Running rough and missing

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Jun 19, 2022 | 04:26 AM

88f2fitty

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5th Gear

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Running rough and missing

I have a 1988 F250 that is was running great after changing all the plugs wires cap and rotor but then I towed my new camper (20 foot bumper pull) from airway heights to post falls which is about 40 miles. It was running real rough and missing and died on its own. The plugs were all fouled bad so I changed just to the plugs to a highly recomended plug (motorcraft) and it ran great again but the only driving I did was to Kingston with my camper another 40 miles. And it’s doing the same thing just not as bad. I did a dump run today without much weight in the back just an old 4.0 motor and trans and some household garbage. Also about 30 miles round trip. It seems to be doing better after that but not by much. Any ideas on what’s going on would be helpful.

Jun 19, 2022 | 06:49 AM

My4Fordtrucks

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Remove the vacuum line off the fuel pressure regulator to see if the diaphragm is broken allowing unmetered fuel to be drawn into the intake manifold.

Jun 20, 2022 | 07:42 AM

88f2fitty

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I didn’t think of that. I’ll check it when I get home tonight and give an update, thank you

Jun 28, 2022 | 01:38 AM

88f2fitty

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I checked it finally without rubbing it first and there wasn’t moisture but when I get a chance I will start it for a bit then check.

Jun 30, 2022 | 06:16 PM

88f2fitty

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Still no moisture after running it pretty hard for about 20 minutes, any other ideas?

Jun 30, 2022 | 06:24 PM

torq'ta 5 8

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From: N.W. Alabama

What engine, 02 sensor still plugged in, codes, even if CEL isnt on?

Jun 30, 2022 | 06:25 PM

rla2005

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From: Kentucky

One of the most common failures of the pressure regulator is a ruptured diaphragm as stated before. Since you are not seeing any fuel leaking the next step is to verify the fuel pressure at idle, idle with the vacuum line removed, then under load.

Fuel pressure at idle should be 30-32 PSI. At idle vacuum line removed should be ~40 PSI. Under load, vacuum line attached, should also increase to 40 PSI range. As the load increases the manifold vacuum lowers which in turn increases fuel pressure.