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> Intro 1972 Irish Green 1.7L; help needed with jerking engine
andreic
post Oct 6 2018, 09:11 PM
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Hello,

some of you may remember me. After owning for several years a red 1975 1.8L 914, on which I reinstalled the L-Jet, got it to work well, and have sold this summer, I am now working on a 1972 1.7L D-Jet which I got this spring. Photos attached.

So far I got the brakes to work well (new front calipers from PMB were installed, and all four flex lines were replaced), replaced all fuel lines and the fuel pump, replaced all vacuum lines, new spark plugs, points, cap, wires and rotor. Also adjusted all valve clearances. I did a compression check and all was well, I got around 120lbs on all cylinders.

What still plagues me are two engine issues. One is that when the engine is cold, if I rev it up it will make a loud noise that sounds like a bad rattle. It is only there on hard acceleration, and it goes away almost completely as the engine gets warm, say, after 10-15 minutes. I have come up with several ideas what it could be: exhaust noise from badly sealing exhaust ports; valve noise; or something else in the exhaust (the muffler is an aftermarket one, and I am not sure if there isn't something in it rattling).

Another issue I have is that the car is not riding smoothly. It is hard to explain, but even if I am driving at constant speed, not moving my foot on the gas, it will jerk ever so slightly forward every couple of seconds, as if getting some extra power. The issue again is much more visible with the engine cold, but even properly warmed up you can feel it. It is stronger when accelerating than at constant speed; on acceleration the car really stumbles some times. When the engine is cold it can be pretty bad, enough that some times I worried if I would be able to climb a hill. I first thought it was ignition related, but after going through everything electrical I doubt it is this. (Replacing the spark plug, points, cap, wires and rotor changed nothing.) The car also seems a bit underpowered compared to my other one.

I am starting to wonder if the two things (the rattle and the jerking) are not related, and if it could be a valve issue. By the way, once or twice in the span of an hour's worth of driving I thought I heard a mild backfire.

Any suggestions on what could be the problem? Any help will be greatly appreciated.

Andrei.


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914Sixer
post Oct 7 2018, 07:35 AM
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Check the routing on the accelerator cable. Not uncommon to be kinked or wrapped around something in the tunnel. Pull it off the throttle body and check for operation. That is why 914Rubber has made new and improved ones.

Love the color
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JeffBowlsby
post Oct 7 2018, 08:08 AM
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'trailer hitching (jerking) may be caused by a worn out TPS. Inspect yours and if its worn, get the new board
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Wyvern
post Oct 7 2018, 09:37 AM
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Sounds exactly what I had with mine .
Did all the stuff you mention . every time i "thought" it got a bit better.

last 2 things I fixed did it.

The constant speed herkey jerkey was fixed by installing a new TPS board.
50% better!

Going one step deeper into the dizzy to get to and clean / lube the Injector fire points got me going as it should be.

I have since found that the contact at the injector has a very similar "feel" to it when not connecting well. When working on other stuff (engine running) just touching that connector I could hear that the injector would stop firing. I cleaned each injector connector and used a dental tool to bend the connector on the loom side ever so slightly to help make a good contact.
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Dave_Darling
post Oct 7 2018, 10:46 AM
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One test is to unplug the throttle position sensor. This way it cannot contribute to your problem. Acceleration will be noticeably worse, but if the car no longer jerks you have a very strong hint about where the problem may be.

The rattling noise could be pinging, but if it goes away when the engine warms up that is much less likely. Typical circumstances for pinging are a warm engine, mid-range RPM, and accelerating but throttle not open all the way. The pinging I have heard in my old 1.8 sounded kind of like a spitting rattle sound.

Backfires could be all sorts of things. My car developed an intermittent "soft" sounding backfire. Just once and it would go away for a minute or two, then happen again. Turned out to be the worst case problem; it was a valve seat popping out of the head and back in again. A compression check probably would have told me about it before it was a completely dead hole. Yours probably isn't this, but it's worth checking.

--DD
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andreic
post Oct 8 2018, 10:03 PM
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Ok, things are weirder than I thought. After going for a drive yesterday, this morning I looked at the exhaust pipe that coils around going to the muffler in the back of the car (I have an aftermarket muffler, possibly a Bursch). It was originally painted black, but now all the paint appears to have flaked/burned off, and there is some chalky residue on the pipe.

