Yet another pinging thread.

[manimal]

I've gone through most of the threads on pinging here, but I decided I'd ask anyway. I have a '91 OHV 5-speed here with 100K miles on it. Runs very strong, pulls great all the way to redline. The problem is that it will ping heavily while going uphill under heavy load, or at WOT.

Facts:

- EEC passes KOEO and KOER tests with code 11.
- Spark plugs were replaced with Autolites, gapped correctly. None of the old plugs looked oily.
- I'm not losing any oil, as far as I can tell. I usually do 4,000 miles on a change of Mobil 1, and I've never seen the level drop on the dipstick during that time.
- Fuel filter was replaced.
- Fuel pressure tested to be at 45PSI, pressure stays consistent (rises slightly) throughout the throttle range.
- Bought the vehicle used from a well reputed Ford dealer, and they held the vehicle from me for several days while they claimed to be replacing the lower intake gasket. I'm starting to consider checking with them to make sure that they actually did replace the lower and not just the upper. Haven't tried tightening the bolts yet, started to go at it today but realized I wouldn't be able to get my torque wrench in there without taking the hood off. Maybe?
- MAF was cleaned with electrical cleaning spray. I also have a spare MAF that I tried, but no difference.
- TPS was replaced. Not calibrated yet.
- Tried "misting" the engine with a 12oz bottle of water through a vaccuum hose.

The pinging is especially bad at WOT. Under load at mid throttle or above, the pinging is sporadic, but at WOT it is out of control. This led me to believe that the TPS may have dead spots in its operating range. Just today I was fiddling with it, and unplugged the TPS. With the TPS unplugged, the truck does not ping at all, even at WOT. I gathered that this meant that the sensor was bad, and so I replaced it. No change, and so I'm at my wit's end here and asking for any tips.

The only thing I can think of that I haven't replaced that may be of interest is the spark plug wires. They looked pretty good when I did the plug job, but I may replace them soon enough.

Also, how often is the coil the culprit? I may do the coil malfunction test, but I haven't done that before and I don't know how much of a PITA it is.

Thanks ihn advance for any tips!

 

[dogfriend]

1. Did it ping before you installed the Autolites?

2. Maybe they didn't replace the intake gasket or maybe you have a vacuum leak somewhere else. You could try using an unlit propane torch to try to find a vacuum leak. Direct the gas toward the areas where you suspect the leak - if the propane is sucked in the idle speed will rise.

3. You didn't mention the EGR. If the EGR is stuck open, it might cause a ping especially at WOT.

4. Spark plug wires might cause a miss, but wouldn't cause pinging.

5. Ditto on the coil. Testing the coil pack isn't difficult, you need an ohmmeter. There is a good description in Chap 5 of the Haynes manual if you have it.

 

[manimal]

Yes, in fact it pinged when I test drove it. The salesman actually took me over with him to the service department to tell them about it, and they said "oh that's just the intake gasket, we'll replace it."

I haven't checked thorougly for vacuum leaks, but wouldn't I get pinging still when the TPS was unplugged if that were the case?

This truck doesn't have an EGR valve. That would have been my first guess otherwise.

I'll check the coil. Thanks for your response.

 

[dogfriend]

Oops, forgot that the 1st Gen doesn't have EGR.

I think that the reason that you don't have pinging with the TPS disconnected is because the PCM switches into "limp home" mode without the input from the TPS. In the limp home mode it goes into open loop and ignores the sensor data. This is the similar to when you are warming up the engine. It will run slightly rich in open loop, that may account for the lack of ping.

 

[Majisto]

I wonder if running a can of Seafoam or the like will help. It can help break up carbon buildup inside the motor, and that's what pinging normally is, is hotspots inside your combustion chamber causing early detonation. My old Taurus pinged all the time going up hills...

 

[manimal]

Majisto, I probably will run some Seafoam through tomorrow. I can also get GM Top End cleaner. Which is preferred?

dogfriend, that is a good observation, and I was wondering how much the timing, fuel maps, etc. were affected with the TPS unplugged. However, doesn't the computer also enter open loop mode when the throttle is at WOT? If this is the case, I would think that no pinging would occur at WOT.

One thing that I haven't changed yet is the O2 sensor. I completely forgot about that little devil. Though again, I would think that a faulty O2 sensor would not cause pinging at WOT, IF the computer enters open loop in WOT.

My experience with EEC-IV stuff is mainly on the Ford 2.9. Not sure how much differently the 4.0 EEC-IV behaves.

 

[shamaal]

My experience with a 91 Mazda Navajo - same engine. Same symptoms pinging under acceleration
1. Disappeared when using higher octane (93) gas

2. The hotter the engine; the more often the pinging. With the Autozone thermostat at halfway; pinging under heavy acceleration. With the thermostat at > 3/4 (overheating) pinging under any acceleration.

With a Ford thermostat (temp range unk) the gauge never gets over 1/8 and vehicle never pings.
This may or may not be helpful.

 

[Creager]

This is probably why...

My lower intake after 200k miles.

 

[shamaal]

I just changed my heads in April. It took me two days to clean up the lower manifold. It looked like yours.

 

[dogfriend]

Seafoam Deep Creep (in Aerosol can) works really well for taking carbon off. I pulled the head off my Toyota truck back in April and that was what I used to get the carbon off the tops of the pistons and out of the intake manifold runners.