My car has developed an extremely annoying bucking under acceleration. It started about a week ago, and at first it would only happen while accelerating out of a fast turn. But now it does it all the time while accelerating. It's like the car is oscillating between half power and full power, making it lurch-slow-lurch-slow-lurch-slow. It's like you're riding a bucking bronco or something. The only cure seems to be to get off the throttle completely, upshift, then slowly accelerate.

Anyone have any idea where I should start looking first?

sounds like a lack of fuel.

When you get the bucking worked out check your motor mounts and make sure you haven't broken one or both.....

Don 't know if the TPS would cause bucking to that extreme, but it would be worth looking for tracks.

Car still have the Djet?

Has the tank ever been cleaned along with the bottom screen replaced?

John

Motor mounts and trans mounts are still good.

TPS has been on my to do list. I should check it anyway. The stumble isn't while cruising though, which I understand is what happens with the TPS. My problem's only with acceleration.

Yup, still D jet - it's in the sig!
It's anyone's guess if the tank has been cleaned or the screen replaced. I've only owned the car since last november, and I wouldn't trust a word the PO says about it.
That seems logical though, considering the issue started with hard cornering. Maybe some sludge got knocked loose.

Any chance a dying fuel pump would cause this?

Just curious before I start pulling the tank out.

Yes, or bad regulator, or clogged line, or something else...

Check all of the vaccum lines. there is one in particular I have experienced that is buried under all of the F.I. It is a large 3 way that ( IIRC) connects the Decel valve, Aux air reg and the intake manifold together. That will cause symptoms like you are describing. there are diagrams somewhere on the site.

When my 2.0 did this, it was the trigger points in the dizzy. The contacts were good but the dogs that rides the cam on the dizzy shaft that open and close the points was worn out so they weren't opening fully.

The TPS provides accel enrichment. You can spot check by turning ign on w/o starting engine, then go to engine and operate throttle valve. You should hear clicks from the injectors firing.

Mine did this. Did a LOT of things to try to fix but I think it was overhauling the dizzy that finally did the trick. Also check all grounds.

Could be a loose ground wire on your distributor plates. Simple to check, just pop the dizzy cap, remove the rotor and dust cap and look at the ground wire connecting the plates.

I've replaced all of my vacuum hoses and recently repaired my AAR. I know the 3 way you're talking about. I'll check it to make sure maybe something hasn't come loose there while I was replacing the AAR.







All you guys talking about the dizzy have me thinking. When I got the car, the vacuum canister was missing a screw and was hanging out of the dizzy causing the car to run waaaay underpowered. When I reattached it, the power came back. It does feel like the car is flipping back and forth between the feel of those two instances. I'll check this out.

Is there a good guide to overhauling the dizzy, plates, trigger points, etc?

What's your fuel pressure?

I'm surprised that no one has mentioned the fuel filter.

I think it's probably worth reading this thread: D-Jet Troubleshooting. It's what I used when I serviced my dizzy. The whole thread is worth reading, but it doesn't get to breaking apart the dizzy until midway on page 2.

Good luck.

There's a lot of good advice here. Make sure your vacuum advance is working good. Check that your mechanical advance weights are moving freely and the springs are all good. Timing correctly set? If you clean the trigger points, make sure to only use something like a note card. DO NOT use emory cloth! These things need to shine. You want the resistance as low as possible.

So first I cleaned every contact I could find in both the ignition and FI systems. Didn't help the problem at hand although the engine does run a little smoother.

Then I changed the fuel filter...and holy crap! That was it....mostly. I drove around for about 30 min and the car had completely woken up with smooth acceleration. I did have a couple very slight instances of bucking, and I suspect a professional fuel tank cleaning is in my future. Especially judging by the crap that came out of the old fuel filter! But it's 99% better than what it was before changing the filter.

don't you love the simple fixes

Definitely!

Celebrated too soon

Went for another drive tonight, and it was bucking again. It seems to be way worse when the engine is cold, and once warmed up it seems to go away for the most part.
Arrrgggghhh!

Symptoms indicative of overall lean mixture. Make sure you have at least 30 PSI available at fuel rails. Factory setting was 28 PSI but that was when gas was "real" gas.

Got a friend bringing over his fuel pressure gauge later this week. I've driven through two tanks of gas with the new filter, and the bucking has gone away completely when accelerating in a straight line whether or not the engine is cold or warm, and whether or not I accelerate hard or slowly.

The bucking has also gone away under hard cornering only if I complete the downshift prior to starting the turn and maintain 3K+ revs through the turn. But if I shift during or after cornering hard, the bucking happens while trying to accelerate away from the turn. I can power through the bucking by putting the pedal to the floor, however that's not always possible with traffic.

I'll see what my pressure readings are. But for some reason the G forces of cornering while momentarily in neutral are causing the issue.

Disregard that since you have a carb now. You don't have fuel rails anymore. Your carb only wants about 5 PSI.

Check your new filter. If there was a bunch of crap in the bottom of the tank it could have clogged the new filter quickly.

What?
Actually I don't have a carb and I do have fuel rails. Note the car listed in my signature

The car has been performing better since the new filter. Still just trying to work out the last issue under hard cornering.

I would suggest a few things.
A new fuel tank sock on the return line at the fuel tank...
Check all your fuel lines.
Check all your wiring, make sure all the fuel injection wiring is properly connected and not loose...it happens.

Do new points, new plugs, and new wires, rotor and distributor cap.
Remove the advance plates and clean then inside the distributor...40 year old grease is like glue now...

Remove the if trigger points and blow out all the crap from the bottom of the distributor.

