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post #1 of (permalink) Old 05-08-2000, 10:41 AM
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Bronco still surging, help!

Hi all, well my Bronco ('88, 351) is still surging, sporadically, after it reaches operating temp. (normally after I come off the freeway and start city driving). I changed the 1) Throttle Position Sensor, 2) EGR (both), 3) Air Charger Sensor, 4) Oxygen Sensor, 5) Air Bypass Valve, and lastly 6) the Fuel Pressure Regulator. Also had a tune up with new wires. What can I do next to try to fix this problem? By the way Don I adjusted the "toe" in the front and I noticed the front tires are wearing more evenly. Thanks....
AAM

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post #2 of (permalink) Old 05-08-2000, 11:24 AM
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Re: Bronco still surging, help!

I hate to ask, but how is your PCV valve? A blocked, or partially blocked valve will give you some surging. Another thought is that your intake could be plugged at the PCV location. Someone posted that idea a year ago or so, and it helped me get rid of a pesky surge I had.

post #3 of (permalink) Old 05-08-2000, 02:25 PM
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Re: Bronco still surging, help!

Hi Ron, I did change the PCV a while back, but it may need another one. Although I remember the vehicle acting up afterwards. Is there a quick check to see if the PCV system is working and/or blocked at that location? I don't want to stick a wire in and regret it afterwards. Thanks,
AAM

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post #4 of (permalink) Old 05-08-2000, 07:16 PM
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Re: Bronco still surging, help!

The manifold should have a baffle between it, and the lifter valley. I would think that if you were careful, you could snake something in there without damaging anything. When you buy a PCV valve, make sure it is made for your engine. If you get one that isn't calibrated for your engines vacuum, you can have problems as well.

post #5 of (permalink) Old 05-08-2000, 09:55 PM
 
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Re: Bronco still surging, help!

I had the same problem with my 351 88. It was my Fuel Pressure Regulator. You mentioned that you already replaced yours, but did you check the fuel pressure? That's how I finally isolated my problem. I could be some other fuel system problem, so checking the fuel pressure may be a good idea. Good luck.

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post #6 of (permalink) Old 05-09-2000, 10:44 AM
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Re: Bronco still surging, help!

Ron, I check the PCV valve and it looks like it needs replacement. I shook it and the valve rattled like it's suppose to. I also placed my finger on the intake portion of the connection and vacuum was impressive. So I assume it's working. I'll change the PCV this weekend and see what happens. Thanks.

Broncoloco, I haven't checked the fuel pressure becasue I don't have a gauge. I guess it's time to invest in one. I did check the injectors with a stethoscope and they seem to be working (hissing without a miss). I am having problems with the sending unit on the fuel pump and haven't replaced the pump because it's working. Thanks...

Guys, I haven't changed the BAP sensor and don't know if my '88 has a MAP sensor. Could any one of these two sensors cause the engine to surge, sporadically (when warm)?

post #7 of (permalink) Old 05-09-2000, 11:58 AM
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Re: Bronco still surging, help!

When you say surging.....do you mean SURGING......or just an intermintent annoying mild surge? When this occured for me it end up being a gell-like deposit in the hose to the MAP sensor that caused it to malfunction. Another problem that I had caused the engine to buck momentarily for no good damn reason......hot, cold, high speed, slow high gear, accellerating (you get the idea). It ended up being a bad connector on one of the sensors to the intake (I forget which one).......I had to get a premier menchanic (at the time) to check it out and he finally did a "wiggle test". This is where the Megabuck Sun machine is hooked up (there are now many far cheaper hand helds that do the same test) to the engine and you wiggle all the connections. It beeps when you find the faulty hookup. In my case it was a cracked connector.

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post #8 of (permalink) Old 05-09-2000, 07:13 PM
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Re: Bronco still surging, help!

On my '96 with the 351, I had a surge when I would just crack the throttle open, then sometimes I had a rough idle. It turned out that it was the EGR valve opening to soon, because vaccum from the EGR seloniod was making it. What I am saying is I replaced the EGR seleniod and all problems where gone.

post #9 of (permalink) Old 05-09-2000, 07:59 PM
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Re: Bronco still surging, help!

Gary, yes, it is an intermittent annoying mild surge, only when it's warm. My next step was to replace the MAP and/or BAP sensors depending on the feedback I received from these posts. I haven't considered a loose connection, anything is possible. But that would be a tough one to find. Thanks.
AAM

post #10 of (permalink) Old 05-12-2000, 12:50 AM
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Re: Bronco still surging, help!

Is your TP sensor adjustable? If so, what voltage did you adjust your TP sensor to? The correct settiong should be between .96 and .98 volts. This number can be obtained by backprobing the green and black wires on the sensor and taking the reading with a digital volt meter. Have you run codes yet? If so what codes did you get?

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