Efi bogging on 87 octane

[hammer]

Hey guys,

Ford maf efi 5.0l. Explorer block, mustang heads and intakes.

Been having an issue of bogging under load. I needed a new coil last August due to weak spark. During that time I screwed around with the distributer. Reset the timing to 10 btdc. Went for a drive, bogging under load. Try 12 degrees. Same thing. Try 14 degrees. Worse. Put it back to 10.
I chalked it up to it being really hot out and my intake pulls air from the engine compartment. Just on a whim I decide to try higher octane fuel, see what happens. Bronco runs much better. Still not gonna a win a drag race but it's driveable again. So I run 91 the rest of summer.
Go to fill up for the first time this fall and put 89 in it. Figured the hot outside temp won't be a factor anymore. Bronco falls on its face. Bogging worse than ever all through 3rd and 4th. On my way home I squeeze 1/3rd of a tank of 91 in and buy a bottle of octane booster. Truck runs mint.

Engine compression is 150 on all holes. Fuel pressure is good at the rail.

Where's my problem?

 

[73azbronco]

All things equal, Bogging can be just as much a gearing issue as anything else.

150 all cylinders wet/dry? 100psi is supposedly minimum for an explorer motor but I like 170-180 myself...

You have good pressure, do you have good Fuel flow/volume? Filter? Old gas in tank maybe?

If it is truly an octane issue, is it a stock motor with stock camshaft?

What do your plugs look like?

Is it just bogging or is there pre ignition/knocking when it boggs?

 

[bmc69]

Does your engine run the knock sensor?

 

[spap]

when did the bogging start, after you added everything. Or just all of a sudden
Is the timing advancing??? gear and tires info helps too, I think changing octane you might hear pinging but not really cause a bog.
plus what was said already

 

[hammer]

150 all cylinders wet/dry?

You have good pressure, do you have good Fuel flow/volume? Filter? Old gas in tank maybe?

If it is truly an octane issue, is it a stock motor with stock camshaft?

What do your plugs look like?

Is it just bogging or is there pre ignition/knocking when it boggs?

- I don't know for sure what wet/dry means. I'm assuming your asking if I disconnected the fuel when I did a comp test. I did.
- if I had a fuel flow problem, how would different octane make a difference?
- fuel filter before the pump at the tank is new. Filter on my accumulator is 7 years old.
- gas is days old. Driven 150 miles in the last two days.
- stock motor. Stock cam.
- no knocking

 

[hammer]

Does your engine run the knock sensor?

I don't believe so. I don't think any explorer blocks had them but I may be wrong. If I did it would be at the back of the block behind the intake manifold correct? If so I don't have one.

 

[hammer]

when did the bogging start, after you added everything. Or just all of a sudden
Is the timing advancing??? gear and tires info helps too, I think changing octane you might hear pinging but not really cause a bog.
plus what was said already

Bogging started after the truck died on me due to the coil not producing enough spark. Went from an accel coil back to stock.

I'll check the timing again today. But like I said, I tried 10/12/14 and then went back to 10.

513 gears on 37's. Zf5.

 

[spap]

When you went to the ac coil did you open up the plug gaps, and then went you went back to stock did you reduce the gap. Stock is only like .26
Sorry just kinda of reaching to help.
Throw I
A trimming light on it to eliminate any timing advance issues I know you set the timing but use the timing light and rev the motor up a bit to make its advancing the timing off of the crank pulley I would make 20 25 30 degrees just so you can see it advance

 

[Jdgephar]

Just thinking out loud...or on paper...e-paper...

I don't know much about your engine build (cam degree to crank, etc.) Higher octane just slows down the burn and the ignition of the fuel. Timing marks may be slightly off on your dampener as well. Did you try running at 8 or 6 degrees advance? It could still be a simple as too much advance.

Might also try a reset of the computer (just unplug the battery) and let it re-learn.

 

[Joe473]

- I don't know for sure what wet/dry means. I'm assuming your asking if I disconnected the fuel when I did a comp test. I did.
- if I had a fuel flow problem, how would different octane make a difference?
- fuel filter before the pump at the tank is new. Filter on my accumulator is 7 years old.
- gas is days old. Driven 150 miles in the last two days.
- stock motor. Stock cam.
- no knocking

Check the rubber ring on the damper and make sure it didn't spin. This would act like a timing issue and most likely cause.

Also how old are the plug wires and is there separation on them. The late mustangs and explorers were good for crossfiring under load.through the plug wires when they started getting old. I know higher octane shouldn't help this but they did it intermittentently.

Sent from my SM-G900V using Tapatalk

 

[73azbronco]

Well, if it all happened right at the coil failure, you most likely have an ignition based issue.

You note it runs perfect with high octane. However to me that means mechanical issue/compression/timing.

Has it ever run poorly with high octane? Never????

I asked about fuel pressure and flow because that is a basic starting point to ensure you are not missing something simple and cheap. Many people never check flow. I asked about wet or dry as in a wet compression check or a dry compression check, I bet you did a dry one, as your number suggest, nothing wrong with that.

So, what type ignition, how new?

Battery voltage good?

My gut feeling is you have a bad ground. Also, since you blew a coil and played with dizzy, might have fried the dizzy rotor or cap/coil wire or plug wire. But if it truly is octane dependant, you could have carbon build up, exhaust backpressure, computer issue, ground to computer issue, wire issue to O2 sensor or faulty O2 sensor.

Think back to when it was running good, and what you did in between then and now.

 

[hucklburry rev2]

do you have the spout connector in the distributor wiring and did you pull it when you set timing?

 

[73azbronco]

any word?

 

[hucklburry rev2]

any word?

I know, I'm just curious, cause if he didn't pull the spout to set timing, its way off and an easy fix.

 

[edmedlin]

Since it all started after the change in the ignition, that is where I would start. You will probably find that your gas mileage is going downhill too. A weak spark will show up more at lower rpms.

 

[hammer]

I disconnected the spout connector when I set the timing

 

[73azbronco]

so where are you on this?

 

[hammer]

Still got a tank of 91 in it. Running great!

Next fill up I'll put 87 in and take it from there. Not much sense troubleshooting the issue when there is no issue.