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87 2.3 5sp 4x2 random acceleration


MikeW

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Hi gang!
Years ago you all helped me get this little 87 2.3 5sp 4x2 with the pcm issue running again which has now been problem free for over 10 years. TYVM!
But now I call on you once again with a troublesome little problem.
In the last few days I've experienced a new issue. Random acceleration. It's not excessive like 90 100 mph...but it's enough to make your BH pucker and the brakes don't work well when it happens either.
I suspect that the tps may need some attention, or perhaps the map sensor?
here's the breakdown for those of you who love our Rangers and can't resist a challenge =D

**NO KOEO/KOER CODES** Always the first thing I do. =D

What I know:
About 3 weeks ago, it started running a little rough, presented with power loss at take off, occasional stuttering at cruise speed with lights dimming, foul smell.. not eggs like a cat, more like burning grease (but only with headlight, heater on simultaneously) and a sizable drop in mpg (18.5 to about 8.25)
Since I only drive it to work and back (about 12 miles a day) and the grocery store once a week I figured I'd wait for a little warmer day to tear into it.

What I've done:
Replaced my fuel filter about 3k ago, plugs, wires cap & rotor less than 2k ago
I have checked the vacuum lines, gaskets and clamps and the like. I've checked electrical component connections and harnesses for obvious damage. Cleaned battery terminals, checked hot/negative cables for damage and solid connections. I've checked the engine grounds, fuses & fuel pump relay. Belt is new, alternator is putting out 13.8-14.0 (3G upgraded 8 years ago)
Sprayed out the TBI, cleaned & lubed throttle linkage on TBI, tapped the TPS, tapped the MAP, tapped the IAC and tapped the DPFE sensor (which for what it's worth used to tick loudly, a lot at acceleration ticktickticktick and is now really quiet although it still ticks)
coolant is good, oil is good, other fluids all good. Been using the same gasoline for 12 years no new changes.

Currently:
One day last week (Dec 27 2016) I was headed to work and it started right up and ran like a top, just like shes always done! in fact... a little too well. My truck has hit 75 before, down hill. with a tail wind. But now... she just zips right up there 70...75...80.... strange behavior, but that wasn't good enough and now since 2 days ago (Dec 30 2016) it's decided that we need to just speed up for no reason whatsoever...5 ... 10...15 mph... then everything returns to normal, ride lasts about 40 seconds or less. While this is happening the brakes are hard to press, feels like increased vacuum in the booster. and a side note, a couple times when I pressed in the clutch to shift, the engine would rev up just enough to make the shift difficult, as soon as I released the clutch everything feels normal again, It's generally about this time you feel the random acceleration, which is a very smooth transition, someone not familiar with the truck may not even notice until you look down and see you're doing 75 and the brakes won't slow you down.
I've seen a LOT in the last 10 years working with Ford but nothing like this. So.... what y'all think?:icon_twisted::icon_confused:
Thanks,
Mike
 
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Rock Auto 5% Discount Code: F9A1A579ACFAD1: October 1st, 2021

Mark_88

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Hi Mike...welcome back...

My first guess would be your accelerator is sticking and/or cruise control is activating on it's own...assuming you have cruise control.

The MAP sensor in my 89 Tempo gave me sporadic erratic idle and actually showed up on the scanner because it affected how much fuel the computer allowed into the mix...so it may affect fuel consumption if bad...but you'd get some hesitation and probably erratic idle...but it would show up somehow typically.

An accelerator would not do that even with the TPS doing feedback because it is within the normal range of operation. These cables can get stuck in the sheathing and jam, but usually it would be like an overnight sitting thing and you'd notice it right away...and it would probably get worse over time.

The accelerator cables are not cheap from what I recall, but you should be able to grab one from a junkyard to test...and you can soak it with penetrating oil by spraying it and working the cable in and out a few dozen times.

It would not affect the fuel consumption though...at least not that much...and it won't enhance the performance so that you go faster faster than normal or beyond the normal range you're used to...so something else may be at play here.

I thought right away that maybe the front brakes were seizing due to the flex lines collapsing where they act like a one-way valve. This caused the brakes to stay on, the smell, the lagging, and other effects fit...as well as fuel economy taking a hit because you are essentially fighting the front brakes all the way...until they release.

You can check if the brakes are seized by feeling the front rims...if they are hot to the touch then your front caliper(s) are being locked...

Other than that...I'm out of ideas...
 
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tomw

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You could have a sticky throttle plate. With low mile trips, they can get gummed with PCV gases fed into the intake.(also coats the inside of the intake, and can make passing an emissions test more difficult). I'd consider removing the air tube from the throttle body, and opening the throttle manually for inspection. If it sticks, your idle will be too high intermittently.
Another item to check is the IAC, Idle Air Control. If it gets gummy, the same thing will/can happen.
One last thing is that the fuel pressure regulator can stick(again, short trips..), and bump your pressure higher than required. If it sticks high, fuel mileage can easily be cut in half. If you have the regulator with the vacuum line attached to the diaphragm, pull it off and take a whiff of its odor. If fuelish, likely a punctured or ruptured diaphragm, allowing fuel to be drawn into the intake via the vacuum line, AND adding higher pressure to the injectors.
tom
 


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