My cheapo Walmart decoder does the same thing!

 

Can anybody tell me which vacuume line to use and where to find it so I can pull it to suck up a can of this "Sea Foam" engine cleaner?

 

Does a tank of premium decrease the knock? Just for diagnostic purposes. what is the altitude that you operate at?

Ken

 

best place is a small neoprene 1/8 or 3/16 hose into front of throttle body after sliding back the black air hose, gives the best most even distribution among all 6 cylinders
can use large black vacuum line to vacuum brake booster on fire wall driver's side, not as even distribution to all cylinders.
use whole 16 oz can into hot engine at 2000 rpm, let soak for at least 1 hour, then out to freeway and run the girl hard, like you just stole a Corvette.

did you try water into the plenum, best combustion chamber carbon remover there is and the price is right, 1 pint to 1 quart does the trick at 2000 rpm, some say to use deionized water if you can find it, but engine sucking in normal polluted air moisture while running and no harm done

there is a Octane Plug in the electrical wiring to the PCM that reduces the base and total run timing by 4 degrees, will throw a code all the time plug is out but may get you by until the pinging cause is found.

 

Normal opperation at 6200 ft. ping gets worse as I go lower (doesn't make sence does it?) Premium gas makes no difference. Hot day ping is worse. Damp cool day (denser air) ping is a little better.

 

Thanks for the suggestion on how to administer the Sea Foam, I'll give it a try. A year or so ago I tried everything under the sun to get rid of the ping, new plugs, wires, fuel pump, MAF sensor, fuel filter, etc, etc, etc. Finally got disgusted and parked the beast. Now I have a little time again so I'll go back to work on it. I have read that this engine runs real close to being too lean so as to comply with some polution spec and that it is easily pushed over the top into a ping situation. By the way, this is/was a California car and I know their EPA specs are a lot tougher than the rest of the country. (There are 49 states and then there is California) . I have also read that Ford is adamant about not increasing the gasoline grade, and at todays prices I can't affort to do so anyway. One last question: Any chance I got a bad MAF sensor when I replaced the one that was in use? Are rebuilts any good? and is there any way to check them?
Tom

 

any codes, CEL only lights on major codes.
may be the O2 sensors, how long since changed, the front one sets fuel/air mixture, rear one measures NOxide levels. Bosch is the manuf of Ford's original equip O2's, they recommend replaces heated type O2's every 100k miles or when failed, they get contaminated and become slow to respond or out of tolerance. can cause rich or lean condition depending upon failure. disconnect battery neg. lead for 10 minutes if O2's changed to reset parameters memory in PCM/ECU

many auto parts stores are set up to test MAF's for free, try Autozone or call others. also will read codes for you or loan reader for instore lot use. some states have crazy laws that don't allow auto parts stores to read or analyze codes.
post codes on forum, lots of help here

rebuilt MAF's are ok, only part replaced is sensor/heater element, then calibrated per electrical characteristics and air flow.

Ford designed the 4L pushrod with no ping/knock sensor, not one of their better ideas, all lean burn engines need a knock sensor to avoid self destructing, most drivers will not pull over for pinging, can kill an engine in minutes. V6's run rough to begin with, no need for engine knock to really shake, rattle and roll the motor mounts.

 

Daddymouse:

Did you look at the transmission modulator? If the diaphragm broke and let tranny fluid into the intake, you'll have pinging.

 

Daddy Mouse>
your '91 4L does have a vacuum modulator on auto tranny
copper is right, vacuum modlator can leak ATF into vacuum line> intake and cause pre detonation knocking without affecting shifting, check neoprene vacuum line into vac. modulator on passenger side tranny near middle, any leaking ATF in line=replace modulator and change engine oil=contaminated by ATF, then do the Seafoam or water DeCarbon treatment.

what brand and part # of plugs did you put in, 4L's are especially critical of plugs, only Motorcraft or Autolite double platinums and correct heat range part #, search Aero forum for #'s, either brand will last another 100k miles or more. wrong plug, too hot heat range, can cause pre detonation knocking. talking with my family which have owned 15+ 4L's in Rangers/Explorers/Aeros last 15 years, they all have went to Autolite double plats, confirmed addicted Champion in Ford users for decades but Champs don't work in 4L's, now they all own SD TPS, no spark plugs just stink and noise

 

Looks like I have gotten five or six really good sugestions about how to attack the ping problem. Guess I'll have to go try to fix the beast now. Thanks to every one for all your help. I'll post the results as I go. Thanks again.
Tom