mach is jerking while driving.
 

okay, trying to figure this out, maybe someone can post a thread of this. but the mach I just got is having some issues already that it did not do while test driving. Just a little back story, it has Dss Racing 5.0 and cams, other add ons and been dyno tuned.
The guy selling it said that he really hadn't driven it for a year and half and would go from time to time to start it up and let it run, do not know how often. Before I bought the car, I asked him to do a oil change and compression test. I have the paperwork to show that he did both those things the morning I went.
I went and test drove the car and it acted fine.
My road trip home was over 3 hours and about an hour into the trip, I had to take the exit, when I pushed in the clutch the car dropped rpms and died on me. I had to start it right back up. I had this problem in my other mach and we either retuned it or i changed the IAC.
The next thing that it is wanting to do and did not do this while test driving is jerk really bad while barely pushing down the throttle to hold speed. jerking meaning it is cutting out, skipping that drip of fuel to keep it steadly going.

Has anyone dealt with this? again the car basically was sitting for over a year and the guy said that it had no issues like this when he got everything done to it and then when he took it that morning to get the oil change. Also when I test drove it nothing.

Here is my plan, before i'm going to throw it back on the dyno and get retune, I want to try somethings out. like if something got dirty from sitting.
I did put some fuel line/injector cleaner in, but haven't ran it long enough for it to go all through the system.
-put new IAC on. (311-420 is sending me one Thank you)
-check the TPS to see if it needs replaced or adj.
-change the in line fuel filter
-new spark plugs
-check coil pack

Anything else yall can think of.

just side note, when going through the gears to get up to speed it acts fine, at wot it feels solid, it is just when holding a speed it starts to do it.

ASh

Re: mach is jerking while driving.
 

one more thing, when in neutral and barley pushing in the throttle it does not do anything, it is only while driving. I tested it out to see if it would do it while parked, but did not mess up.

ASh

Re: mach is jerking while driving.
 

Had similar problems, got a re-tune and problems went away. Might also be water in the fuel or coil pack issue as you mentioned. I tend to think a tuning issue, though.

Re: mach is jerking while driving.
 

That is my worry, but after talking with the seller, we both started thinking.
The issue didn't start till after the compression test, which made us both think that maybe a spark plug may not be tighten all the way down.
I'll be checking in the morning, it be worth looking into.

ASh

Re: mach is jerking while driving.
 

Yeah....sounds like a misfire. Coil probably. Make sure they're all plugged in well.

Re: mach is jerking while driving.
 

Can you describe it like snakebiting? Where you foot the throttle to go and occasionally that first initial go has a delay or jolts or a combo of both? I had this and it turned out two of my COP connector plugs had poor connections. I ended up soldering on new connectors to the harness. I never had a CEL come up when I had this problem. You might check the COP harness connections when you inspect the COP's.

Re: mach is jerking while driving.
 

no that isn't what it is doing,

ASh

Re: mach is jerking while driving.
 

already checked them to make sure spark plugs were tighten down, then pulled out to see how the condition was, they looked good.
check the gap, all of them the same.
tighten back in and made sure the coils were pushed all the way in.

ASh

Re: mach is jerking while driving.
 

UPDATE:
Well after driving the mach a little more and getting the full tank that I added the fuel system cleaner, at almost half a tank, I was on the interstate, the car suddenly changed behavior, before that it was jerking really bad, but suddenly cleared up.
I ended up before this, returning the mach to stock tune and then re upload the performance tune. This time it would not let me see the injectors or maf, but would let me see the gears and idle rpms. So, I switched the gears to 4.10 and put the idle up to over 1000rpms.
after it changed behavior, I was on a back road where I could come to stop and lower speeds and it was not acting like it was with the jerking.
I drove it a little while ago today to see if maybe I got lucky and it did fine. It only jerked in one of the gears but didn't the rest of the time.
I also changed the IAC, when I took the other one off it didn't have a gasket, but thanks to 311-420, the one he sent me had the gasket with it and put that on with it.
I still think this Mach needs a retune on the dyno, but I want to believe that it was from the car sitting for so long, even though he started it up; I have a theory.
My theory is: that while the car was sitting and even though it hadn't been driven for over a year and half, there was junk building up in the fuel line.
I believe this junk doesn't have time to build up if we are driving the car more often, but when sitting it just built up.
After I started drying it that junk was getting in the way while at lower rpms and causing the jerking problem. Now while it was fine going through the gears and wot, is because there was so much pressure that the junk build up wasn't effecting it, only at idle and holding speeds.
I think the fuel system cleaner helped out to clean that out.

Again this is my theory, do not know if I am correct, going off my own personal time with the car and what the owner has told me.
I have kept him updated and he has also check on the car. He also feels bad and said that if I go get it redyno and tune he would split the cost with me. To me that isn't a seller that knew there was a problem with the car. I think it was just timing on everything.

ASh

Re: mach is jerking while driving.
 

Update:
Well after some time now with everything, for the most part the Mach is driving normal. I truly believe the IAC helped the idle/rpm's dropping problem.
I believe the fuel system cleaner helped too and plan to do some more of it down the road.
I believe the car truly needs to be dyno tuned again to correct any problems.
Just happy it is driving normal, instead of jerking like crazy.

ASh

Re: mach is jerking while driving.
 

Glad it's running better for you now!

Re: mach is jerking while driving.
 

It is running much better.

ASh

Re: mach is jerking while driving.
 

While the Mach is running much better, it still sometimes has a jerk or two while driving it at the crusing speeds. I went ahead and bought a new motorcraft fuel filter, maybe the one on there has never been changed out, i'm not for sure, but if it hasn't, i'm sure it maybe causing some of the problems that i'm going through.
Now the fun part, of getting under there and swapping it out.

ASh

Re: mach is jerking while driving.
 

fuel filter is installed and I believe it made a big difference.
Didn't feel any jerking at all with the few miles I took it for a text drive.

ASh

Re: mach is jerking while driving.
 

Good deal. This car is getting sorted!

Re: mach is jerking while driving.
 

Honestly it is, all the little things getting worked out.
I'm sure it didn't hurt swapping it out with a new one.

ASh

Re: mach is jerking while driving.
 

So after putting a few hundred miles on it after the fuel filter got installed, I believe that was the problem. I believe the fuel system cleaner cleaned some fo the filter up, but did not get all of it.
It drives really well now compare to what it was doing.

311-420, thanks so much for the IAC, I think it not having the gasket on it made a big difference, it hasn't died once after it got put on

ASh

Re: mach is jerking while driving.
 

Glad you got it sorted. I had issues with mine stalling out after going highway speeds, and putting in neutral while exiting the interstate on an exit ramp.

It also idled very rough, and would sometimes stall out sitting at a stop light.

Troubleshot it down to a bad 02 sensor, posting here in case any one else stumbles on this thread and doesnt have success with what fixed yours.

Re: mach is jerking while driving.
 

Thanks, I guess I should have said that, mine has them shut off on the tune and MIL's also.
But that is good point for anyone in the future, which I'm sure there will be. :mrt:

ASh