My recently aquired 1989 F150 XLT (302, AOD) with 96,000 miles, has severe pinging under any kind of load when running 87 octane. I switched to 89 and the problem is almost gone...only very light detonation can be heard and only in overdrive when accelerating. Is this normal? do I have to use 89 forever?

I don't know if it has any relevance, but, sometimes (and I haven't been able to isolate when), I have noticeable idle fluctuation when the engine is cold; it idles high, then there is a click, and the idle falls, then climbs back up, then another click...

...there is also a loud mettalic "click" (but more than that) from the front end, drivers side, when the brakes are first applied, but only sometimes. No connection to the preceding questions but it doesn't sound good.

Sorry for the multiple questions, I am a new F150 owner (my old 67, F100 was much simpler), and not a great mechanic, though I don't mind trying to fix things as long as there are fairly clear instructions. Any pointers would be much appreciated.

 

What you are describing sounds similar to when the A/C pump is cycling.

 

Check your #7 and #8 spark plugs wires and make sure they are a) not touching and b) not running parallel to each other at any point.

 

I havn't used the AC yet since it is a bit too cold for that in Missouri at the moment!!

I will check the plugs, that could be the problem.

Thanks for the advice

 

The A/C will run if the defrost is on.

 

Thanks, I hadn't realised that the AC did that...I checked this morning and that seems to be it, I've never experienced anything like that kind of fluctuation though on any other car I've had.

I have heard about crossfiring on this forum but don't really know much about it. Would crossfiring between #7 & 8 change because of using a different octane? And is there a diagram or something to show how the wires shoud be routed?

Thanks

 

Having RECENTLY experienced SEVERE crossfiring on #7 and #8 with NO external indication of leakage, the only advice I can give you is keep them as far apart as possible and if you do have to get them close, make sure they cross at right angles. Now, this is assuming you have the 15426378 firing order I have. I saw something in here yesterday, though with a REALLY WEIRD firing order on a 5.0. It did say for the Bronco, and was written mostly in French, so I assume the photo was of an underhood sticker on a Canadian Ford. I'll search, and come back to point at the message I saw that in. Was from one of the more knowledgeable folks in here too.

 

The newer truck 5.0's, both US and Canadian markets, used the 351 firing order, pictured in that other thread you are speaking of (it's really nothing weird at all). You are right that the 7-8 crossfire problem is only for the standard 302 firing order. Since it is inductive crossfire, you shouldn't see any external signs of current jumping from one wire to the other. Simply the current through one wire induces current in the other parallel wire due only to a magnetic field created by the first wire. Based on the right hand rule, current can only be induced in parallel wires and cannot be induced in two wires that cross at right angles.

 

TYVM for the clarification. Seems I do remember reading some discussion about switching to the same timing as the 351 with MAF systems in later models. That sticker just looked very weird to me, especially since I haven't seen that under the hood of any Ford in Alabama in a LONG time. I've searched high and low for a similar diagram for routing the wires on my '92, but just tried some hit/miss combinations til the cross-firing went away, at least most of it. Still got a bit of a stumble in the idle and can feel it out on the highway too, but the heavy throttle bucking and snorting is gone. I checked my TPS with a meter, and it looked smooth while I was turning the throttle, but yet when I'm accelerating, moreso while I'm increasing throttle slowly, I can feel what seems like steps in the power. I dunno if this is the ECM selecting different points in the fuel tables, or a TPS that isn't as smooth as I thought. It's a pretty weird sensation. Being an electrical engineer has it's advantages sometimes, but Fords manage to invalidate a lotta things I've learned about digital control systems in the past 25 years. Still love my Fords, tho.