# Hesitation during acceleration. Suggestions needed



## mike in SC (Apr 29, 2004)

Hi. Having what I hope to a common issue with my 88 Fox. It uses CIS-e. Hesitation during acceleration and after gear changes. At WOT no hesitation. Problem presents itself as either on/off.

In the last week I have replaced/checked the following:

Fuel filter
With the wire harness disconnected from the DPR the car goes into limp-home-mode
ALL vacuum lines in engine bay
Checked intake boot for cracks:none were found.

Hot or cold the engine starts perfect every time.

However, the engine stumbles and generally hesitates under gear changes and acceleration. Hesitation is generally felt more under 4th gear acceleration ( It's a 4 speed manual). Living in SC, in an area that is hilly, so it's an issue. This Fox is not a primary car, but it is one I use for yearly auto-x events. Hesitation is something working against the clock.

The hesitation stops when in WOT. It runs as it should, without hesitation. 

While I am not entirely convinced that the issue is isolated to only the fuel system, I am not ruling out this possibility. I am going to replace the cap, rotor, wires, and plugs after further review.
So.......
1-Would the o2 sensor have much to do with the issue? Because the car goes into limp mode when the harness is disconnected, it would seem that the oxygen sensor is working properly, but I cannot be sure. 
2- CTS sensor. I'll be check the ohm resistance later this week.

All tests to be completed per bentley procedure.

Is there anything else I might have missed? Suggestions? 

Thanks


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## cuppie (May 4, 2005)

How it runs with the DPR disconnected doens't reflect one bit on how well the O2 sensor is working. 
For that, try running it with the O2 sensor's signal wire disconnected.  

How's it run during warmup? If it's fine at startup, and during initial warmup, but goes to crap at about the point the engine is up to normal temp... that points to a failed O2 sensor.
Also, the fact that it runs fine at WOT points here, too - the O2 sensor signal is disregarded at WOT.

But, your initial thoughts (coolant temp sensor, and/or O2 sensor) are the two most-likely things that would cause this. Both are cheap, too - a new CTS is ~$15; a new O2 sensor can be had (so long as you don't mind splicing wiring) for ~$40 (Bosch 13942 or 13953 - 'fits' '90-ish Mustang 5.0; just cut & splice your O2 wiring to it.)


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## cabby85 (Feb 28, 2009)

my 1985 cabriolet has the exact same problem, however it seem to have a mind of its own when it want to run fine and when it runs like ****. Also when it's shuddering I can hear the CIS plate "popping" kinda sounds like its slamming up or down I was checking for vacuum leaks and found one hose that when pinched the car idles smoother and it revs fine. Once the car warms up it seems to run a little better. I have already replaced to o2 sensor which made no difference. I really need to diagnose whats causing this since its my daliy driver


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## mike in SC (Apr 29, 2004)

I drove the wagon with the o2 sensor unplugged. Drive better w/o hesitation. Replacing it soon.


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