm at 800F above sea level.
Why?
I've changed the plugs, does not help. (factory heat range)
The nocking comes and goes, like it's a gas problem, but I shouldn't have any trouble with 93 octane should I.

pardonme2711 · Nov 11, 2003

if its an automatic it might be your tourqe convertor believ it or not that can cause pinging. i had pinging and nothing worked but when i had my trans rebuilt and replaced the tourqe convertor the pinging was gone.

JimTMich · Nov 11, 2003

5 speed....
Thanks for the idea..

Joes95GT · Nov 11, 2003

Has it just started it now or has it been doing it with a few separate tanks of 93? I would first check your fuel pressure and make sure your not running too lean. If you have the fuel pressure dialed in and you still can't figure it out, I would change the ACT and ECT sensors, clean the MAF elements and change the oxygen sensors. Chances are it is one of those things.

Joe

JimTMich · Nov 11, 2003

Joes95GT said:
Has it just started it now or has it been doing it with a few separate tanks of 93? I would first check your fuel pressure and make sure your not running too lean. If you have the fuel pressure dialed in and you still can't figure it out, I would change the ACT and ECT sensors, clean the MAF elements and change the oxygen sensors. Chances are it is one of those things.

Joe

It's been doing it for 2 years, just getting worse and worse. used to be I could run 87 no problems, just got more power out of 93. For the last 2 years I need to run 93 first to keep it from nocking, now I don't know what to do. Thanks for the list! I have the stock regulator so if my pressure is off I just replace it?
I'll check the act, and ect and clean the maf with carb and choke cleaner. Ooo o2 sensors, those are fun to get at. Do those go bad without a code sometimes?

Also, it only nocks when the engine is up to temperature.
Thanks
Jim

RiceEating5.0 · Nov 11, 2003

I've got the same problem. Pings even with 93 octane. But it only does this once in a while. Especially on hot days or after a couple of good runs, or when the gas is a 1/4 full or less. I've used "sea foam" to clean out the carbon deposits, cleaned the Maf, checked the timing, and have had no luck. I think it's a fuel issue or an o2 sensor.

Joes95GT · Nov 11, 2003

JimTMich said:
It's been doing it for 2 years, just getting worse and worse. used to be I could run 87 no problems, just got more power out of 93. For the last 2 years I need to run 93 first to keep it from nocking, now I don't know what to do. Thanks for the list! I have the stock regulator so if my pressure is off I just replace it?
I'll check the act, and ect and clean the maf with carb and choke cleaner. Ooo o2 sensors, those are fun to get at. Do those go bad without a code sometimes?

Also, it only nocks when the engine is up to temperature.
Thanks
Jim

If you still have the stock regulator, I would spend the 100 bucks or however much it is and pick up an adjustable regulator. Also, have you tried retarding the timing to see when the detonation would stop?

Joe

JimTMich · Nov 11, 2003

Haven't retarted the timing, thought that if people were running 14-17 on 93 I should be able to run 10 (factory). But would be a good test.

How do you set an adjustable regulator? to factory setting with the vac hose removed and then tweek from there?
Thanks

95GTvert[bv12] · Nov 11, 2003

are your spark plugs gap correctly...also check the Fuel Pressure...it could be somthing as simple as the fuel pump

JimTMich · Nov 11, 2003

95GTvert[bv12] said:
are your spark plugs gap correctly...also check the Fuel Pressure...it could be somthing as simple as the fuel pump

Plugs are gapped at .052", checked yesterday.
Fuel pressure: I will try to figure out how to check that tonight.

Quick5pnt0 · Nov 11, 2003

If you have good fuel pressure its probably your act sensor. Most people seem to change both the act and ect at the same time because they both can contribute to knocking.
More than likely its not your fuel pressure but you never know. With efi it could be alot of things. Same goes for the 02 sensors, i doubt it but you can never tell for sure.
Mike

Rootus · Nov 11, 2003

It's also possible that you're not really at 10* BTDC. If you balancer has spun at all, the timing marks would be invalid. I'd try retarding the timing a few degrees to see if that helps any, certainly won't hurt anything.

Dave

Quick5pnt0 · Nov 11, 2003

Thats true, and you might also want to make sure you are using a quality timing light because i've heard of cheap/broken timing lights being out of range by alot!
Its just a thought
Mike

JimTMich · Nov 11, 2003

Thanks

Thanks a bunch for the experienced ideas!
I'm going to put the kids to sleep, watch Thunderball with my wife, then head out to the garage with the Hanes manual and see what I come up with.
Jim

mo_dingo · Nov 12, 2003

If it does it when the car warm's up, your ECT may be bad. Sometimes sensors degrade with time and will put out the wrong voltage.

The computer only knows if the sensor is completely dead. If it works within the specified voltage(.5V to 4.5V for the IAT sensor), the computer accepts it with no codes.

Since they are thermistors, they can degrade with time. Do a search on this forum for pinging and you will see a post from MLCstang. It gives a link on how to check your IAT/ECT sensors. I replaced my IAT sensor and that fixed my pinging problem. Doesn't need 91 octane anymore.

Getting an AFPR for your car would be a way to fix it. But you aren't really solving the problem (unless your stock FPR is bad). The adjustable ones will allow you to run rich, which eliminates pinging.
Scott

jmuva44 · Nov 12, 2003

I corrected my ping this summer by replacing the IAT sensor. Worked like a charm. Now my ping is back but I'm thinking its related to what I think is a bad harmonic balancer

JimTMich · Nov 12, 2003

Checked the resistance of the ECT and IAC thermistors and compared to the Haynes manual. The ECT looked way off, although the engine was not stone cold yet and the IAC seemed off enough that I will replace them both.

I tried to check the engine codes by watching the light on the dash instead of using the voltmeter and the codes didn't make sence.

1 3 3
1 3 3

and that was it. Haynes doesn't show anything for a 133. The first 1 was really short thought.

JimTMich · Nov 12, 2003

Replaced the parts and.....

Well, I replaced the intake air temp sensor, coolant temp sensor (both seemed pretty close to the new ones, but I replaced them any way), cleaned the MAF sensor by spraying carb cleaner on the little wires, replaced the plugs, wires, cap, rotor, and fuel filter. and while I was at the parts store I picked up a K&N air filter and put it in. Then I warmed it up and HAMMERED ON IT. 20MPH-80MPH-20-80-20-80-20-80-20-80-20-80.... got the engine nice and warm, but no knocking! of course it was sleeting out, so the cold air helps things out. I'll check it on a warmer day.

Thanks for the help guys!

I'll keep you posted

stang_gt_1994 · Nov 12, 2003

Good job.

JimTMich · Nov 13, 2003

stang_gt_1994 said:
Good job.

Thanks, we'll see, it was real strong on the way to work, but it's 28F here.

Your sig shows you added a performer intake, maf and injectors. How did those improve your setup?

Jim

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