mild pinging at cruising speed

[conradcr]

I have a '91 Explorer.
During the summer (when the outside air temp is greater than 100deg.) I get a mild pinging when cruising down the highway. If I let up on the gas or step on the gas, the pinging goes away. The engine temperature is right where it normally operates even in the winter. It seems tied to the air intake temperature. I have tried higher octane gas and there is no difference. I have experienced this problem for two summers now and during the winter, everything runs smoothly. Any suggestions?

 

[leenjen]

if you really think it's the air intake, why not try a KKM or K&N (there's lots more, but these are most popular).
maybe that will help, it couldn't hurt.

 

[irtySanchez]

i had the exact same problem for a few months. It only happened on the freeway and only at certain speeds and RPM's. I was stumped as to what it was. I took it to a local shop. Myself and a mechanic took it for a ride and he said that it was definetly pinging. It was determined that the MAF needed to be cleaned. It was done and it has not happened since. Give it a shot. GOOD LUCK!!!

Brad

 

[conradcr]

I am not sure where exactly the MAF sensor is located on the engine. I have found descriptions of what the body looks like and have seen pictures of the wires themselves but I am not sure which sensor on the engine is the MAF.

 

[Rhett]

A KKM could make the pinging worse, since it sucks in hot underhood air in the summer. However, if you can get cool air to your KKM via a tube mod then you'll be better off performance-wise because of the air a KKM can move...

I can add that my truck was still pinging just a little during hot weather, in just the conditions you say... on throttle "toe-in"..that is, when first hitting the gas and letting off, not at wide open throttle. That was last week. Over the weekend I bought some Cool Tape and insulated the whole intake duct, airbox, etc. and now, on the same tank of gas, it doesn't ping at all. I have found, though, that I have to run mid-grade. Still pings at 87 octane. I may have to see if it does now that I have insulated the air intake.

 

[Maniak]

It is very easy to find the MAS on a first generation (like your 1991).. Find the Air clearner.. (passenger side fender).. There is a metal piece between the air filter box and the air tube (the tube that comes from the front of the motor, across the front to the air filter)..

The MAS is in that metal thing that the air tube plugs into. There are 2 Security torx screws on the top. Decent tool stores and good auto parts stores will carry the security torx bits.

~Mark

 

[oahrens]

Wait till tomorrow----

Hey conradcr--

I had a similar Problem with my 91 XLT with 4.0 and 80,000.
Here's the thread--

http://www.explorerforum.com/forums/showthread.php?threadid=29449
--------(shameless plug?)-----------

}{ Back to the subject.... I just bought a new DigiCam and will take pics of exact locale of MAS and cleaning process....will also be posting step-by-step pics of FPR swap-out.

So stay tuned...will have the story at 11 !......

 

[Nate]

FPR swap-out?

 

[jjue]

My sister's '94 Explorer was having pingin problems at cruising and passing speeds as well, espcially when pulling up a hill. Anyway, I went back to the basics by changing out the spark plugs and the plug wires. As a result, the pinging was gone. I don't remember y'all mentioning that the check engine light was on, so please check this first. Apparently, when I was driving it, I forgot to change the plug wires at 60k, and the wires were the original with over 92k miles. As it turned out, I needed a base ground to start with, and the plugs and wires are pretty much the most basic.

 

[Rhett]

You guys have hills in Mississippi?

hehe

 

[conradcr]

I found the MAF and cleaned it with carb cleaner. Just looking at the wires the thing looked to me to be in brand new condition. I drove yesterday afternoon and still had some pining (outside temp 110F in Phoenix). By the way, the MAF was held in by two philips headed screws instead of the saftey screws everyone has been talking about. Also, It appears that there was some sort of torque seal (anti-tampering goop) applied to one of the screws and hadn't appeared to have been broken in the past, so I assume I was the first one to pull MAF since it was installed.
What is the FAP that was mentioned earlier and where might it be located?
Thanks,
Conrad

 

[Rhett]

That's the FPR...Fuel Pressure Regulator...if you have the 4.0 OHV it's located on the fuel rail, which is on top of the engine, a little on the passenger side. It will have a fuel line running into it as well as a vacuum line.

I'd suggest you do a search here as there are lots of FPR threads that tell all about how to diagnose a potential FPR problem, how to check for fuel in the vac lines, test fuel pressure, and so on.

 

[jjue]

Originally posted by Rhett Browning
You guys have hills in Mississippi?

hehe

Yep, that's what happens when the dirt is nothing but yazoo clay. We end up with hills potholes. Either way, even the slight changes in elevations caused the Explorer to ping under load.

 

[rockylaurence]

They all PING!

Mine had the same problem but was really bad at Interstate speeds. Under warranty they replaced the MAS. Later, a lesser Ping developed that I couldn't get rid of. I tried everything, Cleaned MAS, ran cleaners, etc, etc. I spent 2 yrs on 93 octane. However, and I'm afraid to mention it(it might come back) I dumped two bottles of Valvoline fuel system cleaner in a 1/4 tank of gas and the problem has cleared--Crazy! I must have run 10+different types of cleaners through following their instructions and had no results-period. I've run 3 tanks of the 82 with no PINGS.