Full tune up
Set valves
Set dwell
Set timing
Check fuel pressure.

Now you would have eliminated a large number of variables...it's just a good place to start.

Couple of extra things I thought of:

Check your injectors for flow since your filter was plugged.

Check your MPS....hopefully it is bolted down in the bracket with spark plug wires not near it and not just hanging somewhere. That might explain the cornering issue.

My .02.

Plugs, wires, cap, rotor are all only a few months old. I've put in a new pertronix elec ignition and flame thrower coil also.
FI wiring has been gone through and all contact points cleaned.
Valve adjustment, timing, and dwell has been done in the last couple months.
All FI hoses are only a few months old, and routed correctly.
Injectors are all recently rebuilt - all bought here from a couple different forum members.
All 4 elbow hoses are new. The rest of the fuel hoses are relatively new (I didn't install them, but they're definitely not OE.)

I plan on having the fuel tank cleaned and a new sock installed by a local air-cooled shop here in town.

Is there a good guide somewhere to pulling and cleaning the dizzy? This is really the only other thing I haven't done.

I'll check my injectors again. I did this crap in the wrong order! I went injectors->filter->tank. Doh! At least I know better now, ha!

MPS is bolted down snug. I had to pull it out of the way when I replaced my injectors, and I made sure it was nice and secure when I replaced it.

I say again (from page 1 of this thread), you may want to read this thread in its entirety, including the part about servicing the dizzy. It may help, it may not, but I found it useful for cleaning the dizzy.

In terms of pulling it: most people have to loosen up the timing barrel nut (or whatever you call that 10 mm thing that secures the dizzy in position for timing) and rotate the dizzy counterclockwise. Then you can get a 13 mm socket down there to remove the nut securing the dizzy in place. Once you get that nut out you can pull the dizzy straight out (after disconnecting wires, vacuum lines, etc). Depending on the type/shape of the O-ring seal, it may require some modest amount of force to pull out. Place something like a rag inside the hole so dirt that's hanging out there doesn't fall into the well. I have seen some people say they can get that 13 mm nut off without rotating the dizzy (and messing up the timing), but I was not able to.

When you put it back in after cleaning, notice that the gear is offset so the dizzy will only go back in one way. If you replace the O-ring, keep in mind it might be tighter to get it back in and may require some force.

Also, getting that 13 mm nut back on during reinstall requires dexterous fingers. May want to have your magnet ready to retrieve the nut a couple of times.

I assumed you had already done this.

Get intimate with your distributor or you will be chasing your own tail.

Puns intended.

Oh damn! Sorry about that. I got so wrapped up in the fuel system I forgot you'd linked to that thread.

Looks like that's just the info I need.

Is it necessary to replace the o-ring?

No worries. No, if the O-ring is in good shape, it's not really necessary. It's just that it's cheap and easy to replace. One of those "feel good" maintenance items. I actually put my old one back on because the new one I purchased didn't seem to fit right and was making it very difficult to get the dizzy back in place.

Sorry, a couple more things to note: you probably need to get some distributor grease. That's really the best thing to reapply after you clean out all the existing gunk. Also, make sure to grease up the distributor shaft where the points make contact on the cam. After I cleaned mine I don't think I lubed that sufficiently (or at all ) and I noticed my dwell wouldn't stay in the same place. Cap'n Krusty suggested that the pad on the points was wearing down quickly without the grease, and he's probably right. I think that solved that problem.

Thanks for the tip! I've got elec ignition though, so no points to worry about.

Other than that did you just grease between the two advance plates - like a grease sandwich? And then some on the ball bearing? Anywhere else I should hit while I'm in there?

I think that's pretty much it. A modest amount of dizzy grease between the plates and on the ball. Maybe put a drop or two of oil on the felt that comes out of the shaft. Check the quality of the ground strap between the two plates, too. That can cause issues if that's not making a good connection.

Good luck!

hi, maybe the below will help?

"Throttle Switch

by

Kjell Nelin

The throttle switch can be found mounted underneath the throttle body. To test, turn on the ignition and open the throttle with your hand. You should be able to hear the injectors firing, a sort of "brrrrrrp" noise. If working correctly, the injectors will fire 20 times for the full range of movement. One very mysterious intermittent
fault caused by the throttle switch is an occasional "bucking" while driving at constant speed. This is caused by the switch cutting of the fuel and then turning it back
on. Test by disconnecting the switch (it is amazing how well the car will run without it, actually), you will notice that acceleration will be a little sluggish as the
"accelerator pump" action will be missing. "

Aha! i finally got it. After a couple weeks or whatever of dealing with this, and after cleaning the dizzy, cleaning every electrical contact I could find, after replacing the fuel filter, and after thinking I had a bad intake air temp sensor, and having nothing permanently fix the problem...I finally figured the issue out!

I decided to clean all the multi pin connectors on the relay board today, and when I went to unhook the negative battery terminal, the clamp broke off of the main ground wire that connects to the chassis. There were probably only a couple wires of the multi core cable still attached to the clamp, which would've not been enough to handle the full current all the electronics needed. Probably on occasion the wire would move close enough to the connector to make decent contact for full power, and then move away again when I'd lose power.

Got a new connector on there and the car is GOLDEN! Full power under all driving conditions, and everything on the car seems to be working better.
Moral of the story: check the obvious shit first before diving into the complex stuff!

Amen brother!

But at least you learned a lot of things that could help later.

Geesh, thanks for posting the solution. That's probably a lesson learned for a lot of us! Glad all is now well.

Very true! Thanks to everyone that lent suggestions and help!