I have a 94 explorer with 106k miles. Engine sounds great when cold. However, after driving for 10-15 minutes or so it will ping when either going up a hill or after jumping on the gas. Here's what I've done to try to correct the problem:

Cleaned MAF sensor - helped a little
TSB to decarbon the combustion chambers/intake - helped a lot
New EGR valve - no help
New EGR pressure sensor (DPFE) helped a little
New Plugs and wires - no help, but needed replacing anyway

If anyone has any ideas/suggestions/past experiences, please share. Also, just curious, but it's probably time to flush and fill the coolant. Would changing the thermostat to one with a lower temp help at all?

Thanks

 

I responded in your thread about the thermostat. Try the lower intake bolts as I suggested there, and also check carefully for vacuum leaks and air intake leaks. There were some other things I suggested there as well.

 

I have a 94 XLT that had the same problem. I tried the same things you did and it did not help. However....

Try this:

1) Check lower intake bolts.. especially the number 5 cylinder (left middle)

2) Pull the MAF sensor again, spray with carb cleaner. Inspect and brush GENTLY with a toothbrush..Make sure that it is completely clean. BE CAREFUL NOT TO DAMAGE THE ELEMENT

3) Disconnect battery for at least 1/2 hr.

4) Reconnect battery and take out for a test drive.

5) Drive it HARD for 15 min or so to get the computer relearn proper settings.

I did this and pinging is gone.

My next steps were to bring it in to teh shop and have them check for bad sensors (EGR, O2).. anything that affects timing.

Let me know how you make out.

Chris

 

Forgive me for asking a stupid question. Where exactly are the lower intake manifold bolts? I can't see much of anything under the upper manifold. If you could describe where they are, say in reference to the valve covers (or some other landmark), I'd appreciate it. Also, I used my voltmeter to pull the codes, and assuming that I'm reading the pulses correctly, a code of 33 appeared - egr not opening, insufficient flow. I poked around the vacum lines a little, and one of the connectors is a little lose. I stopped and bought vacum hose, hose clamps and a few boots. I'm going to try to make sure that there isn't a vacum leak somewhere. I'm reasonably sure that the egr valve and dpfe sensors are ok, since I just replaced both.

 

There are three "fingers" on the upper intake that feed air into the lower intake. The gaps in between are your access points to six of the lower intake bolts. The first time I did it, I had to clean some crud out of the pockets there to find the bolts. Two are against the firewall. And the other two are up front near the thermostat housing (The thermostat housing bolts to the lower intake manifold). Some people choose to remove the upper intake manifold to make it easier to get at the bolts. It can be done with the upper manifold in place, but it will require some fancy socket extension work for a couple of the bolts.
I'm not sure you read the pulses correctly. Your '94 should be putting out three digit codes. The two digit codes stopped in '91 or so. My guess is, what you interpreted as 33 was really 111 repeated twice.

 

Thanks for the info. I'll have to hunt around under there and find the bolts. I don't doubt that you are correct about my not reading the codes correctly. There were 3 pulses a second or two apart, then a 4 second pause, then the 3 pulses repeated. I guess that the long pause was separating the codes, and not separating the digits. At least this was a pleasant surprise that there are no codes being thrown....Thanks again.

 

Ok, I tightened the bolts. Each one was 1/4 - 1/2 turn lose. I just reconnected the battery after about an hour of being disconnected. I'll go hard on the way to work tomorrow and let you know what happens. Thanks.

 

Hi Everyone.

I just finished working on my Mothers 94 Explorer. It had a real bad problem with engine knocking/ detonation, on any type and kind of fuel, even super premium. The check engine light came on and stayed on frequently. I had Autozone do a free code scan, and the code came up with "rich limit reached, out of range" (OBD1 code # 86 I think).

I did a bunch of research and planned on replacing the knock sensor and EGR valve. I did a bit more final research, and came across the suggestion that the problem was a sooty/dirty MAF sensor. This is the site that I got the info & instructions from can be found at this web address:

http://www.glue.umd.edu/~singletn/web/pages/ping.html

I never thought that this would be the magic bullet that it turned out to be, but boy was I surprised.
The MAF sensor is right after the Airbox. It requires a special Torx type tool to get the 2 screws off. They have metal stud guards in the center to prevent the Torx being used, but you can hammer these down with a pin punch (carefully!).
Be careful of the MAF, clean the 2 diode type elements with Carb cleaner & reinstall. Reset the truck system computer by removing the Neg & Pos battery cables for about 10 mins.

