this truck is driving me insane, it seems to like to ping, first it was a dirty hot wire in the mass air sensor, cleaned it ran good for a few weeks, then pinging again, found it to be a vacuum leak, put a new hose on, ran good again for a few weeks. now pinging again, the only difference now is it will only do it when its at full operating temp. what could it be now, i cleaned the hot wire again and inspected all the vacuum lines and no improvement. the fuel filter, air filter, plugs, wires are all less than 3000 miles old, it has had the fuel injectors cleaned professionally in that time also. i 've had the egr apart and everything is open there, no plugged passages or anything. the truck is a 1997 f150 with the 4.6 and it has about 50 thousand miles on it. any help would be greatly appretiated.

 

Sounds like it may need the PCM reflashed at the dealer. There were detonation issues on some of the older trucks from too much advance in the timing.
By the way, have you checked the fuel pressure to make sure it is up to par?

 

Good to know that I am not alone with this nagging problem. I've got a '97 150 with the 4.6L too. Everything else is fine with all other components and systems but I cannot seem to shake the pinging.


Are there any famously common weaknesses that may produce pinging that other owners are aware of?

 

Lean, hot, and carbon buildup. There's a TSB to run over 3000 RPM every day. It went from really irritating pinging to none at all just by running it hard 15 or 20 seconds every week or so. The cheapest fix (maybe 50 cents of gas a week) ever.

But bad O2 sensor, MAF, vacuum leak, plugged filter, weak pump, bad regulator, etc can cause lean, that'll do it. Running hot (thermostat, plugged radiator, weak fan clutch) will do it. Carbon buildup will do it.

 

That is the best reply to this issue yet. I'm printing your message and taking it with me to the mechanic.

 

it shouldn't be carbon build up, i had the heads off in december and everything looked surprizingly clean. but i will check the other stuff. thanks

 

I have the exact same truck and same problem Rcmgiasson . If you find out what it is please post.

 

I had the same problem and never figured it out.I installed an AF1 and haven't heard it again.I thought it would be worse since the kit draws warmer air from under the hood instead of the fender.I'm not saying the AF1 fixed it but....I had cleaned the EGR checked for vacuum leaks and had a motor vac with no luck.My truck runs well but on occasion will stall immediately after ignition(no chance to idle).This makes it a timing issue for sure IMHO and had given up.No one ever mentioned a pcm reflash but it probably wasn't offered when i when looking for a cure in the early days.I alway drove this truck like the pistons were made of glass.now i can't stop beating the hell out of it.No b.s
cheers

 

ok a little clarification on how this system works is needed. Since the trucks runs perfectly until it reaches operating temp, could it then be a problem with one of the sensors. It was my understanding that the system didn't start taking info from the sensors until full operating temp is reached. wouldn't that cancel out the need to check for a vacuum leak and fuel pressure. wouldn't that narrow it down to one of the sensors. could someone clarify how this system works. thanks.

 

The system uses all sensor input before it is at normal temp. It is lower like around 140 to 160. I have watched this with my Diablosport Predator.

 

You're probably referring to fueling. The system starts on simulaneous mode, where all injectors fire as soon as the motor starts turning. As soon as it derives the phasing from the CKP and CMP, it begins normal, open loop fueling.

Open loop fueling is measuring the incoming air (MAF) and using a lookup table determines the amount of fuel to inject. It is very similar to a carburetor, using the amount of air to determine the amount of fuel.

When the truck warms up it switches to closed loop. Here it uses the pre-cat O2 sensors to 'adjust' the mixture instead of blindly following the tables programmed at the factory. There are other secondary uses like feeding the cat with quickly alternating slightly lean/rich mixtures to keep it warmed up and efficient.

The truck starts briefly (one or two crank revolutions) on simultaneous inject. Then runs open loop until the O2 sensors warm up, then switches to closed loop. The only other time it falls back to open loop is wide open throttle enrichment and limp home failure modes.

Mark

 

Sorry, I lost the point. Before closed loop (when the O2 sensors are warmed up), it is still using many, many other sensors (CKP, CMP, CHT/CTS, TPS, MAF, etc., etc.). The only sensors it ignores are the O2 sensors. After they warm up and you enter closed loop, all sensors are used. If your problem exhibits on cold starts, it isn't the O2 sensors. That's about all you can say.

 

i would call the dealer about the reflash before you spend to much$$.The reflash must be new because my truck was at more than one dealer over the detonation issue and was never fully resolved.I bought the truck used from the original dealer and have many printouts from the vehicle records regarding this.Also i was told some trucks did it right off the line.I don't know the exact sequence of operation but the other post sounds about right except mass air systems actually calculate air density.Speed density systems use tables.This is why mass air systems accept some mods better than speed density.My truck acts exactly like the initial timing is slightly over advanced.With the AF1 it still stalls about 1 out of 10 starts but no detonation can be heard under any driving conditions Why i don't know but im not complaining .The IAC and Egr were replaced more than once plus had checked for vacuum leaks with propane many times but found none and it still did it in both hot and cold weather.I was at a loss to figure this out since there was no way to retard the timing as in the older cars.I wonder how aggressive the new tune is?I bet all it does is retard the timing which may make it bit of a dog.This may not be you problem but the regular dealer fixes made no difference.
cheers

 

I changed my MAF sensor and it fixed my problem.

 

matt,

There is a table for fueling after the air mass has been determined that is kind of like a spreadsheet, rows for RPM and columns for load. Each cell contains the modification to injector pusle width for that RPM/load. In closed loop, these cells are the ones updated by O2 feedback and used to correct fueling. In open loop, the last long term numbers are used as a static correction. In OBD-I, they were called block mode and integrator numbers, today we call them short term fuel trim and long term fuel trim.

You are right that there are also tables for converting MAP/RPM for speed density or TPS/RPM for alpha-N (the fallback for our trucks if the MAF fails) to grams/second (along with calculated corrections for density altitude - BARO and IAT). And you're also correct about the effect of mods, especially intake, exhaust, and cam mods, that would affect the volumetric efficiency which don't affect the MAF.

Mark