Hesitating, problems accelerating

[FordFestiva]

My problem is different and only when engine is cold (just after starting). No coughing. Just a subtle hesitation which I never experienced in the past when starting off in either first or second gear. And only when cold. Once engine warms up, it drives fine. I also may remove and clean the engine coolant temperature sensor. Maybe that's not operating right and not sending enough gas when it's a cold condition. I am also going to test the resistance of each spark plug wire and clean the distributor cap and rotor.

This is my 100th Post!!! This is a great forum and appreciate every ones help! THANK YOU !!!!

[kjchernov]

Oh, sorry, I must be misunderstanded your 1st post

[FestYboy]

My problem is different and only when engine is cold (just after starting). No coughing. Just a subtle hesitation which I never experienced in the past when starting off in either first or second gear. And only when cold. Once engine warms up, it drives fine. I also may remove and clean the engine coolant temperature sensor. Maybe that's not operating right and not sending enough gas when it's a cold condition. I am also going to test the resistance of each spark plug wire and clean the distributor cap and rotor.

This is my 100th Post!!! This is a great forum and appreciate every ones help! THANK YOU !!!!

ok that makes a differance, being only a cold start issue. wish you would have stated that earlier ( if you did, i missed it).

[JohnGunn]

My problem is different and only when engine is cold (just after starting). No coughing. Just a subtle hesitation which I never experienced in the past when starting off in either first or second gear. And only when cold. Once engine warms up, it drives fine. I also may remove and clean the engine coolant temperature sensor. Maybe that's not operating right and not sending enough gas when it's a cold condition. I am also going to test the resistance of each spark plug wire and clean the distributor cap and rotor.

Problems with engine performance, especially when cold, are MOST likely due to marginal spark plugs. Buy a set of NGK V-Power plugs for $10, even if you KNOW yours are OK, and tell us how much better they make you feel.

Good luck.

John Gunn
Coronado, CA

[FordFestiva]

I changed the spark plugs - Champion gaped at .044, air filter, distributor cap, and rotor. I recently changed the engine oil & filter a week before, cleaned the PVC valve in kerosene, inspected and checked all wiring harnesses and hoses. I still experience the hesitation and then surging. Getting worse. I always use Champion spark plugs and should not be an issue. I also checked the resistance of each plug and coil wire, passed my hand along all the wires while engine running - no shock. I removed each plug wire from the spark plug while engine running and can hear the drop in engine idle and the nice snap of the spark arc. If the problem was the coolant sensor or 02 sensor, would the "check engine" light come on. I remember having a problem with the coolant temperature twice and not sure if the "check engine" light appeared. I did replace the 02 sensor July 2, 2005. This hesitation/surge, hesitation/surge, hesitation/surge is happening while engine warm now and becoming worse.

[ejp2fast]

I suggest you to open it's cover, clean MAF (with Vodka or alcohol) .

HAHA thats hilarious... i see you are from Russian so doesn't vodka come out of the tap there?!

[FordFestiva]

My MAF / VAF never got wet. I did tap and no difference in idle.

[JohnGunn]

I had a problem which started with a gentle surging that gradually escalated to a severe bucking which eventually, after exhaustive replacement of various and sundry expensive emissions control parts, turned out to be caused by an expensive set of Bosch 4-electrode spark plugs with less than 3,000 miles on them.

Since then, I believe the best place to start addressing driveability issues is by replacing the most fundamental element of a smooth running engine -- the spark plugs. That remains my best suggestion, but since I could be wrong, I'll assume you did as I suggested, and it did not the fix the problem.

My first problem is that I am not able to witness the symptoms that you describe as hesitation/surge. To me these symptoms point to a failure in two different systems. Hesitation suggests to me that the engine misfires, which is almost always to be traced to a defect in the ignition system.

The term surge suggests to me an unevenness in the running of the engine which does not cause the engine to misfire. The speed of the engine varies but never stops firing. That would suggest a failure of the fuel delivery system.

If I were there I would probably be able to hear whether it is misfiring or not. Maybe it would be easier to hear at the tail pipe. If it is misfiring then the fault is almost surely to be found in the ignition system.

The computer in these cars uses the input of the various emission control sensors to change the amount of fuel injected into the cylinders. It would never cause the ignition to stop working and create a misfire in response to a malfunctioning sensor.

Besides, my experience tells me that most people are too eager to start blaming failing sensors. (I used to be one of them.) I'm more comfortable looking to basic parts which are more likely to fail over time. That said, if there is no misfire detected in the hesitation/surge symptom, I would turn my suspicion on the fuel pump. The most direct way to assess its condition would be to test the pressure the fuel pump is able to sustain. Of course the fuel pressure regulator would have an effect on that, so, in case of failure you would have to make sure the regulator was OK before replacing the pump.

One last thing occurs to me that should be tested before doing anything else. Take a can of starting fluid and go over the whole of the vacuum system with it. If spraying any part causes the engine to surge in speed, there is a leak at that point that must be fixed.

John Gunn
Coronado, CA

[FordFestiva]

We had a '69 Volkswagen van that would not start with brand new NGK plugs. We put the old Champions back in and it started right up.

[FordFestiva]

I usually use propane torch and follow the vacuum lines with it.

[FordFestiva]

The surge, pause, surge, pause, surge (jerk) is only starting off in first or second gear - otherwise idle and cruise is normal. I do seem to have a subtle loss of overall performance (acceleration). I recently installed 13" aluminum rims and new tires, do you think this is the problem?! ;-)

[FordFestiva]

Maybe I should not use the term surge. It's more of normal acceleration but consistent pausing during start off in 1st or 2nd which causes the jerking.

[Crankworm]

I'm just trying to follow this tread and was wondering if the terms vaf and maf are being interchanged here? Is everyone referring to the airflow meter thingy on top of the air box?

[JohnGunn]

The surge, pause, surge, pause, surge (jerk) is only starting off in first or second gear - otherwise idle and cruise is normal. I do seem to have a subtle loss of overall performance (acceleration). I recently installed 13" aluminum rims and new tires, do you think this is the problem?! ;-)

If you had a carbureted engine I would say this sounds like a failing accelerator pump. So what does the fuel injected engine do to replace the accelerator pump?

My 1990 service manual describes several engine operational modes and the action of the system during them. One of the modes is the Acceleration Mode. Included in the description of this mode is the following statement:

"This mode is activated when the PSW switch in the throttle position sensor is closed or when intake manifold vacuum is below the specified vacuum. Because a vacuum sensor is not used, the ECA calculates low intake manifold vacuum using the input signals from the crankshaft position sensor and vane air flow meter."

The PSW switch in the throttle position sensor is activated when the throttle is opened at or beyond the 70% position. So, unless you're driving like a racer, this should not be causing your problem. Still it is easy to test to see if the two switches in the TPS are working at the proper positions.

The VAF meter has a vane inside it that moves as the volume of air passing through it increases. That is a physical movement which could eventually become restricted in its movement and, therefore, slow to react. Easiest test would be to swap in one know to be in good condition. Short of that, it might be possible to carefully take it apart and check for free movement of the vane.

Of course, all of this would be wasted if the problem is a failing spark plug.

Good luck. Let us know how it turns out for you.

John Gunn
Coronado, CA

[FordFestiva]

I believe I just solved my problem. I was checking all the wiring harness connectors, probed around with a propane torch checking for vacuum leaks and found that the wiring connector for the engine coolant temperature sensor was not snapping and secured in place. The securing portion of the connector is broken or something missing. I used a plastic tie to secure it in place and runs like a champ once again. I'll put it through a few day test and follow up.