My truck 96 Ranger 4 cyl 2.3 5 speed reg. cab as a hesitation/miss at light throttle only, no misses at idle. I installed a new pump about a month ago. I thought it was just relearning. I decided to check the fuel pressures.

Are these values acceptable?

PSI Hanes Manual Results

KOEO 32 35-45 low

Idle 30 25 ok

1500 RPM 28 none ?

Regulator disconnected 39 35-45 ok

Off AFTER 1 MIN. 25 drop 5 ok

AFTER 5 MIN. 18 drop 1 ?

AFTER 6 MIN 16 drop 1 ?

AFTER 10 MIN 12 drop 18 ?

AFTER 15 MIN 10 drop 20 ?
Thanks
Johnny

 

I don't think fuel pressure is your problem.

If you have access to a scantool, have a look at the TPS, MAF & O2 sensors PID & the fuel trim numbers & post the results.

If you don't have a scantool, I suppose you could do a TPS resistance profile with a good quality analog multieter, to see if you have a dead, or flat spots in it's travel just off the idle position.

The scantool could provide some insight into how the MAF sensor is responding to increased air flow, when the throttle plate opens, in case it's dirty & slow to respond & how fast the O2 sensors are switching & what happens with fuel trim, in case they're old & lazy.

It'll also show how the TPS responds to throttle movement.

Some thoughts for pondering.

 

pawpaw thanks for your reply.
I did hook up my scantool but no new codes. Is there away to view the other data without having a DTC thrown, it's a Harbor Freight Cen-tech model. I do have the data saved from the last time I had a code about a month ago, that information is on my last post along with what else I did plus new motorcraft wires.
I do not have an analog meter, I used my dvom and back probed the wires koeo closed 0.86 open 4.66 volts. Unpluged TPS ohms closed 3.56 open .34 did not seem to have any flat spots.
I hope this is understandable.
Thanks
Johnny

 

We don't know which instrument you have, but a Scantool can read the computers various sensors PID's, so if you have a real scantool, just hook it up to the DLC & follow the instruments instruction manual for scrolling through it's menu & retrieving the various sensors PID readings & post the numbers.

If you don't have a scantool, just a code reader that'll only retrieve & erase codes, then you'll have to use your multimeter to backprobe the various sensors electrical connectors to read their PID & that can be a real pia!!!!

 

PawPaw thanks again,
I guess my scanner just dosn't read any data unless their is a DTC.
I forgot to say I also checked the vacuum it was good held steady at 23#.
I also checked my IAT Sensor which didn't check out, temp. 86 resistance .01.
I just unplugged it and it runs good! what do think can I assume a new IAC will fix this, wiring seems ok.
Thanks again
Johnny

 

I did a search on what are the symptoms of a bad iat sensor an this came up.

IAT - Intake Air Temperature Sensor

Symptom dosn't cover my problem but the truck runs fine when it's disconnected.

Thanks
Johnny

 

Ok good testing & feedback.

Looks like the vacuum is ok, which suggests valve & piston ring sealing is good..

Well, to get back to your initial post about a slight hesitation problem.

Most of these hesitation problems sorta center around things like a problem with the TPS having an open, or flat spot in it's resistance reading & sometimes thats difficult to see on a DVM & is the reason I suggested using an analog type meter to test it.

You'd want to open the throttle very slowly, or as you do when you feel the hesitation, so you could spot any brief drop in it's resistance reading as the throttle is opened. Going too fast could cause the the meter to miss the anomaly.

Another suspect for your list is the MAF sensor. If it's dirty, that could cause it's response to be slow in sensing a change in intake air flow into the engine as the throttle plate opens & that could upset fuel trim.

Lazy O2 sensor switching speed also belongs on the suspect list as I posted earlier.

I suppose dirty fuel injectors, or a clogged fuel filter may be suspects also, but your not complaining of other driveability problems, so at this point they probably haven't earned a spot very high up on your susprct list.

You might go to http://www.fordfuelinjecton.com & look up the IAT sensors resistance profile vs temp chart & see how yours tests out.

If your using an oiled foam, or cotton gauze air filter, or have a dirty or damaged air filter, filter seal, or air box, or the air box isn't buttoned up properly, the MAF sensor could be dirty & in need of cleaning.

If so, use CRC MAF sensor spray cleaner as specified, on a cold/room temp sensor, don't touch the sensor with the probe & keep it squeeky clean upon installation.

 

PawPaw thanks again,
If it's the TPS would it clear up when I disconnect the IAT?

This link http://www.tomco-inc.com/Tech_Tips/ttt8.pdf indicates it will cause a hesitation problem, what do you think?

The forward O2 sensor was replaced about 2 yrs. ago.

I pulled the connecter from MAF today and it stalled, I cleaned it about a month ago CRC MAF sensor spray cleaner.

No check engine lights are on.

It's really running good with the IAT disconnected.

Thanks again
Johnny

 

Well if the IAT sensors resistance value doesn't check out with this chart & the problem clears up when it's disconnected, then I'd consider replacing it.
Ford Fuel Injection Air Charge Temperature (ACT)

 

I THINK that a bad IAT can cause various issues because the pcm uses it to help figure out how much air the engine is getting ( in a MAP system IIRC).

Anyway, when you disconnect it, the pcm probably uses a nominal value that works OK under 'normal' conditions. It may have been off just enough to give you issues, but not enough to cause fault codes.

That's my theory anyway. Hope it works out for you.

 

First I want to think you pawpaw, for all your help and advice.

I went to pickup the IAT Sensor and I had a DTC P0113 because I disconnectd the sensor. My scanner would read and erase the code but still wouldn't read the freeze frame data.

I guess I'll try it on another vehicle and see if it's the scanner or my truck.

I drove it about 20 miles today it seems fine.

ford2go
Thanks for your reply.

It did seem to fix it, if anything changes I'll give a post.

 

OK, good find, fix & feedabck on your hesitation problem fix.

The IAT isn't often associated with a hesitation problem, so it's often overlooked in a trouble shoot.

SO, this is good info for everyone to put in their hesitation trouble shooting scenario.

 

Just out of curiosity I was looking around and found this link with a lot of information on IAT'S.

Engine Air Temperature Sensors

Thanks again, I do enjoy this forum.
Johnny

 

Nice link on the IAT tutorial.
Larry puts up good useful info on his site, I've refrred to it often over the years.

 

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Wow. There is a ton of really good info on that AA1Car site. Thanks for the link.
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