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351 bogs under load/acceleration

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  #1  
Old 07-28-2017, 10:02 AM
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Unhappy 351 bogs under load/acceleration

Alright, looking for some direction! 1995 Bronco, 5.8L. I haven't driven the truck much in the past year, and a new issue has risen. This started towards the end of it being a daily driver, so my first thought isn't old gas.

The truck will idle fine and will even rev when in park. Once I take it out to drive it's a different story. I can put it in gear and idle around all day, but once I give it some gas to accelerate it bogs down and wants to stall.

I ran codes, got an EGR code and went ahead and replaced the valve (and the subsequently broken tube connecting to the manifold which was fun!). I also replaced the coil.

I figured this was a fuel supply issue, but just tested pressure at the rail and am seeing constant 29psi at idle and 39psi when I remove the vacuum line from the fuel pressure regulator. Also jumps to 39psi when I hit the throttle, but backs down to 30 if I hold the RPMs up.

Next thought is TPS or IAC, but wanted to check for any advice before throwing more parts at it. Not getting any additional codes either...

Thanks!
 
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Old 07-28-2017, 10:33 AM
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when was the last time the fuel filter was replaced. the pressures you listed are good but don't indicate volume available.

could be dirty injectors or gummed up from lack of use. might add some stabilize and let it run for a half hour in the driveway.
 
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Old 07-28-2017, 10:37 AM
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I did replace the fuel filter the other week when I started messing with it again. I'm fearful that part of the issue might be a gummed up pump, but of course I'm hoping its something else as to not have to drop the tank! Any way to test the volume? I'll pick up and run some stabilizer in it. Thanks!
 
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Old 07-28-2017, 12:51 PM
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Are you getting any codes now are those repairs?
 
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Old 07-30-2017, 12:10 PM
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Originally Posted by Conanski View Post
Are you getting any codes now are those repairs?
I haven't had a chance to test again, but will try to soon.

What's frustrating also is that I can't get any consistency on the problem. I mas moving cars around yesterday and I drove it around the block with zero issues, and then a few hours later did the same and the problem had returned. Both trips were in the afternoon with 100+ temps so there wasn't any big variations in conditions between the drives.
 
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Old 08-02-2017, 03:08 PM
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you may have a bad tfi module or issue with the distributor pip sensor.

timing at 10*btdc with spout removed?
checked for any vacuum leaks?

sounds like the timing may not be advancing when under a load which points to the dizzy
 
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Old 03-03-2018, 02:44 PM
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Same problems here. F150 92
Also vibrations at various speeds. Thinking it's a timing issue.?
 
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Old 06-07-2018, 01:15 AM
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So life took over for some time and the Bronco had to hibernate in the garage.. but I'm back at it now. I finally got the truck inspected, registered, and limping on the road. I was hoping that some driving could show me patterns for temperatures, driving conditions, etc. to help narrow down the problem, but no luck. It remained quite random.

Kemicalburns- based on your comment and so many threads with the exact symptoms, I went ahead and replaced a number of parts, including both the TFI and distributor. I figure at this Bronco's age I don't find putting some fresh parts on. There were many others I tried, as well.

I hope I have finally reached the problem. I pulled the PCM tonight to check out if it had any water damage, as I previously had a leaky front windshield. No water damage detected, but I do think it has the leaking capacitor issue. I have no idea what I'm looking at other than "these capacitors have black stuff at the base that others don't." With that, could this be the issue? And if so, does anyone have a good recommendation for a vendor to purchase a replacement? I see a few used ones online and then the online stores who will sell the units flashed for your VIN. With very little tech knowledge I'm not sure how good those sources are?

Please be the problem...

 
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Old 06-07-2018, 07:41 AM
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That is definitely a big contributor to your issues. Take a photo of the alpha-numerics/numbers on your current computer (PCM). The key numbers to look and use for locating a replacement is something like F5TZ-12A650-YB. Omit the center 12A650, just use F5TZ-YB. The center 12A650 is the base part number for all PCMs so your search results will increase exponentially. F5TZ-YB is listed for a 1995 Bronco/5.8L/E4OD with Federal Emissions. F5TZ-AAA and F5TZ-AAB are for California emission Broncos. I believe the AAB is a later revision AAA.

Where to find a good replacement is a crap shoot these days. No one makes new ones (and no one can "flash" this vintage PCM). Most parts houses sell rebuilt units from Cardone, which is the absolute worst IMHO.
 
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Old 06-15-2018, 09:20 PM
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Thanks Randy. I found a replacement Ford unit and popped it in. Interesting results as the symptoms that I have had still seem to be there, but way less prominent. Almost as if now the truck is just powering through it.

The noticeable symptoms still happening are slight hesitation/bogging at take-off (at times) and then when cruising at highway speeds the tach will jump around ~200-300 RPM. The tach jumps aren't noticeable in power or engine sound. Could any of this be tranny related?

Just finished up running codes - both KOEO and KOER came back with no codes. Prior to the PCM replacement I was getting a code for the EGR sensor and O2 sensor running rich. These are gone and I have not had the check engine light again.

Thanks for everyone's help!
 
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