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Discussion Starter · #1 ·
Let me start by saying i searched and did most everything I found before I posted on here.

Truck is a 91 Ford Bronco 5.0 V8 w/ E40D Transmission.

Problem: Random hesitation/misfire when taking off from a stop, or while in 3rd or 4th gear w/ TC Lock Up. Only under 2000 RPMs, above that it seams to run fine. Does it more warm, hardly no problems on cold start up. Did notice if I unplug alternator and run truck on only 12 volts, significantly worse which leads me to think electrical problem. Also I checked the codes and it had nothing stored.

I've looked over the ignition system. Truck has new Motorcraft plugs gapped at .040. New MSD Plug wires. New MSD Cap & Rotor. New MSD Coil. New TPS. Also checked base timing, its about 10 degrees advanced.

The problem is getting worse day by day and so bad I really don't want to drive the truck. My next step was gonna be to check fuel pressure but I dont have a gauge so I'll have to go pick on up. Anyone have any other thoughts?

Thanks for the help guys.
 

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Did you do the work yourself or have a shop do it? I would double check the plug wires, proper routeing, and make sure you or whoever did the work did not put a gob of di-electric grease in the boots.
 

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Discussion Starter · #3 ·
Did you do the work yourself or have a shop do it? I would double check the plug wires, proper routeing, and make sure you or whoever did the work did not put a gob of di-electric grease in the boots.
I replaced everything myself. Everything was done properly.
 

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If your BKO is an EFI, "pull codes" and see what it's doing first. There are numerous threads on "how to" or refer to your Haynes Manual. :doh0715:

Any chance your plug wires are out of sequence?
Vacuum leak etc.
:banghead

Codes and diagnostics first, "search" for similiarites etc. ~

Good Luck ~ :thumbup
 

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Discussion Starter · #5 ·
I checked for vacuum leaks with carb cleaner, none found. Plug wires are all good, had the problem before the plug wires. It was just time to change them so I did. (100,000 miles)

I rechecked the codes, scanner came up with KOEO- 111 (system pass). CM now had- 327(DPFE or EVP circuit below minimum voltage of 0.2 volts) & 328(EVP circuit below minimum voltage of 0.24 volts).

Its 10:00 here so time to give up for tonight. Any help would be appreciated!
 

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Have you changed your fuel filter? A clogged fuel filter will give you these symptoms. If you haven't changed it for some time or never then think about changing it. You might be surprised. :beer
 

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Satyr of the Midwest
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Just for giggles, disconnect the EVP and see how it runs. It WILL turn the check engine light on, but the PCM will stop EGR flow completely since it has no idea where the EGR valve pintle is. This will give you some more help tracking down whether the driveability issue is directly related to the EVP code. After that's determined, which should take all of about 10 minutes, I would diagnose the EVP by unbolting it, turning on the key, and backprobing the EVP line while moving the plunger tip in and out. You should see a LINEAR voltage increase, proportional to how far you're pushing the plunger in.
 

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Just another suggestion, I always have trouble gapping my pluggs above .38 on stock coils in both my fords. 89 bronco and 97 escort with distributerless. If nothing else works, try re gapping.
 

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Discussion Starter · #9 ·
Changed the fuel filter, No change.

Unplugged the EVP, No change.

Disconnected Vacuum from EGR, No Change.

Rechecked spark plug gap, looks good. Old plugs were gapped out even farther than the new and it made no difference.

Had a good MAP Sensor so Swapped it, No change.

Check Exhaust Back Pressure, Everything looked good there.

Check fuel pressure.
KOEO - 35 PSI
KOER - 28 PSI (thats a little lower than specs but not bad enough for this I wouldn't think...)

I'm about at a loss here, i'm thinkin about putting a fuel pump on just to bring the number back into the correct specs but really dont see it doing any good.
 

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Satyr of the Midwest
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That is low enough to cause problems.

I would probably test/replace the regulator first, though.
 

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Discussion Starter · #11 ·
Yeah But wouldnt low fuel pressure cause a problem on the top on end RPM? I have no problem there, only off idle to 2000. Just asking.
 

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The injectors depend a lot on pressure to establish a spray pattern. if the pressure is low, the pattern is not even and will cause low speed problems too.
 

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Discussion Starter · #13 ·
Well got it figured out. Did a compression check, 35 Pounds of compression on the #2 cylinder. Also getting cylinder blow by through the intake (guess what valve is the problem! Haha. No matter what kind of electronic tests I try, not gonna change that! Haha. Thanks for the help guys.
 
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