90 aod pinging

james5275

Registered User
Hello all,
Breaking in my rebuilt engine, glad I did a stock rebuild because I'm sure the problems would be amplified if I made a lot of changes. I have some bolt ons that are likely contributing to the ping, I'm afraid I know what the answer is but just wanted everyone's input. Ecm is still on the stock tune. She won't ping in first or second, but the engine is under substantially less load due to tire spin.

In 3rd and od it will ping at any rpm above 10 psi. Seems odd, 10 psi is 10 psi right? Wouldn't think the late model blower and od would contribute here. An interesting note, my narrow band o2's indicate rich while pinging. As soon as I can hear the ping I back off. Haven't made a run at full throttle yet.

List of particulars:
90 aod, .030 bored.
Mls head gaskets, arp head studs
Late model blower, 10% od, raised top
Late model injectors
75mm bbk tb
Ken Wagner DIC
Stock exhaust manifolds, deleted cats, big exhaust from cat delete on back
Stock fuel pump, fresh filter
Mac intake tube, deleted 90 degree tube
Stock new ignition system
4.11 gears

I think the final clue is part of the problem, the original maf sensor electronics are not installed. Long story short, I had to give up my original to fix another car (before I knew better). I have 2 Mafs and have tried running both in the original housing with the same results:
F1SF-12B579-AA- I believe this was from an old cobra motor
F1ZF-12B579-AA- pretty sure this was a 3.8l n/a Taurus.

Since I'm seeing rich on my narrow bands, is it possible the computer is advancing timing too far due to poor calibration?

I've been researching, looks like the best starting point is to get the correct maf first.
Appreciate everyone's help,

JJ
 
First thing I'd do is confirm static timing - make sure the balancer hasn't gotten so old the trigger ring hasn't spun out of position, etc.

As for the maf - disconnecting will let the computer substitute stock/default values...see what happens then.
 
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Good afternoon

You are correct to suspect the mafs. Stock primary part numbers I have seen begin with either E or F. Example: E9SF or F48F. Check the mafs second part (below the primary number). Example: AFH55-03A or AFH70-4A. The 55 number is what I have seen installed on 1989 - 1991. Sometime late during the 1991 year run the mafs number changed to the 70 number. You should be able to find a replacement at the salvage yard.

Hopes this helps.


Good Luck.
 
What spark plugs are you running? If running stock plug heat range they are most likely your culprit, run a colder plugs Autolite 103.
 
I'm running the stock OEM recommended plugs, Motorcraft I believe? Not Bosch for sure, I've had several problems with them. I'll try the 103's as I've seen many good reviews.

I forgot to mention it did this before the rebuild. Use to have straight pipes on the car, didn't notice the ping (loud exhaust) until I put good exhaust on.

I plan to get the MAF back to normal to start then check the balancer. I'll move on from there and report back.

JJ
 
Your stock fuel pump will be close to maxed out with this combo also, have you tried checking fuel pressure under load? I bought a cheap fuel pressure gauge kit at autozone attached it and ran it under the back of my hood. The gauge just makes it to the windshield.
 
Thanks for the input. Checking the fuel pressure at load is on the list. Dave, pardon my ignorance, 8.xx:1 due to the injectors and maf? My thinking must be off, 8:1 is rich correct? If mixture is rich, is high act causing detonation? I'm enthralled with tuning and driveability but just haven't made myself learn yet. I'll search more, Ig 'm sure you've explaineed this plenty before.

JJ
 
Your injectors are 20% too big - 36's instead of the 30's that your EEC thinks you have. Therefore that means 20% more fuel which means instead of the 11.0 AFR that is commanded under boost, it's more like 8.8 AFR. Gasoline engines do not run with that much fuel. Most likely the only saving grace in your situation is that the stock fuel pump can't put out that much fuel so most likely fuel pressure is dropping, otherwise it wouldn't even run in boost. E85 would run at 8.8 AFR, but that was really more tongue in cheek than an actual suggestion because 36lb injectors would only support stock HP levels before maxing out anyway with E85.

The only reason the car runs decent at all is that the adaptive nature of the EEC is capable of compensating up to 20% (how's that for a coincidence) in part throttle. Of course that results in a bunch of part throttle drivability issues, but maybe that's not your biggest concern right now. Once you go into boost the adaptive nature of the EEC is muted and you basically "get what you get". In your case attempting to use narrow band 02's as an indicator of what is going on is worthless because all they tell you is that the mixture is richer than 14.7. Since mixtures from 14.7 to about 13.0 are too lean for boost and won't make enough cylinder pressure to detonate, you won't hear that ping, but 12.9-12.4 will ping pretty bad and you won't know anything about it. Keep in mind that the EEC is trying to run 8.8 and can't, so you are somewhere in between. Most likely it starts out super rich, then passes through the safe range of 11-12 as fuel pressure drops, and then ends up somewhere in the danger zone when you run out of fuel pump and MAF sensor range. You are oblivious to all of this because all you know is that it's richer than 14.7.

