Hesitation on light throttle


PeteK

GT Owner
Apr 18, 2014
1,759
Kalama, Free part of WA State
In the last couple weeks I've had a minor problem come up. I am getting a light hesitation/surging when I go from coasting to light throttle, and sometimes when I'm cruising along at light throttle. It feels like an intermittent lean condition. It runs perfectly under higher throttle and idles smoothly. No CEL. I don't have a code reader yet (it's on my list).

I did a cursory look around the engine compartment to see if any hoses were loose or cracked but didn't see anything obvious (I particularly checked the hose one of you found a few weeks ago that was deteriorated). I have not yet done a propane test or anything like that.

I have enough to do with getting ready for the rally and the eclipse and being out of town for two weeks, so I don't want to add more to my plate, and I'm looking for a shortcut (yes, I know, that invites Murphy to get involved). Anyone had a similar experience and quick solution? Injectors dirty? Spark plugs? Anything else?

Speaking of spark plugs, what's the latest recommendation on those?

When I search the Tech Forum for "hesitation," surprisingly, there's not much in past threads about this.

TIA
 

nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
4,006
I'd be doubtful that it was either sparkplugs or dirty injectors. Not sure what mods you have, if any. Stock throttle body?

My instincts would be with 1) Malfunctioning MAF sensor (suggest removing and spraying with MAF aerosol cleaner - auto parts store) and/or 2) bad/old gas
 

PeteK

GT Owner
Apr 18, 2014
1,759
Kalama, Free part of WA State
Thanks for the reply. Not old gas (I fill it up every 1-3 weeks). No mods, stock throttle body. I'll try cleaning the MAF sensor. later today or tomorrow

Thanks
 

Art138

GT Owner
Mark II Lifetime
Jan 4, 2011
541
Weston,FL
I have the Torrie tune and was advised to use TR6IX NGKs with a very tight gap.
 

PeteK

GT Owner
Apr 18, 2014
1,759
Kalama, Free part of WA State
Art, thanks. I'll but a set of those, because the current spark plugs are probably around 25Kmi.
 

FlagstaffGT

GT Owner
Mark II Lifetime
Look into part 4G7Z9E498AA connector , less than $75, rear most vacuum line connector on passenger side rear of supercharger. Sort of an octopus vacuum line assembly. Mine was loose and sucking air after 65k miles. Some similar symptoms and a O2 code when it gets bad enuf. Plugs should be good to 100k, just had mine replaced.
https://www.concord-parts.com/images/items/ford/4/4g7z9e498aa_ford_2.JPG
 

PeteK

GT Owner
Apr 18, 2014
1,759
Kalama, Free part of WA State
Thanks for the suggestion and part picture. It sure is an octopus. I'll check it tomorrow. I know plugs are supposedly "100Kmi" items now, but that seems a bit long to me. I will at least pull and inspect them, and put antisieze on the threads--learned that the hard way when I drove VW air-cooled engines several decades ago.
 

TO AWSUM

Ford GT Owner
Mark II Lifetime
Jul 4, 2007
1,435
Niceville FL
Agree with all the above. Hesitation is usually a fuel issue. Not getting the correct fuel air mixture at the proper time due to vacuum leak, MAF, etc. Missing is usually an electrical problem like plugs, wires, or points on an old 1960s distributored engine. I also doubt it's spark plugs. Use the OEM plugs or the plugs recommended by the person who modified your engine. Getting a plug recommendation from someone that doesn't know your engine mods is looking for problems.

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soroush

Ford Gt Owner
Mark II Lifetime
Aug 8, 2007
5,250
if the MAF was failing wouldn't there be a code? if there is a miss isn't that a hesitation? :) I would take out the plugs and at the very least clean the contacts and just stick them back in to see if it makes a difference. easiest thing to check first without having to buy anything and if this doesn't solve the issue at least your one step closer
 

TO AWSUM

Ford GT Owner
Mark II Lifetime
Jul 4, 2007
1,435
Niceville FL
Soroush, a hesitation is a sluggish response during initial acceleration from a dead start or rolling start. Engine still runs smoothly, just unresponsive or slow to start it's performance. Missing is like an engine cylinder shutting off momentarily and usually occurs during higher acceleration demands of the engine.

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nota4re

GT Owner
Mark IV Lifetime
Le Mans 2010 Supporter
Feb 15, 2006
4,006
if the MAF was failing wouldn't there be a code? if there is a miss isn't that a hesitation? :) I would take out the plugs and at the very least clean the contacts and just stick them back in to see if it makes a difference. easiest thing to check first without having to buy anything and if this doesn't solve the issue at least your one step closer

No, there is typically not a code with a failing MAF if the values are inaccurate but still in range. I wouldn't have suggested that as a culprit if bad MAFs always threw codes.

It is VERY unlikely that it is a spark plug based on a lot of experience - that's why I didn't go there. If it was modified and making a LOT of boost and had hesitation at the high-end, THEN I would look at spark plugs.

I would look/clean the MAF sensor and I think the other input here regarding the spider web of vacuum lines under the throttle body is another good suggestion.
 

PeteK

GT Owner
Apr 18, 2014
1,759
Kalama, Free part of WA State
What's a new MAF cost? It might be easier to just replace it, see if that clears up the hesitation, and have a spare.
 

jbyrnes

FORD GT OWNER
Mark II Lifetime
Jun 13, 2006
224
Louisville CO
Unlikely since you're not seeing the problem at idle or under load, but I had a similar sounding issue in a different car a few years ago, and fixed the problem with some dry gas. The gas in the tank was fresh but I filled just after flooding rains so I assume water got into the tank at the station. I recall it was most noticeable in midrange throttle.
 

Nafod

GT Owner
Mark IV Lifetime
Cleaning the MAF is fairly straight forward. Did it to my F-350 and was amazed at how dirty it was while looking fairly clean. Don't want to touch any part of the metal sensor, just let the spray do the work. I would think as Kendall said, it's probably not a bad MAF because you have no codes. Just may be dirty.

We use to spray non flammable carb cleaner around vacuum lines to see if the engine would stumble at idle to confirm a leak. I assume this would still work for the GT, but havent done ANY troubleshooting around a forced induction engine. I'm sure someone can till you if its a good check.

As for water in the fuel, didnt you guys just have 8 inches of rain in a day last week?

Or, it may be the beginning of the fuel filler valve problem if you haven't had that yet, , which again is another vacuum leak.

Just throwing things out there, I'm sure this is frustrating.

GL with the fix, See you at the Rally,

Bruce
 

paul b

GT Owner
Nov 2, 2006
810
Take a look at the air filters, you never know.