This is a recent development. BigRed has started pinging (detonation) under load at highway speeds. No pinging on takeoff or initial acceleration, but cruising down the highway at 60-70 mph. If I put some pedal into it, especially on any upgrade, she starts chattering away. Sounds like it is coming from #4 (passenger side rear), but at 70mph it is understandably difficult to be sure.
I have been elimating possible causes one by one with no luck. I switched my computer program back to stock (Superchips programmer), removed my
Pro-M MAF and re-installed stock, disconnected my MSD-6A and hooked up stock. I performed a tune-up not too long ago, including brand new Taylor wires. I always run 93 octane, so that is not the issue. I have run three or four tanks of fuel through her as I have been looking at this problem and went to a couple different stations to ensure fuel was not part of the problem.
She runs and idles fine, no perceptible change in power (except for expected loss when I take one of the bolt-ons out of play). Checked the timing, rock steady at 10 btdc. I have disconnected the battery after each bolt-on removal to force the computer to re-learn the curve.
1996 Bronco XLT
302
12500 Miles
Not throwing any codes

I am running out of ideas, anyone got any new ones?

 

Did you check your spark plugs?

 

your "knock sensor" may have gone bad. if you dont know what it is, it detects detonation in the combustion chamber, and sends a signal to the ECM to retard the spark slightly to stop detonation. look in the haynes manual, it should tell you how to test it, or if you dont want to bother testing it, you can replace it. advance auto has em for about $35

 

Have you run BOTH tests (KOEO and KOER)? A dead KS (knock sensor) should trigger a code but will ONLY return the code during the KOER test. The KOEO test will not yield this code as it is not a stored memory code. Its a PITA to get to if it has failed but the 302 does utilize the KS to control detonation. You can "test" the KS by smacking the block or the intake with a mallet while its running. If the KS is good, you should hear the engine rpm's change as the ECA compensates spark timing because the KS "heard" the ping.

 

Even with a bad knock sensor, it shouldn't knock with with factory timing on 93 octane.

 

Aurgathor, yup, replaced the plugs during the same tune up when the new wires were installed.

Grey, she is a 96 with OBD II. Stored codes are stored codes with this system, KOEO/KOER does not apply. I have both my Superchips programmer and an Actron OBD II Scanner to read the codes with.

Just in case I will give it the mallet test... thanks guys and keep the ideas coming.

 

How did the old spark plugs looked? Did you see anything unusual?

Are you sure it's pinging and not valve train noise or something else?

 

what kinda plugs are you running?

 

1) Check codes first.
2) I was able to determine my issue was a bad Throttle Position Sensor (TPS).
3) There is a voltage test you can do to see if it is within range. Should be able to find it in your haynes manual or on Fordfuelinjection.com.

Good luck...Merry Christmas!

 

Oh well, $%^t... I missed the "96" part. The mallet test should still be a decent indicator.

 

Big Red, I'm running the same mods as you on a 94 with a 5.0 mine has started spark knocking also sense the weather is colder. I replaced the knock sensor last yr. that's a job with the upper intake on. I've backed my timing from 12 to 8 btdc. and I still have spark knock when cruising in OD. I cleaned my mass air sensor and switched gas companies and it has helped, but my Bronco allways runs on the lean side.

 

Aurgathor, old plugs looked normal, no unusual fouling or discoloration. Yes I am sure it is detonation (pinging, pre-ignition) and not valve train noise.

CJe07, as I said, no codes. Didn't think about the TPS because of the no codes thing, but the voltage test is a piece of cake and only takes a few minutes (done it many times). Might as well check the TPS, at least if it tests fine I can rule that one out...thanks.

KB, running Accel U channel truck plugs.

94 XLT, been running the mods a long time with no issues at 10 btdc. Pinging issue is a new development, so logic dictates there must be a cause. The "fun" part is figuring that one out.

Thanks for the input guys, and keep throwing the ideas out there. Put a couple of cans of SeaFoam in a fresh tank of gas today, and ran a can through the intake tonight. We'll see if that makes any difference.

 

Actually, I was thinking about white or very light colored plugs (which may not appear to be bad) and a mixture that is too lean. My vote goes for the O2 sensor ATM. Not sure how to check it for proper operation other than replacing it.

Does anyone know what the output on it should be when the engine is fully warmed up, and measured with a good, high impedance multimeter? (in-circuit, of course)

 

The normal operational voltage for an O2 sensor ranges from 100mv (millivolts) to about 900mv with a tolerance spec. of about another 30-50mv in either direction depending upon the unit. The midpoint or crossover voltage is right at 450mv. Any voltage reading below 450mv is read by the ECA as being "lean" and any reading over 450mv is interpreted as being "rich". So during normal operation the voltage reading from the O2 sensor should be really close to 450mv or 0.5vdc.

 

So one way to trick the ECU into enriching the mixture is to connect a resistor (probably something in a megaohm range) between ground and the output of the O2 sensor. One can just make a small harness that goes between the O2 sensor and its plug, so no changes are needed to the factory harness, and if it doesn't work, it's easy to go back.

If the O2 sensor is slightly defective (gives a richer reading) the ECU will try to compensate for it by makng the mixture leaner until it gets a value to its liking.