A list of all things that could make a L-Jet Jerky, now with ............Pics of my troubled head Options

[jsayre914]

I have a great daily driver. 1.8 L motor with L-jet injection, and it jerks like a son of a %^$%. It has all new vacume lines, none of wich are leaking (idles smooth at 900rpm) i have blocked off the deceleration valve. It was not letting the idle come back down fast enough for my taste. New jugs rings pistons etc. It has new plugs and wires. a new resistor pack and a newer duel relay. new alternator and new voltage regulator. Valves adjusted .006/ .008 perfectly with new valve cover gaskets. It has a new fuel pump and fuel filter, and many new wiring harness. Injectors were all cleaned and new screens put in. It runs up to 5K with no problems and runs strong to about 110mph on a flat. (IMG:style_emoticons/default/driving.gif)


Whe i accelerate easy it starts to jerk the whole way. If i try to run in 2nd or 3rd it jerks the whole time even at constant speed. sometimes i will seesaw the clutch just so i dont look to embarrising.

What is the list of things to check (i want to check everything) but i feel like i checked it all and then rechecked it (IMG:style_emoticons/default/confused24.gif)


one other problem probably related, i cant keep constant power to the fuel pump through the relay, it chokes off sometimes and dosnt want to come back (PITA) so i jumped the fuel pump lead to the + coil for now. (dont be mad) (IMG:style_emoticons/default/rolleyes.gif)

[McMark]

I've had really good results from putting in a rebuilt AFM from Fuel Injection Corp.

[Brando]

Pull the black cover off of the Air Flow Sensor. Look at the carbon resistor tract that the arm wipes across.

Does it look pitted? Are there areas where you can see the white or green PCB through the black carbon?

This may help:
Rejuvenating a Bosch Motronic Air Flow Meter

[davesprinkle]

Make sure your rubber elbow isn't cracked.

[r_towle]

Check the advance plates on the distributor and the little ground wire.

Capn Krusty had a few new ones on the shelf, and George at AA also has new ones on the shelf.

Also the vacuum advance canister on the distributor can contribute to the problem...pull it off of the advance plates, remove it from the distributor and cap the vacuum line...the car will run fine without it for testing purposes...


Those issues do create a jerky car.
First I would replace the gaskets on the oil filler cap, there are three...a o-ring in the lid, a gasket in the lid, and the gasket under the base of the filler assembly.

Rich

[Bleyseng]

yep, either a sticking advance plate or vacuum leaks are the first things to look at.

[jsayre914]

I will have to pull the cover off the afm when the rain stops. I dont have a garage right now, it is full of boxes, since i sold my house. I will take a pic of what i see.

I am sure the huge elbow is not cracked, i took it off and cleaned it real good with armorall, it is perfect. and i thought i would have a real high idle if this was leaking. right?

as far as the distributor goes... i have never really taken one apart yet, not sure what theadvance plates look like, or how to tell if they were bad. same goes for the vacume advance. if i plug both lines going into it, how can i tell if this was the culprit?

thanks guys

[zonedoubt]

Sticky flapper arm on AFC. At one point, mine was actually snagging on one of the contacts and was bucking badly until I found the problem.

[jsayre914]

Sticky flapper arm on AFC. At one point, mine was actually snagging on one of the contacts and was bucking badly until I found the problem.

so how did you resole it?

wd-40

[underthetire]

I agree with the advance pate/advance springs/advance shaft. To test the vac can, a hand pump is the best way, available at HF pretty cheap and work well. You can also put a piece of hose on the nipple and suck on it, should move the advance/point plate, and it should hold vacuum. Also, on the top of the dizzy shaft, under the rotor, there is a small piece of felt inside the hole. Place a few drops of 3 n 1 oil or equiv. in there. WD40 is not a lubricant and should not be used in here. This will lube the mechanical advance. You should be able to grab the rotor with the dizzy in place and turn it about 15 degrees or so, and if you let it go it should snap back. If it does not snap back, the dizzy needs to come apart.

This is a good PM item to do even if something else is wrong.

[zonedoubt]

so how did you resole it?

wd-40

Nope. WD-40 didn't fix it. (IMG:style_emoticons/default/slap.gif)

Read here.

