94 GT pinging, help please

Canary94GT · Aug 29, 2011

My 94 GT with 81500 original miles has been pinging for a few years now, or about 3000-5000 miles. It's stock minus a JLT cold air intake and a flowmaster cat-back exhaust.

When I first began driving it about 4 years ago, I did not notice it at all, so it appeared to begin happening suddenly.

The pinging occurs at nearly any rpm if the engine is under load. It will happen from 800+ rpm when I get going on flat ground in 1st gear. I don't hear pinging when I'm cruising at a steady speed on flat ground. It will also ping regardless if it's 40 degrees out or 90 degrees out.

I have aggressively searched google and tried several things to fix it, including:

- Running 89 octane currently (running 91 doesn't seem to help any.. also note: contains up to 10% ethanol)
- Had shop replace broken EGR system (so it is supposedly fixed, it was broken)
- Replaced fuel filter <3000 miles ago
- Cleaned MAF sensor with MAF cleaner
- Replaced ACT sensor
- Replaced ECT sensor (was getting CEL code 116)
- Changed platinum autolite 25 plugs to copper autolite 24's (one step colder) and gapped them correctly (were gapped incorrectly at .042 rather than .052)
- Replaced cap and rotor (wires are relatively new)
- Ran a couple rounds of seafoam through a vacuum line (didn't get much smoke)
- Retarded timing from 8* to 6* (didn't seem to do anything really)
- Checked and found balancer is NOT spun
- Checked fuel pressure, is 32 psi w/ vacuum and 40 psi w/o vacuum
Since I started this thread:
- Replaced PCV valve and PCV filter (was really gunked up)
- Reinstalled factory air cleaner to see if the CAI was causing issues. The switch didn't change the pinging.
- Tried 89-octane ethanol-fee gas (assuming the station still sells ethanol-free), and noticed little to no difference
- Changed o2 sensors - might be noticing some improvement. Only took for a short drive and maybe it takes some time for the computer to adjust to them?

The last mechanic that I went to (who replaced the EGR system) said it could not be fixed because of the ethanol that is put in gas these days. However, I will not take "no" as an answer - I believe it can be fixed.

Does anyone have any ideas on what is causing it? If more elaboration is needed on my part, I'd gladly do so.

99FiveOh · Aug 29, 2011

Mechanics these days = View attachment 184257

However, it looks like you've covered all your bases here. Have you by chance ever replaced the distributor on that car?

Canary94GT · Aug 29, 2011

I agree about the mechanics... I fret to even take it to them anymore due to them not knowing what they're doing, then charging me up the ass for it.

I have not replaced the distributor - hasn't been removed to my knowledge.

Zero Signal · Aug 30, 2011

Have you tried rotating the MAF sensor around to different angles? Sometimes a new intake messes with the flow across the thermistor element in the MAF sensor. Just guessing here. . .

I would test the EGR system yourself. I wouldn't trust the mechanic unless you know he's good. I have a pinging problem right now and I think the vacuum solenoid in the fender might be bad because the EGR valve itself actuates just fine with vacuum applied.

You checked the fuel pressure, but did you check the hold pressure? Make sure the FPR is still good, even though there is pressure while it's running. 40psi sounds low to me.

Lastly, it might be worth picking up some rebuilt injectors on ebay for $70. The newer/better 4-hole plate type.

Also, how about the O2 sensors? How old are they?

Canary94GT · Aug 30, 2011

Thank you for all the ideas.

I plan to either rotate the MAF sensor or try the stock air box again to see if that eliminates the problem, but I think the pinging started before the CAI - I can't remember.

Also, I did check the hold pressure and it was 35-40 psi.

The o2 sensors are original I believe. When I was doing this research on google, I came across information saying that if it is pinging under part throttle but not WOT, it might be the o2 sensors causing it. But I'm not really sure if it pings at WOT cause I haven't really floored it since this began happening. That's what you have to do, right? Put the gas to the floor?

As I mentioned above, I get bad pinging at low rpms but it seems to lessen at higher rpms. Haven't really noticed if gas pedal position affects it, but I will have to test.

I haven't received any o2 sensor-related check engine codes, but I understand they can malfunction without throwing codes.

WhiteCobra95 · Aug 30, 2011

Have you checked the PCV system? Oil in the intake from a stuck open PCV valve will lower your knock threshold, and since your still knocking with higher octane fuel and low air temps oil contamination sounds very plausible. (Oil in a gasoline combustion chamber is like diesel fuel.) It doesn't take much oil flow to do this, and sometimes you barely see or smell it in the exhaust. Is she consuming any oil?

The PCV valve at the back of the intake manifold is the spot to check. A higher mileage engine with some blow-by will push oil into the intake manifold under load if that valve is stuck open. You could try replacing the PCV valve ($3) and see if it goes away, or pull the upper intake and look for wet oil on the walls to confirm the problem. (I think there's also a mesh below the valve to help separate oil if you want to replace that at the same time.) You can also just pull the PCV valve out to see if's stuck open, but sometimes they close up when you rattle them around to get that stubborn hose off of the valve.

