PLEASE HELP 1990 with a 302 EFI

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Robert Ashby

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Hello,

We have performed a frame off restoration on a 1990 Bronco, everything was moving along well up until we tried to start the engine for the 1st time. 

The engine will start then cut right off, then we restart it and it will idle once it warms up. We have changed everything twice, even the wiring harness for the injectors. New computer, new distributor, new MAP sensor, TPS sensor and everything else we could think of. It will idle well but once you hit the throttle and release it, it runs rough and wants to cut off.

Has anyone run into anything like this??

 

BMAD01

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Sounds like a nice project Robert!  If it runs, I'd be pulling codes to see what is causing the problem and go from there.  Good luck!

 

miesk5

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Yo Robert,

As BMAD01 advised, try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19

http://broncozone.co...7&mode=threaded

The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.

Run it around to heat the engine up and shift thru all gears including Reverse.
Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch.
Then turn off engine, all accessories/lights (close driver's door) , etc.

Do KOEO test First. Post Code(s) here according to KOEO
& KOER.

A helper can assist you by counting the codes. Some use their smart phones to record them.
BEWARE OF FAN, BELTS, PULLEYS, HOT HOSES, IGNITION HIGH TENSION WIRES, AND ENGINE COMPONENTS


 

miesk5

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Yo,

Had to re-boot.

Some no code usual suspects by Ford;
▪Vacuum leak; See  my vacuum leak test in post #20 @ http://broncozone.com/topic/23994-90-58l-getting-continuous-code-33-and-running-code-44/?p=125535


One way to do a quick check is to grab a vacuum gauge. Bring the engine to normal operating temperature. Connect gauge to the intake manifold tee. BEWARE OF FAN, BELT, PULLEYS & HIT ENGINE. 

The vacuum gauge should read between 15 and 22 in-Hg depending upon the engine condition and the altitude at which the test is performed. SUBTRACT ONE INCH FROM THE SPECIFIED READING FOR EVERY 1,000 FEET OF ELEVATION ABOVE SEA LEVEL.
The reading should be quite steady. .

When engine is rapidly accelerated (dotted needle), needle will drop to a low (not to zero) reading. When throttle is suddenly released, the needle will snap back up to a higher than normal figure.


Fuel quality; Oxidized fuel often turns darker over time and may even smell sour. You can check stored gasoline by pouring some into a clear glass container and comparing it side-by-side with known fresh gasoline. If your old sample looks noticeably darker than the fresh gas, you have strong evidence the gas has gone bad.

 
OP
OP
R

Robert Ashby

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Thank you for the responses, a little more background on this Bronco.

We had the engine completely redone stock, and we have inspected every inch and plug on the engine wiring harness. We have replaced every single sensor in the engine system twice, as well as a new computer (EEC). New injectors and a new distributor, we even changed the fuel pump again. We have perfect vacuum pressure per the specs. 

After we changed the fuel pump we checked the fuel pressure with the vacuum controlled fuel pressure regulator hooked up and we have 30psi, when we take the vacuum line off of the FPR the fuel pressure jumped to 40psi and the engine runs perfectly. So we plugged the vacuum line left it off of the FPR and test drove the bronco. It runs better than it ever has since we have installed the motor and performed the restoration. 

We came back and hooked the FPR back up and sure enough, it runs rough, we replaced the FPR with another new one and it does the same thing. Runs better without the FPR hooked up at all. We have the computer diagnostics equipment to read OBD1 and we have no codes. I'm baffled, but I am a much better truck mechanic than I am an engine guy.

Any insights would be much appreciated!

Ashby's Inc. / Crenshaw Corp. on facebook to see pictures of the Bronco

 

miesk5

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Yo,

Pinch or block the fuel return line temporarily to see if pressure goes up. If it does, it means the regulator needs to be replaced. If there is no change, the problem is a weak fuel pump or a restriction in the fuel line such as a plugged fuel filter.

 
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The items I've had cause this at various times:

Plastic vacuum lines going to EFI manifolds (Rough idle, Cruise failure, other random issues ) [ All were cracked due to age/material/location. Break all lines up to 1" of connections and replace line with rubber hose ]
02 Sensor (Brand new one but I sprayed it with Carb Cleaner so Out Of Box I fried it, replacement did fix all hill climbing issues)
TPS Sensor (Rough idle and general power throughout)
EGR Valve (Rough idle and general power throughout)
Fuel Pump In Tank and On Frame (Rough idle, loud noises, then finally no more go)
Fuel Accumulator/Resevoir [Just before On Frame Fuel Pump] (Hill climbs, rough idle, fuel spraying all over the place. This was the most recent item to fail)

What should be notable is that each one had it's own "Rough idle" issue ;)

 

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