You now have a truck & engine that goes from being ready to blow from detonation to running like brand new. A true magic bullet. I still may change the EGR valve, but the Knock sensor is going back.

 

I'm glad that cleaning the maf sensor worked for you. It didn't for me. After tightening the lower manifold bolts and resetting the computer, it seemed to run a little better today, but I'm going to wait a few days of normal driving (I drove it HARD on my way into work today) before coming to a conclusion about if the knocking is gone or not. Mrshorty had menitoned that a 94 should be spitting out 3 digit codes and not 2 digit codes. Not that I'm doubting Mrshorty, but can anyone confirm the number of digits in the error codes?

 

Ok, so I cleaned the MAF sensor one more time....the pings appear to be gone - completely. The only differences are this time I used carb cleaner instead of brake cleaner, and I scrubbed the filaments with a toothbrush - extremely carefully. I didn't just go at it. What I did was to put the filament about 1/2 way down the bristles in the brush and use them to scrape across the sides of the filaments. They looked brand new before this cleaning, and exactly the same after. I guess that the brake cleaner that I used left some kind of a residue. Any way, the truck drives like new again. Thanks to everyone for all of the suggestions. Here's everything that I did to try and correct the problem:

Cleaned the MAF sensor
New EGR valve (original was still on there)
New EGR pressure sensor (original was still on there)
Decarboned the combustion chambers with PM3
Tightened the lower intake manifold bolts (all were about 1/2 turn lose)
Cleaned the IAC valve and throttle body
Replaced some questionable vacum fittings
Cleaned the MAF sensor again and drove to work the next day with the radio off and a big smile on my face because I only heard the sounds from the engine that I was supposed to hear!!!

 

Glad I could be of help!

 

I posted in the Ranger forum the entire TSB issued by Ford concerning pinging/knock on the 4.0L engine back in Feb of this year. The TSB concerns carbon buildup and removal, you may want to read it and implement it. This is a common problem and implementing the TSB should help.

 

I had already done that. I'm the guy that you em'd the picture of the throttle body/cannister purge line. Remember me? Anyway, decarboning the engine did help, but the ping was still there. After scrubbing the MAF sensor with carb cleaner and a toothbrush, there are no pings at all on 87 octane. Thanks for the suggestion though...

Matt

 

See the below. This is from "http://www.glue.umd.edu/~singletn/web/pages/ping.html"
I did this after trying all the other "fixes" and my pinging is gone, w/out affecting my mileage or power. "Your results may differ".
I did NOT reset my X's computer by disconnecting the power, but did remove the plug w/the key off.

"Our car has an "octane shorting block" that can be removed to retard the ignition timing by about 3 degrees. Upside is that the pinging will almost assuredly be eliminated. Downside is that performance and economy will suffer if you do this. Since these are marginally acceptable at best, save this as your "last resort" solution.
The octane shorting block is located under the hood, in a harness just to the rear of the fuse box. So if you are standing at the right front corner of the car with the hood open, move to the rear a bit to the fuse box. Now, look at the rear of that fuse box for a big bundle of wires that goes toward the firewall and somewhat down towards the engine. It's about 1 inch or so in diameter, wrapped in plastic tape. About 4 or 5 inches back on this bundle, from the fuse box, locate a pair of wires that come out and are folded back against the bundle. These are maybe 4 inches long, and go to a plastic socket that's maybe 1.25 inches wide, taped back on the bundle (at least on my car.) <mine was not attached to anything, and was a gray color>In that socket is a rectangular plug, maybe 3/8 inch thick. This is the octane shorting block. Remove it and store it in the glove box. Pinging, gas mileage and performance are all gone now."

good luck.,
Td

 

I wouldn't recomend doing this. Again, read & re-read the "use as a last resort" part. Also the gas mileage & performance are gone closing part.
In addition, you are not taking care of the true problem, just using a drastic cover-up.
Just my 2 *****!
-Chris