Intro 1972 Irish Green 1.7L; help needed with jerking engine Options

[andreic]

One more test done today -- I tried to run it with the TPS disconnected. It ran so poorly that I was not able to make it past the end of my block. A lot of backfiring was the main problem, but also it would not rev up past 1000 rpm.

I then reconnected the TPS. I don't know if it was this, or the fact that by that time some of the heat of the engine made its way to wherever it needs to (the engine runs better when warm), but afterwards I was able to drive it around the block and into the garage. Still running poorly, and with a couple of backfires, but not as bad.

To answer mepstein: fuel filter and all fuel lines were replaced less than 5 months ago, along with new fuel pump. The fuel pressure is very steady at 28 PSI, checked two days ago. I have a couple of coils lying around, I could try to use another one.

I don't know how to check the engine grounds. But if it were this, why would the engine be running better after warming up? The bucking was terrible this morning (much colder outside, in the high 30's).

[andreic]

One more thought. Could it be the ECU itself? Does anyone have a good one lying around that I could borrow, to try to switch mine out for a test?

[mepstein]

One more test done today -- I tried to run it with the TPS disconnected. It ran so poorly that I was not able to make it past the end of my block. A lot of backfiring was the main problem, but also it would not rev up past 1000 rpm.

I then reconnected the TPS. I don't know if it was this, or the fact that by that time some of the heat of the engine made its way to wherever it needs to (the engine runs better when warm), but afterwards I was able to drive it around the block and into the garage. Still running poorly, and with a couple of backfires, but not as bad.

To answer mepstein: fuel filter and all fuel lines were replaced less than 5 months ago, along with new fuel pump. The fuel pressure is very steady at 28 PSI, checked two days ago. I have a couple of coils lying around, I could try to use another one.

I don't know how to check the engine grounds. But if it were this, why would the engine be running better after warming up? The bucking was terrible this morning (much colder outside, in the high 30's).

Loosen all the brown wires attached to the engine, clean and reattach.

[IronHillRestorations]

I thought I read through all the posts, but I might have missed it.

Have you replaced the ignition components? Points, plugs, rotor, cap, condenser?

Have you checked the FI trigger points in the distributor?

[ChrisFoley]

The red mark you see on the front side of the fan is not a factory mark. With the engine not running, rotate the engine to where the mark is visible and verify it is in the correct location relative to the factory marks on the back side of the fan.
For reference, TDC is about 4 fins away from one of the heavy ribs, and 27 degree btdc is just a little more than one fin from the same rib.

You need to track down the hissing sound and make sure it isn't an intake leak.
With the engine idling, spray carb cleaner at each of the intake connections - at the plenum, at the heads, around the injectors.

[injunmort]

all suggestions are great, I would now swap coil, verify the timing and change condesor. it more sounds to me what you describe is somewhere the ignition is breaking down. timing coil and condenser.

[andreic]

OK, finally some progress. I noticed on the instructions on how to adjust the timing that someone commented that the vacuum lines should be disconnected when adjusting the timing. With them off, the timing changed quite dramatically, even at 3500 rpm. Readjusted it this way, and the car runs much better -- no more backfiring, fairly solid acceleration, very little hesitations.

I still have the "trailer towing" issue -- slight jerking at constant speed, more so on acceleration. But I think I figured that out too; I disconnected the TPS, and no more jerking! So I guess my problems were a misadjusted timing, and a bad TPS.

Three questions:

1) Where do I get a good TPS board to replace my worn one?
2) Is it normal for the vacuum lines to make such a big difference even at wide open throttle? My timing was off by probably 5-10 degrees (one whole rib on the fan) with the vacuum lines on versus off. I thought the vacuum lines were there to lower the idle when the throttle is closed, and to increase the advance on acceleration from idle. I simply wonder if my canister on the distributor works properly.
3) Sometimes the car idles at 1800 rpm (the first 10-15 minutes of driving), after which it settles to a 900 rpm idle when fully warmed up. Is this normal?

Thanks,
Andrei.

[mgphoto]

#3 normal

#2 vacuum lines are advance and retard, later versions have retard only. Timing with hoses attached subverts the internal mechanical advance.

#1 a few people here sell replacement circuit boards for the TPS, held in with a single rivet. Easy replacement, clean contacts and lube with Deoxit, than readjust.

ps: “trailer hitching” can be caused by an MPS that is not adjusted correctly, TPS has an idle circuit, when the switch transitions from idle to acceleration the MPS takes over, this transition is where the bucking starts and doesn’t end until the MPS senses hard acceleration.

[andreic]

Well, that was optimistic.... Sadly it turns out that that was not the problem. I let the car cool down for a couple of hours, and then being happy that it was fixed I thought I'd take it out for another spin. All the old problems were back with a vengeance: backfiring, low idle, trouble revving up past 1000rpm. Removing the vacuum lines makes the idle slightly higher, but nowhere near as much as before.

So my guess is that there is some intermittent problem somewhere. When it happens, the car runs like crap when cold, and even warmed up idles around 700 rpm with the current setting of the idle screw on the throttle. What I saw earlier today was one of the rare moments when it ran well -- good acceleration, no hesitations, no backfires, and an idle of 1800 rpm. Then something went bad again and it returned to its old habits.

This is driving me insane! Tomorrow I'll try to replace the condenser. Today I had put a new coil on it, so the coil is not the problem.

[72hardtop]

Check your fuel pressure. What you describe sounds like surging (lean condition).

Also check for vacuum leak.s.

[rhodyguy]

Is the strainer sock in the fuel tank in good, functional condition?

[mgphoto]

Head temp sensor lose, not screwed into the head tightly, or wire connector coming lose.

[914_teener]

OK, finally some progress. I noticed on the instructions on how to adjust the timing that someone commented that the vacuum lines should be disconnected when adjusting the timing. With them off, the timing changed quite dramatically, even at 3500 rpm. Readjusted it this way, and the car runs much better -- no more backfiring, fairly solid acceleration, very little hesitations.

I still have the "trailer towing" issue -- slight jerking at constant speed, more so on acceleration. But I think I figured that out too; I disconnected the TPS, and no more jerking! So I guess my problems were a misadjusted timing, and a bad TPS.

Three questions:

1) Where do I get a good TPS board to replace my worn one?
2) Is it normal for the vacuum lines to make such a big difference even at wide open throttle? My timing was off by probably 5-10 degrees (one whole rib on the fan) with the vacuum lines on versus off. I thought the vacuum lines were there to lower the idle when the throttle is closed, and to increase the advance on acceleration from idle. I simply wonder if my canister on the distributor works properly.
3) Sometimes the car idles at 1800 rpm (the first 10-15 minutes of driving), after which it settles to a 900 rpm idle when fully warmed up. Is this normal?

Thanks,
Andrei.

The second post.....did you inspect and clean the advance plate inside the dizzy?

Also......since you have the Mighty Vac.....if the advance diaphram on the dizzy leaks.....you have a vaccum leak AND your car will drive like crap. Also there is a ground wire on the advance plate....make sure it is intact.

So post a picture of the inside of your dizzy and test the diaphrams on the dizzy and report back.