Major detonation/power loss issues '95 F-150

[Diabolic]

Timing has nothing to do with AFR. Leave it at 10 degrees.

 

[needmorepower]

Timing has nothing to do with AFR. Leave it at 10 degrees.

I can't. It detonates.

 

[Briansshop]

Have you checked the amount of full timing advance with a light?

 

[needmorepower]

I have not. How does one do such a thing?

 

[Briansshop]

Run the rpm up while watching the timing at the damper. You might want to highlight 20*,30* to make them easier to see and have something to go by.

 

[needmorepower]

Run the rpm up while watching the timing at the damper. You might want to highlight 20*,30* to make them easier to see and have something to go by.

I do that with the spout in, correct?

And do you know the thread size for the schrader valve by chance?

 

[Diabolic]

Since we are trying to see what the AFR looks like under load on the wideband......just set the base timing at 10 and test with the spout out. If the AFR looks good, set it at 15, then at 20, then at 25. Leave the spout out for AFR testing.

 

[needmorepower]

Got it.

 

[SA94Lightning]

Best way is with an advance-able light. Lets you set degrees advance at idle.
Like this
https://www.amazon.com/dp/B000EVYH7W/?tag=aymo-20


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[needmorepower]

Alright, I hooked up the wideband. And before you look at this data, it's important to note that this '95 truck is a California emissions (maf with dual O2's) vehicle and based on some afr observations I did right after putting the engine back together due to the head rebuilding, after which the truck was running great, it appeared Ford programmed these things to pull a ton of fuel and timing down in the lower rpm's to comply with emissions. Basically, anything under about 2,500 rpm, the afr stays steady at 14.6-8 even at wot. It doesn't start to richen and pick up power until some time after 2,500 rpm, at which point it will go into the mid-low 12's as rpm's climb over 3,000 and it then pulls like it did when it was still speed density several years ago. But in the lower rpm's the California emissions trucks stay around 14.7 afr and that is normal, so keep that in mind. However, the truck currently is extremely powerless at all throttle positions under load. I can do 80 mph on flat ground just driving casually, but at wot I can't get over 30 mph as you'll see in the video below.

I put the wideband sensor into the now-unused original O2 sensor bung in the crossover pipe before the cats. If necessary I can put it into each bank seperately.

Anyway, here's what I observed.

Base timing set to 10, spout IN.
At wot and above 2,500 rpm, the afr went down into the mid to low 12's and it detonated while in the 12's. This was the only time that I tried it with the spout IN.

I then removed the spout and drove with it at 10, 15, 20 and 25 degrees base timing. It seemed to run best at 15 and 20, but that's a relative term because it was still as gutless as can be, just a little peppier maybe. It never ran lean, aside from an occasional 15.X afr at throttle tip in or decel. Casual driving the afr stayed around 14.7 until about 2500 rpm, as I had observed when the truck was running great after the engine reassembly, and then it would fatten up, but sometimes didn't get fatter than 13's. Other times it went into the 12's.

While the spout was removed I did not hear any detonation, not even at 25 degrees. This video was taken when it was at 25 degrees base timing with spout out.

https://youtu.be/yp48RTFGmtI

 

[Briansshop]

The method I suggested should be done with the spout in so you can check/confirm the commanded timing.

 

[needmorepower]

The method I suggested should be done with the spout in so you can check/confirm the commanded timing.

Will it fully advance the timing at higher rpm's without being under load?

 

[needmorepower]

Ok, I just tried it. It advanced timing to either 26 or 28 degrees. I couldn't quite tell which one.

 

[Diabolic]

So it sounds like the advance works and the AFR "average" is in check. I'm sorry. It I may have missed if you replaced the cats or not. Could they be clogged? Have you verified compression in all 8 holes?

 

[lightning_2000]

I'm thinking it's the cats to

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[Diabolic]

Ok, I see you did a compression test. I'm going with cats.

 

[lightning_2000]

Pal put a aftermarket set on his 04 silverado. They didn't last long. It was way down on power. Barely pull hills

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[needmorepower]

I did recently check compression and it was at 150+ on all cylinders and it doesn't burn oil. The cats could be clogged. That was one of my earlier thoughts. I was going to uncork the two spare O2 bungs I have and see if that made any difference but I forgot about it. I will try that next. They shouldn't be though. They're only about 3 years old. Not sure on the mileage. Maybe 60,000.

- - - Updated - - -

Pal put a aftermarket set on his 04 silverado. They didn't last long. It was way down on power. Barely pull hills

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I'm crossing my fingers that that's it then. It has definitely been a gradual decrease in power over the course of months, and cats would do that, and they are aftermarket.

 

[Briansshop]

Cats make sense since everything else is coming up normal.

 

[needmorepower]

SON OF A B!!!!!!!

I unplugged the two O2 bungs and went for a drive and it revved past 4,000 and kept pulling!!! Unbelievable. What kind of $hitty cats plug up that fast? Anybody know of a decent brand that won't break the bank?

And thanks for all of the troubleshooting knowledge and suggestions, guys. This original 351W short block should make it all the way to the moon and back now. Only 62,716 miles to go (currently about 414,500)!