Stumbling Bronco

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DanL

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I have or should I say my son has my 1996 Bronco 5.8 ltr. EB, Great truck, Beautiful Spotless inside, and out. I bought the truck new in 96 gave it my father-in-law 2001 with 98,000 miles, dad in-law past 2012. The truck sat up for a year, and my son became the new owner at 118,000 miles and it currently has 150,000 miles.

    My issued started when you would drive a while and the truck was at operating temperature and shut it off and for a few minutes and go to start it up again and it sounded like the worst case of stumbling, misfiring and would shut back down. Sometimes if you patted the gas as it was stumbling, it would finally level off and run, other times it would not start at all, you would have to let it cool off before it would start. The check engine light was on and OBD codes were the lean 171, and 174 I can’t seem to get rid of them since regaining gaining possession of the truck.

The last OBD codes that came up were PO385, PO174, PO 171. I have replaced most all of the sensors including O2’s, Crankshaft Position Sensor “before the PO385” code came up and cleaned Mas Air flow sensor today. Have about 25 + in. vacuum, changed the fuel filter, 32 lbs. fuel pressure. I rechecked Crankshaft Position Sensor the wires were twisted and I unplugged it rotated it to get the kinks out and the wires did not seem to be damaged or broken. I did not drive it after I working on it today, I let it idle for a good hour, and it idled well, crank and started up without any issues. The truck runs fine most of the time, any thoughts what I should be looking or testing next. Maybe a smoke test on the complete vacuum system.

 

miesk5

96 Bronco 5.0
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Yo Dan,

Welcome!

Fuel pressure with engine running should be 28—45 PSI.

Depends on gauge accuracy, but that is OK.

With key on and engine not running, 35—45 PSI.

Check plug wire routing, should be the VECI DECAL atop radiator support.

Or,

&

The firing order for 1994 through 96 5.0Ls & all 5.8Ls is 1-3-7-2-6-5-4-8. On these vehicles the #1 and #3, or #5 and #6 spark plug wires must be separated to eliminate the possibility of an induction crossfire. To eliminate the possibility of the coil wire becoming disconnected, route the coil wire under the spark plug wires at the distributor cap.

sparkwireroute94-up_5l.jpg

...

PO171 & PO174, see my very recent pin-point test here @ http://broncozone.com/topic/25484-codes-p0171-p0174-running-lean/

Can start with the vacuum leak test. It is in that thread. Beg, borrow a vacuum gauge from local parts store under a loan a tool program, or buy one...

Normal Engine Vacuum in a 96 Bronco at Idle is 15-22 in-Hg.

...

PO385 see my test @ http://broncozone.com/topic/24629-engine-stalls-when-put-in-reverse/

...

next time, please fill out Signature with year, engine/tranny/Xfer case/hub type info & major mods such as a Lift, etc. for better responses.

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