The E10 excuse the mechanic is using is not true. If anything, the ethanol content will make you less knock sensitive. E10 does have a lower stoich than E0/gasoline, but if your O2's/closed loop control is working properly it will adapt the fuel trim to the fuel type and offset the stoich/AFR shift by increasing the pulse width. E10 is not the problem.

Canary94GT · Aug 30, 2011

Not sure when the PCV valve was last replaced, I thought a mechanic did it recently but can't remember.

Motor is hot right now after a drive, so I will have to wait for it to cool off a bit.

But I have noticed oil in the tube coming from the oil filler cap neck into the intake. It doesn't appear to be a whole bunch, but enough for a light coating on the inside of the intake after a few thousand miles. Is there any way to prevent this, or is it normal?

Also, I just tried rotating the MAF sensor and it didn't appear to help.

Really tempted to replace the o2 sensors, but my wallet is hurting from throwing all these parts at it.

Canary94GT · Aug 30, 2011

Okay, just pulled the pcv valve out, the grommet came with it. The PCV valve seems to be rattling, but is oily inside and I haven't been able to get it off the hose yet. I took a flashlight and looked down at the PCV filter and it looks pretty clogged with oil. Unfortunately I am unable to move it with a screwdriver.

Is this bad news that oil was getting in there and that's it's clogged, or is that expected at 80k miles?

Doesn't a clogged pcv system allow oil into the air cleaner housing as I noticed?

Adam95GT · Aug 30, 2011

Nevermind.

Canary94GT · Aug 30, 2011

Went out and bought the new pcv valve filter and pcv valve. The old filter was really jammed in the intake, so I took a 2" screw and screwed it into the filter and took some pliers and yanked like hell.

My first attempt only removed the screen on the filter, then i screwed it in further and finally with tons of yanking it popped out.

Man is it caked with oil. Regardless if this fixes my pinging problem or not, this needed to be replaced.

Thank you WhiteCobra95 for bringing it to my attention.

99FiveOh · Aug 30, 2011

Adam95GT said:
Nevermind.

I don't see an edited post, so what's with the nevermind?

And to the OP, yes that screen was nasty, needed to be replaced for sure! I have found that sometimes problems with these cars aren't due to one problem but a combination of little things here and there. If you can't figure it out right away then it's ok to replace things that ought to be replaced anyway.

Canary94GT · Aug 30, 2011

NotA4.6, if you edit your post within a minute or two, it doesn't show that you edited it.

Also, just reinstalled the new filter and valve and took it for a short drive. Pinging is still there, but it might have improved slightly.

Maybe it will take time to adjust, maybe it is still consuming oil somehow, or maybe it is something else, not sure. Still a good replacement to do.

99FiveOh · Aug 30, 2011

The reason I asked about the distributor is that it's a common problem I'm seeing around the forums lately where the PIP sensor failing causes a pinging issue. It's happened to me before and I only found it after exhausting all other possibilities. Also keep in mind that if you are still running the original dizzy, it WILL leave you stranded some day. It is almost a certainty. If you buy one, buy a new one and not a reman'd unit. We have seen too many be DOA! Since this is something you'll need to replace anyway, you could try your luck and if it doesn't fix it at least you'll be all set to avoid the dreaded "stuck on roadside with bad pip sensor" routine!

2002BLGT · Aug 30, 2011

Need to find TDC and verify 0 mark on the distributor , I have seen them slip 20-30 degrees out before

99FiveOh · Aug 30, 2011

Very true. Sometimes they slip without any rubber coming out of the back.. if that balancer is original might as well replace it as well since it too WILL go bad if it hasn't already. I'll bet if you put a new balancer on you'll end up seeing the timing is really in the high teens!

Canary94GT · Aug 30, 2011

Yeah as I posted in my list of things checked, I found TDC and the balancer was for sure within 2 degrees. I also do not see/feel any rubber protruding from the back.

Canary94GT · Aug 31, 2011

What I've done today:

- Reinstalled factory air cleaner to see if the CAI was causing issues. The switch didn't change the pinging.
- Tried 89-octane ethanol-fee gas (assuming the station still sells ethanol-free), and noticed little to no difference
- Changed o2 sensors - might be noticing some improvement. Only took for a short drive and maybe it takes some time for the computer to adjust to them?

WhiteCobra95 · Aug 31, 2011

You can completely clear the adaptations by unplugging the battery for a couple minutes. However, if you've already got some miles on it with the new sensors, then it's probably not worth it. Good luck! I hope that takes care of a a frustrating problem. Maybe your sensors were biased on the lean side and it was a lean knock.

Canary94GT · Sep 1, 2011

Reset the computer and took it for a drive. Pinging is still there, but it does seem slightly reduced.

I hope it was the o2 sensors because I don't want to keep driving 20 additional miles for ethanol-free fuel.

Not sure what to do next.

99FiveOh · Sep 1, 2011

Try a new distributor. Like I said you'll need one eventually anyway.

94 GT pinging, help please

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