If you "fix" any of the possible issues you'll probably make things worse.

A bigger fuel pump will make it actually run even richer. AFR's richer than 10.8 will just tend to foul the plugs and ratio's richer than 10.4 will generally cause misfires and what is often called "fuel knock". 9.0 and richer really won't run at all (on gasoline). You may be experiencing some of that at lower rpms already - then possibly a lean knock at higher rpms as well.

Changing the MAF is a crap shoot. Factory MAF sensors are not calibrated for any injector size, that's just a bunch of aftermarket whooey. No factory MAF is calibrated. Period. They have output curves and ranges that are hard written into the EEC. If you take a MAF from a car that was intended to make 100hp, then the sensor will be fully saturated at about 140hp and will not output any information above that power level. Period. if you take a MAF that is intended for 400hp, it may read all the way to 450hp (the OE always puts in a margin of safety) but the shape of the curve will never match your pre-programmed EEC curve, so no matter what rpm or load point you are at, the signal will be wrong and it will run like crap.

Anytime you think "calibrated maf" that's aftermarket speak, so that means aftermarket only. Calibrated MAF's were intended to work without using a chip to tell the EEC what size injectors you have, but the science is sketchy and I don't recommend relying on it. Even with a calibrated MAF, you still need to tell the EEC what the hell you are doing.
 
Good morning

If I understand the information correctly Mr. XR7 Dave the bolt on "mod" with 36 pound ejectors requires a tuned EEC (1989 - 1993). Now before I get "dinged" for not knowing any better I have been slowing collecting parts similar to James 5275 and had assumed it would be pretty much straight forward bolt on upgrade. I am aware of the fuel pump upgrade and would have including it in my list. Having not tuned a car before and a little wary of so called local turner(s) would I first bolt everything on then purchase a custom chip from you before driving the car?
 
You could sneak by for a bit if you use the stock MAFS for the SC, and install a C&L MAF housing with the correct sampling tube per the chart. I have done this years ago and it still did require a custom tune to get it all dialed in. What Dave is telling you above is 100% correct.
 
Dave and everyone, thank you again. Dave, I cant tell you how many of your posts I have read. Everything makes 100% sense, especially rich mid range transitioning to lean high load, which is what I suspected. I knew the narrow bands were not desired, now I know why.

So, the to do list prioritized:

255LPH Fuel pump
Proper MAF, Tune, (need to research)
103 plugs suggested (need to research)
widebands

We'll work through this together Sam!!

Dave, do you have any planned trips to Omaha with Ken Wagner? He's always stewing up something.

JJ
 
Summer work

Following up from the spring, did a lot of work on the car with good results.

Installed a fuel pressure gauge, clearly witnessed the fuel pressure dropping off under load.
Installed Auto lite 103 plugs and 255 walbro pump. Instantly found the fuel pressure maintain even under wot in od, but still had a slight Ping, and verified on the narrow band o2's. Switched to 100 LL fuel, great improvement but still had a very minor ping at the highest loads.

An interesting note, I feared engine damage due to an audible tapping only at idle. It strangely surfaced immediately after installing the fuel pressure gauge. Since installing the 255 pump, no more tapping at idle. Very strange. May have been injector noise traveling the steel braided hose? Gauge is mounted on the cowl.

Ran out of money with other repairs on the car. Wheel spin was killing me, had to throw on a new pair of fattie Coopers on the rear then started brainstorming.......

I know you experts will be upset, but I played with inserts inside the maf. Cross sections of coupling hose to reduce the inner diameter, which subsequently adjust the airflow through the sample tube. Thicker inner liner=reduced cross section=greater velocity of air through the sample tube. First attempt went WAY too thick and she ran pig rich, wouldn't idle at all.

Bear in mind, at a young and dumber state of mind, I gave up my original sensor. The 90 style housing didn't offer the adjustability I was preparing for.......so ended up going with a ford 90mm.

Through trial and error, she idles nice and buries the needle on my narrow bands under high load. No ping heard, but I understand the tune is still not correct. Driveability not suffering at all, which is very surprising. No more WOT runs until spending more $$$. Not a permanent fix by far but makes me much more comfortable to poke around on the weekends.

Still NEED proper maf, wide bands, and tune, on the list. Critique away!!!!!!


JJ
 
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