Also today I tried starting it again, to warm it up in order to check compressions. It ran very badly until it warmed up, barely idling, and occasionally misfiring, even with my foot on the throttle; it had almost no power even going down hill. After it warmed up it was slightly better, but still running uneven and almost dying at idle. After I shut it down it did a very loud backfire (it being dark, I even saw the burning gas coming out of the exhaust!).

I did not try to run it much, but did the compression test, which was fine - 120-125 psi on all cylinders, very even.

I am puzzled, because to me this sounds like it could be a timing issue. I thought I had adjusted the timing right. I will double check it again tomorrow, after I get a new timing light (my old one died right after I had got the timing to what I thought it should be). Or could it be running way too rich/lean?

One other odd thing. As the engine is running, especially at idle, I hear a loud hissing noise, as if air is being aspirated through a tight channel. My current guess is that it comes from the throttle body, and I am hearing it because I am running the engine without the air cleaner (all I have is the rubber piece coming off of the throttle body, and that is not connected to anything). Could this be right? The noise seems to come right from the intake manifold (the common black metal cavity from where the 4 intake tubes go to the cylinders).

Thanks.
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andreic
post Oct 8 2018, 10:09 PM
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Actually here is a newbie question. Unfortunately before disconnecting the ignition wires I did not mark them or take a photo of them. I am worried I may have misconnected them. How do I figure out which one is the #1 cylinder tower? I know there should be a marking on the distributor indicating roughly the TDC for cylinder 1, but I am not sure how it supposed to look like. (But perhaps the fact that the engine runs, albeit poorly, should mean that I connected them right.)
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JeffBowlsby
post Oct 8 2018, 10:54 PM
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Fire coming outta the tailpipe usually means RICH. Hard starting could also mean RICH.

Have you checked your CSV to see if its leaking fuel into the air plenum (thats what you called the 'intake manifold' above), at any time other than cranking.

Checked your fuel injectors for leakage and even flow? Pull them and shoot them into cans or glass jars while cranking to test.

Does your MPS hold a steady vacuum or does it leak down under a vacuum?
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injunmort
post Oct 9 2018, 04:03 AM
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have you checked timing. running hot like that suggests the timing is way out. the engine cooling tins are stamped with cylinder numbers and firing order.
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nditiz1
post Oct 9 2018, 06:52 AM
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I am having a similar engine jerking, trailer hitching, effect as well. I have been chasing this issue for awhile now and went over everything in the system without finding the answer. I removed the TPS connector and it didn't fix the jerking. I am getting popping in the exhaust on decel as well. Can't figure it out. Hopefully if you find your solution it will work for me as well. I'm going to double check the injector plugs as I know I have been plagued by 2 previously.
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andreic
post Oct 9 2018, 03:18 PM
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Here is a photo of the exhaust pipe with white residue and no paint left. I just realized that the residue may simply be leftover engine degreaser from when I cleaned up the engine a few days ago.

I will recheck the timing today, and try to go for a drive with the TPS disconnected to see if it makes any difference. I am more concerned about the backfiring, honestly.


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andreic
post Oct 9 2018, 03:26 PM
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Hi Jeff,

I don't know if the CSV leaks, but taking it out is a pain so I'd rather try it later. A while ago (at the beginning of summer) I checked and none of the injectors leaked. Of course, at the time the engine was running quite well, so they could have gone bad since then.

How do I check the MPS for holding vacuum? Can I just suck on the pipe going to it and feel if it loses vacuum?

The thing is that while the car was not running very well before, after washing the engine and changing the vacuum lines, coil, distributor cap, rotor, and points it runs much worse. In particular, before it was not backfiring at all. So my guess is that it is something related to what I recently did, and I did not touch the injectors or CSV.

A.

QUOTE(JeffBowlsby @ Oct 8 2018, 11:54 PM) *

Fire coming outta the tailpipe usually means RICH. Hard starting could also mean RICH.

Have you checked your CSV to see if its leaking fuel into the air plenum (thats what you called the 'intake manifold' above), at any time other than cranking.

Checked your fuel injectors for leakage and even flow? Pull them and shoot them into cans or glass jars while cranking to test.

Does your MPS hold a steady vacuum or does it leak down under a vacuum?

