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Hey guys, this may be a rookie question, but I am hoping its simple and a common problem.

I just got a 1994 Bronco, 351w EFI

Sometimes, not all the time, I hit the gas and it just lags, chokes, whatever you want to call it, and doesn't accelerate. After about 2-3 seconds it kicks in and accelerates me. Its an intermittent problem, happens about half the time. The rest of the time accelerates fine. It also seems like after I have it warmed up, 10-15 minutes of driving, it doesn't do it as much.

What could this be? So far I have tried putting new spark plugs in, new fuel filter, fuel system cleaner dumped into the gas tank. Anyone know where I should look next?

Thanks a lot in advance for any help you can give me!
 

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First I'd start by pulling fault codes from the computer and see what elec./electronic fault codes are idicated......for How To.....www.fordfuelinjection.com - has it all

Plugs, fuel filters etc. etc all good but it's throwing money at a problem you don't understand yet..... IAC = idle air control, TPS = throttle position sensor and ECT = engine cooling temperature sensor, O2 sensor = oxygen sensor are basically fuel managers at cold start and normal operation so you need to become familiar with them, how they relate to each other and test for issues should any of them be an issue.
I'd also check/test the FPR = fuel pressure regulator located on the fuel rail, drivers side towards the back, however there are no codes for FPR as it's a vaccum issue so you'll need a fuel pressure guage to test for PSI say 37 psi engine off cranking and 40 psi engine running with the vaccum line disconnected, FPR's run around $23.00 and easily replaced.

Fuel relay switch usualy located in the engine bay sometimes on the drivers side fender/firewall area is a squarish device with 2 wires can play a part if it's an original OEM, not expensive and easy to splice into the harness.

Ignition modules either the TFI = thick film integrated - direct distributor mounted style or remote mounted module style can play an issue but here you can TEST FREE at most auto stores, test several times for passing grade otherwise replace with a Motorcraft.

Same here with ignition "coils"...check test etc. you never know...

Make sure none of the throttle linkage is binding up top at the throttle body, do a visual inspection.....easy peasy!

Haynes Repair Manual or www.broncolinks.com are also excellent DIY sources.

Just some thoughts!

Good Luck ~ :thumbup
 

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pull codes

and check the TPS voltage while sweeping the accelerator open to close.
 

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Discussion Starter #4
First I'd start by pulling fault codes from the computer and see what elec./electronic fault codes are idicated......for How To.....www.fordfuelinjedtion.com - has it all

Plugs, fuel filters etc. etc all good but it's throwing money at a problem you don't understand yet..... IAC = idle air control, TPS = throttle position sensor and ECT = engone cooling temperature sensor with O2 sensor are basically fuel managers at cold start and normal operation so you need to become familiar with them and how to test for issues should any of them be an issue, I'd also check/test the FPR = fuel pressure regulator located on the fuel rail, drivers side towards the back, however however there are no codes for FPR as it's a vaccum issue so you'll need a fuel pressure guage to ets for PSI say 37 psi engine off cranking and 40 psi engine running with the vaccum line disconnected, FPR's run around $23.00 and easily replaced.

Fuel relay switch usualy located in the engie bay sometimes on the drivers side fender/firewall area is a squarish device with 2 wires can play a part if it's an original OEM, not expensive and easy to splice itto the harness.

Igniton modules either the TFI = thick film integrated - direct distributor mounted style or remote mounted module style can play an issue so here you can TEST FREE at most auto stores BUT test several times for oassing grade otherwise repalce with a Motorcraft.

Same here with ignition "coils"...

Make sure none of the throttle linkage is binding up top at the throttle body, do a visual inspection.....easy peasy!

Haynes Repair Manual or www.broncolinks.com are also excelent DIY sources.

Just some thoughts!

Good Luck ~ :thumbup
Thanks a lot man! I will look into those things and see what I can do!
 

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Sorry I mispelled www.fordfuelinjection.com ~ :rofl:

Once you find the problem, in additon:

Using the FSB search tool or www.broncolinks.com .

There is a Ford Racing Performance Parts "idle setting procedure" Instruction Sheet (Techline (800) FORD788) steps 1-9 on How To adjust idle by disconnecting the IAC and drilling out the mounting screw holes on a newer "plug & play" TPS so you can adjust it for voltage setting.

In the past the ideal setting was thought to be .93-.97 volts or just under 1 volt but recently posted information regarding this appears the setting should be between .55v-.75 volts.


Posted by FSB member Jermil01:
Wanted to update this thread based on some TPS adjustment information I got from one of my tuning sites. This goes against the conventional wisdom of setting the TPS closer to .95 range. Thoughts??

Regarding any ECU controlled function (and idling conditions in particular), before any strategy based adjustment can be made by a computer controlled system, it must first run somewhat normally in a default and OL mode.

To do this with a FORD you must first follow a few rules.

You must keep the TPS input above the deadband area and below the "tip in" area. On a FORD this equates to below approximately 0.9V and above 0.45. Anything above 0.90V the ECU thinks the throttle is starting to open. This brings into affect possible dashpot and fuel cut strategies which can turn one grey real fast. Below approx 0.40-0.45V the system suspects an incorrect input and substitutes a default figure.

So first off, the TPS should be set to around 0.55-0.75V.You can also disconnect the IAC then disconnect the battery for 15-20 minutes, reconnect and the computer should default back to factory settings.


Good Luck ~ :thumbup
 

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Discussion Starter #7
Ok so I have an update guys:

Went to Orielly auto parts, the guy had a code reader he plugged into my bronco. I got 3 codes:

DTC 539- A/C or Defroster ON during KOEO test
DTC 452 - Computer detected an error in the VSS or PSOM signal during the last 80 warm-up cycles.

DTC - 173 - HEGO sensor circuit indicates system rich (right side)

I think the 3rd one is the only one that pertains to the issue I am having. So I am guessing this is telling me I need to replace the oxygen sensor right? Any advice on this? any help would be much appreciated.

Thanks!
 

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sounds like it is an oxygen sensor especially since the code says its reading rich. plus that is most likely an original o2 sensor and would need replacing
 

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the O2 probably needs replacing, heck replace them all as they do wear out.

How ever I do not think thats your problem. it is most likely a fuel delivery issue, or the TPS as said before.
 

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yes i agree with jopes i just replaced the tps on my bronco and seems to run a lot better. Also you may want to consider giving your intake a good cleaning. mine was all dirty and gunked up. definitely made it run smoother for sure.
 

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Discussion Starter #11
the O2 probably needs replacing, heck replace them all as they do wear out.

How ever I do not think thats your problem. it is most likely a fuel delivery issue, or the TPS as said before.
Ok thanks guys. I think I will try the TPS first. Everyone seems to tell me thats more likely the problem rather than the oxygen sensor. I will try replacing the TPS tomorrow morning. If it doesn't fix the problem I can always return it. I was also told I can just take the oxygen sensor off and clean it then put it back on. Is this true? And is there a way I can test the TPS to see if its bad and needs replacing or should I just go swap it out?

Thanks
 

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You should check the tps before just replacing it
 

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If you do need to replace the O2 sensor consider the Denso O2, it's supposed to be a better product then Bosch which has a tendancy to run rich, there's technical explanation why around here somewhere.

The TPS back probing test procedure is in the Haynes Repair Manual where you stick pins thru the 2 wire leads, key on engine off and using a multimeter test for correct voltage setting but check to be sure.

^

Refer back to post #5



Good Luck ~ :thumbup
 
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