I recently purchased a 1989 F150 4x4 302 (EFI).

On it's maiden towing venture, I had occasional detonation on the way, developing into almost constant detonation on the return trip at or around 2500RPM - Also, the headers glowed red at one gas stop (air/fuel ratio?), and the truck belches oil (like it was dripping from the front of the tow dolly whenever I stopped).

I would run through a tank of gas in 100 miles. I reduced the avg speed from 75 to 50 and got 200 miles out of the next tank, but the detonation was still a problem!

Am I looking for a new motor at this point??

Is this a really bad timing chain issue?
Clogged cat?
Advice?

I am new to domestic V8's (familiar with 4cyl turbo Porsches) and am still getting to know my way around in there.

Any insight will be appreciated!

 

I would look at timeing first. Then the cat. It sounds like ther is a timming prob to me. But the oil thing it not good. Look to see if the pcv valve is good also. Might be not working and building to much presure in the base and blowing oil out a seal.

clipper

 

For whatever its worth I would also start looking for a vacuum leak, somewhere.

Good Luck

 

If your headers are glowing red (and this is not a turbocharged truck ..grin..) then your timing is way advanced, you're running way to rich (and fuel is burning in the headers), or you're sitting at WOT most of the time.

Detonation is caused by too much timing advance, incorrect spark plug temperature, poor choice in gasoline (up the octane), EFI or Carb running waaaaaaay to rich (check o2, all sensors, etc) and possibly spark plug wires misrouted, though the latter is unlikely if the truck idles well.

You're only looking at a new motor if from all this detonation you've burnt your valves or blown holes in the pistons, which is what extreme detonation can do. If it idles well, you haven't blown holes in the pistons yet.

Timing chain could have jumped, though on the 302 they usually stretch a little (not too bad) then snap if they are going to go. I don't believe the 302 in the year range we are talking about had plastic gears, but I've been wrong before.

Thats okay, no problem at all, welcome aboard. And quite honestly, there is very little difference between a porsche 4xyl turbo and an 302 Ford engine, from a troubleshooting perspective. Detonation is detonation, and parts are parts. How you get the engine part and such of course is significantly different, but you knew that ..grin..

 

BTW, if you're belching oil (sorry I missed that tidbit) check the PCV valve(s) and make sure they don't pass oil the wrong way. They might be installed backwards, or simply dead.

Might also be headgaskets. What do your plugs look like? Oily? Black/brown soot? Burnt? Melted?

Oil (and rad fluid) through the exhaust will kill the cat very quickly, along wiith the o2 sensor which just makes the problem worse (ford efi tends to default to rich rather than lean).

Hope that helps...

 

One note on the above, detonation is more likely when the mixture goes lean. Sounds like that could be a possibility here. Exhaust gas temps will be hotter with a lean mixture as well. Converter temperature will be hotter if the mixture goes rich. I would check fuel pressure, and if the truck is computer controlled, I would definitely check to see if there are any codes, and check the timing.

 

I was assuming a LEAN condition also. - which is weird, as it uses COPIOUS amounts of gas!

How do you pull codes on this thing? I have no idea, and no manual just yet...

 

You are correct. I was thinking lean, but typed rich for whatever reason. Can I use the excuse of undercaffienated? My apologies.

 

Poor milage, high exhaust temps, oil out the exhaust sounds like a clogged cat. If the pcv valve were bad, it could send oil to the air box, through the intake and into the chambers to be sent down the exhaust into the cats where it would burn and melt the media inside - you might only be breathing through a third of the available volume of the cat(s). I'd fire it back up and see if they're glowing after a few minutes.

 

If you take the O2 sensor out of the exhaust pipe, then crank the truck, you can get a feel for how much backpressure the converter is creating. Exhaust will really be forced out of the O2 hole if it is clogged. There is also a way to test for a clogged cat using a vacuum guage. I'd definitely get a Haynes manual for your truck - it's a big help. As for pulling the codes, go to this website: http://fordfuelinjection.com/index.htm and click on "Getting Codes" on the left side of the screen. It also has definitions of the codes once you know what they are.

 

Thanks Guys!

I sort of blew off work and wrenched on the truck all day today at the shop. Here is what I've found thusfar:

The timing was at 2degrees BTDC, not 10 (I recently replaced the module - could it caue the change in timing?)

The EGR valve (I am assuming that is what it is, bolted to the intake, with a steel tube attached to it) had a VACUUM LINE MISSING/OPEN.

All the plugs were shot (and showed evidence of heat, of course)

The plug wires were worse than that, an the cap and rotor were bad.

The CV filter was a solid block almost, and the air filter had a layer of asphalt on the bottom of it.


I am assuming the timing and EGR leak were principal causes in the detonation issue. As to the outrageous fuel usage (even with the 3.93LSD, IIRC) and the oil consumption, I don't know, but one thing at a time, right?

I also backflushed all the mud out of the cooling system for a good hour and replaced several hoses while I was in there.

I will give a running report after I return from the 24 hour race in Daytona.

Keep the tech coming, I am determined to get this truck straightened out!

 

Retarded timing can cause increased exhaust temperatures too. It won't cause pinging unless it is out of phase (rotor pointing at the wrong cylinder). I thought about going to the 24 hours at Daytona, but it doesn't look like I'm going to make it. Pull for the Crawford prototypes for me, I know a couple engineers who worked on those cars, as well as Max and Jan Crawford.

 

Red...your hot condition is due to the loose EGR vacuum line, I can almost guarantee it. If it's stuck in the open position, exhaust gases are constantly flowing into the cylinders, leading to detonation.

 

^ Wouldn't that keep it from pinging? That's what EGR is designed to do - reduce combustion temps....

 

OOh how can I get a confirmation on the EGR functioning?

BTW, I have to root for the team I'm crewing on, sorry, LOL.