[jsayre914]

thanks for the pic, tell me more about what i am looking at. It looks like an alien space ship control modulator (IMG:style_emoticons/default/blink.gif)


is this what it should look like. or what part is not right. and wich way did you bend it.

sorry (IMG:style_emoticons/default/chair.gif)

[Katmanken]

That L-jet hates vacuum leaks...

And you can set up a resonance/surging condition....

So you need to check everywhere that can leak a vacuum between the air flap and the heads such as...

Manifold boots, injector seals. phenolic spacers on the heads, the oil fill cap seals, the cork gasket under the oil fill area, etc.

[jsayre914]

That L-jet hates vacuum leaks...

And you can set up a resonance/surging condition....

So you need to check everywhere that can leak a vacuum between the air flap and the heads such as...

Manifold boots, injector seals. phenolic spacers on the heads, the oil fill cap seals, the cork gasket under the oil fill area, etc.

thanks for the tips.

intake runner boots are brand new
injector seals are new big and small
spacers are new with a nice even bead of red silicon on both sides
cork gasket is new
all oil cap seals are new.

i replaced everything on this baby. (IMG:style_emoticons/default/smile.gif)

[zonedoubt]

thanks for the pic, tell me more about what i am looking at. It looks like an alien space ship control modulator (IMG:style_emoticons/default/blink.gif)

is this what it should look like. or what part is not right. and wich way did you bend it.

That's what's underneath the square black cover on the AFM. The way it look sin the photo is the way it's supposed to be. In my particular case, the contact with the dog-leg on the end was bent so that it occasionally got caught when the flapper opened up. Basically, this shut off the fuel to the injectors when fuel was needed most (e.g. more air coming thru the AFM). So under acceleration, it would bog down and go jerky.

It's worth a quick look under this cover to see how things work while manually pushing the flapper. Other than that, tcheck he usual suspects: vacuum leaks, timing/dwell, dizzy advance. Lots of good advice above.

I also used this site for troubleshooting my L-jet: http://manuals.type4.org/ljet/

[jim_hoyland]

I've had the jerky acceleration in my L-Jet too.

First time was caused by a loose connector at the base of the dual relay. The wire that runs the fuel pump was not getting full contact.

Second time, the oil vapor hose that connects to the Boot had come loose at the point of contact. Air was getting sucked in and causing big jerks in acceleration

A vac gauge and fuel pressure gause mounted in the engine compartment helped diagnose both these gremlins fast.

[ClayPerrine]

First off.. readjust your valves. The Haynes manual has a typo for the valve adjustment specs for the 1.8. They should both be .006. The .008 setting is ONLY for the sodium filled valves that came in the 2.0 heads.



In the picture, the #1 is the fuel pump contact. If you open the AFM flap, that is what turns the pump on. #2 is the wiper contacts that send the air flow information to the computer.

DO NOT ADJUST THE AIR FLOW METER SPRING TENSION!! It is calibrated properly for the engine, and takes a special tool to readjust. Been there, done that. I even own the tool to readjust them. I suggest that you don't open the air flow meter at all.

Check to see if the boot between the air flow meter and the throttle body is cracked. It will cause bucking if it is. Also inspect the harness carefully for broken or cracked wiring.

I agree with the distributor advance plate issue. Try this... disconnect the vacuum advance and retard lines and see if it still bucks.

[jsayre914]

OK

i rechecked the valves, alls well. I pulled the air flow meter open, everything was perfect inside, as far as i could tell. I then squeezed the spade terminals a little bit snugger at the dual relay, and cleaned all the connections. Ran the same (IMG:style_emoticons/default/dry.gif)

THEN.....
(IMG:style_emoticons/default/blowup.gif)

All of a sudden the loudest banging you ever heard comming from the driverside valve area (IMG:style_emoticons/default/headbang.gif) WTF happened. Car will not idle now and i dont even want to start it untill i have time to pull the valve cover and take a look.


(IMG:style_emoticons/default/sad2.gif)

[VaccaRabite]

Banging?
Like clatter clatter.

Or BANG BANG BANG?

Zach

[jsayre914]

more like clatter clatter