3.2 carrera bucking

[r_towle]

I have read quite a few of the threads pertaining to bucking.

Is there a way to test the speed sensor and TDC sensor?

My problem seems to come and go, mainly appears under load.

Not sure where to start testing, but it may not be the sensors, it may be the fuel pressure regulator.

Again, this is not a contant issue.
New fuel pump relay, BTDT.


Rich

[stlrj]

Why not consider an ignition tune up and go from there?

[BE911SC]

My '84 'bucked' a little at times so we changed the intake gaskets and spacers. Found a cracked vacuum line and heat-shrinked it and the car now runs smooth. Night and day difference.

[r_towle]

bucking...hmm
It coughs sputters and in some cases shuts off.
Almost like the car is shutting off and on and off and on.
If I catch it, I push the cluth in, rev it up and resume going forward...
Then it may do it again, or not.
Sometimes it dies all together.
I am rolling, so I dump the clutch and jump start it, off we go.

If I keep my foot on the gas, it feels like bucking but I believe its shutting off and on

It is starting to happen more often.

Rich

[ChrisBennet]

Come on over some time and we'll scope out the sensors. Give me a days notice so I can put the scope on the charger the night before.

[r_towle]

Long time Chris....
I am wondering if its the DME soldering issue.
Seems the ignition circuit ground transistor is one of the frequent loose connections.

I wiggled the ignition key and I could not reproduce the issue.
Sure seems like a full power drop, then on...

Should be loads of fun to track down.

Rich

[twistoffat]

When did you last change the fuel pump Rich. Last time I had bucking it was dirty fuel.

[rgdtoo]

Bucking huh.. I just posted the same issue then noticed this thread.

I too was thinking maybe dirty gas messed up the fuel pump or a vacuum hose or something.

ANYWAY, Thanks for some places to start.

BOB

[scarceller]

Here goes:

1 - Check for vacuum leaks
2 - test ref/speed sensor resistance needs to be 1000 ohms +/- 10%
3 - test the AFM by measuring it's output voltage while you swing the barn door from fully closed to fully open. Test the 1-3vdc area very slowly and carefully as it spends most of the time in this area.
4 - test CHT sensor resistance, at room temp 68F it should read about 2800 ohms
5 - DME solder joint, if you suspect this send me a PM, I fixed as lot of these. Also Chris Bennet and I know each other I'd be happy to help also.

Also fill the tank with Gas and see if this helps, I had the screen filter in a tank so gummed up that it restricted fuel and once the tank got below 1/4 full it had issues.

[r_towle]

New fuel pump and filter last year.
I made it almost to hershey before it did it, and then it acted up for a minute or so at about 80mph...then stopped for the weekend.

Its getting more frequent now.

I did all the vacuum leaks, intake tightening, hose replacement, icv testing etc last year.
I will go check all that again first, but the oil cap off still lowers the idle just right.

Had the valves done last year by a professional, and oil changed.

So, while it may be fuel, it sure seems electrical.
Wierd part is if I push in the clutch and floor the gas pedal, or pump it, it comes back to life...then I drive on...and it bucks again.

I cant figure out which way to look...fuel or electrical.

I suppose fuel is easy enough to rule out first...

Oh, it also seems to happen under load...so accelerating, but not flooring it, just pushing it up ten mph on the highway to pass a car....bucking...

Downshift, no problem.
Push from 60 to 75 in 5th and it bucks.

Hey Chris
I have a nice four post lift now...maybe you would come over and figure this out with me and we can talk about using my lift when you need it

Ahh, one more thing that I forgot that may provide a clue.
I hit a car last year...just finished replacing the passenger fender, bumper, foglights, and one headlight.
All seem to work now.

Maybe I doinked a simple relay loose....hmmm
or a fuse...

Rich

[twistoffat]

Rich, how low was your Tank when you made it to Hershey.
pushing from 60-75 and bucking were exactly the symptoms I had with dirty fuel. When I downshifted and accelerated in 2 or 3 quickly it disappeared. On the Freeway at 60 in 5th accelerating slightly it started to buck. It did this a few times. I drained my tank completely put in new fuel and a squirt or injector cleaner and the problem went away. If the fuel was dirty and you ran the tank low going to Hershey I suspect dirt clogged the system somewhere. That doesn´t mean it is the problem but having experienced just that it seem like it. Have you also tried swapping out the fuel relais

[scarceller]

If you can get hold of another DME I'd try replacing the DME to see if issue goes away.

[ivangene]

Ive been chasing this one too and will give you a list of things I did that made changes:

valve adjustment - I mean really nailing it...Ive done 3 so far and this last one I got them "perfect" - there is a "feel" and I am happy to report this had an effect on the bucking

AFM adjustment using a CO% meter - We had a bad meter and i was running way richer than I thought

Idle switch - make sure it is "clicking" at the right throttle position

and this one - the wiper on the AFM arm - I have yet to do it....but finding a new track for it to wipe on - there is a test and repair here:
http://www.the944.com/afm.htm

[scarceller]

The AFM carbon track can easily be tested, just turn key to run (but don't start the car) then measure voltage on the green/red wire, this is the 0-5vdc output for the AFM. While you keep an eye on the meter slowly push the barn door open with eraser side of a pencil. You should see a clean sweep 0-5vdc as the door is opened. Pay close attention to the 2-3vdc range.

This picture will help:

[EMJ]

Ignition coil or spark plug misfiring? Have these been checked? I might've missed it. If the joints on the DME have been soldered and are cracked again, the car would simply shut off when a bump is hit as the connection is lost and the car loses power.

[r_towle]

so, this seems to be something electrical.
Driving along yesterday...now its happening more frequently.
Just driving along....car goes on, off, on off...I push the clutch in to keep from bucking...car dies eventually.

I roll of the road, turn the key off, then start the car...still rolling, with no rest.
Started right up, drove another hour with no issue.

Starting to think it might be the ignition switch.
I was wiggling it when it died to see if I could get it back on again...just to see if I could make it do something odd...like run or die.

It may have felt like it, but I am not sure.

So, to replace the ignition switch electrical portion I read the article from our host.
How do yo remove those break off bolts?
They dont look like they will turn and it sure looks like any dremel attachment could hit the dashboard...

There must be a special tool out there for this...

rich

[scarceller]

I used small vise grips to get those loose.

[pete3799]

I used a good sharp prick punch and put a dimple out near the edge of the bolt then angled the punch and tapped it around. After they were out i ground a slot in them and reused them.

[JQ911]

Mine bucks or jerks on 1st gear while crawling in slow traffic between 1 to 3 mph underload not stepping on the gas. its like riding a mechanical bull.

[1989G50]

Doubt this will help anyone? Mostly depressing. I've had the dreaded hesitation disease for 3 years now on my 89'. I started with the fuel pump, no luck. Next was the ignition switch. Yes, those screw are tricky. I used mini socket set with Phillips bit and it still 1/2 hour per screw. That didn't work either although made the "buck" less dramatic. DME relay, wasn't that. Checked inside the brain for cracked solder. I couldn't find any. The last thing I did was change the ignition coil. Was not a fix although I can positively say that hesitation. Was not as frequent or violent. A while ago I read something here about a fuel cut-off relay related to the alarm system(or not) being triggered because of excessive heat or vibration? It might make sense in terms of how of the sudden the "buck" can be. Anyway, like someone else said there's a lot of good reading on the subject with tales of all injectors being replaced and more! I would lean torwards electrical but some guys have said adjusting the mixture did it.