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rhodyguy
post Oct 9 2018, 03:35 PM
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MPS-buy a Mityvac

Remove the dist cap. Look for a mark on the top edge of the dist body. That should be number 1. The cyl are numbered on the tin. Verify #1 position with the mark on the fan. Consult your Haynes manual.
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rjames
post Oct 9 2018, 04:14 PM
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QUOTE
after washing the engine and changing the vacuum lines, coil, distributor cap, rotor, and points it runs much worse


As others have said, check the timing. Also if you changed the points make sure the dwell is set correctly. Verify vacuum hoses are connected correctly. (search the site for a picture of where they go).

How did you was the engine? Did you "wash" the top side? You may have an electrical short somewhere if electrical components got wet.

Great looking car, btw. I'm probably the only one who is not a fan of Irish Green, but I like it on your car, especially with the painted bumpers.
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andreic
post Oct 9 2018, 10:23 PM
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Well, I checked a few things today, but found nothing. Here is what I did:

a) Bypassed the CSV with a length of hose going straight from the right rail to the left. Running the car made no difference -- same exact behavior: very rough idle when cold (the red alternator light comes on); pressing the gas pedal barely makes it rev up, a lot of stumbling, until it hits about 2500 rpm, when it takes off and revs up normally. After it warms up it runs better, less stumbling but still some. Some of the stumbling definitely feels like backfires. So I don't think the CSV leaks.

b) Tried starting it with all injectors disconnected. Not a single time did it fire. So I don't think I have leaky injectors, at least not serious leaks.

c) Re-checked fuel pressure. Perfectly steady at 28 PSI, revving or not. I think that's what I want, right?

d) Re-checked the timing. With a timing light, at 3500 RPM (and after that) I can see a red line in the little window (V-shaped cut) in the fan housing. I think that is what I want.

e) Checked the ignition wires according to the instructions above, and they seem to be right. The front left tower on the distributor goes to the rear left cylinder (#1), the rear left to the front left cylinder (#2), the front right to the front right cylinder (#4) and the rear right to the rear right cylinder (#3).

I guess the next step would be to check the MPS. How does one check it? If it is bad, would that explain my problems (probably running rich, backfiring, trouble accelerating from idle when cold)?

Maybe I should also check the CHT sensor and/or the air plenum temp sensor? How does one do this?

When I washed the engine I sprayed degreaser over all of the engine, let it sit for 15 minutes, then rinsed with a soft mist from a garden hose. I agree some electrical stuff may have gotten wet, but by now (and with a very hot engine compartment -- driving it for an hour or so) everything should have dried, I guess?

Thanks.
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914_teener
post Oct 10 2018, 08:25 AM
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Couple of things come to mind:

First check the MPS as others have already posted. The procedure is on the Anders site.

Also, there is a lead (wire) to the CHT. This lead must be firmly connected and clean. Check that connection. The stock connector gets old and opaque.

If the ECU does not see a clean ground to the CHT then it CAN cause this. If it is not connected the engine will not run.

Check those two things and report back.

Be methodical. If you hear hissing...sounds also like a vaccum leak, take a hose to your ear and try to locate it.

Troubleshooting is an old skill, takes time.
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rjames
post Oct 10 2018, 12:04 PM
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QUOTE(andreic @ Oct 9 2018, 09:23 PM) *

Well, I checked a few things today, but found nothing. Here is what I did:

a) Bypassed the CSV with a length of hose going straight from the right rail to the left. Running the car made no difference -- same exact behavior: very rough idle when cold (the red alternator light comes on); pressing the gas pedal barely makes it rev up, a lot of stumbling, until it hits about 2500 rpm, when it takes off and revs up normally. After it warms up it runs better, less stumbling but still some. Some of the stumbling definitely feels like backfires. So I don't think the CSV leaks.

b) Tried starting it with all injectors disconnected. Not a single time did it fire. So I don't think I have leaky injectors, at least not serious leaks.

c) Re-checked fuel pressure. Perfectly steady at 28 PSI, revving or not. I think that's what I want, right?

d) Re-checked the timing. With a timing light, at 3500 RPM (and after that) I can see a red line in the little window (V-shaped cut) in the fan housing. I think that is what I want.

e) Checked the ignition wires according to the instructions above, and they seem to be right. The front left tower on the distributor goes to the rear left cylinder (#1), the rear left to the front left cylinder (#2), the front right to the front right cylinder (#4) and the rear right to the rear right cylinder (#3).

I guess the next step would be to check the MPS. How does one check it? If it is bad, would that explain my problems (probably running rich, backfiring, trouble accelerating from idle when cold)?

Maybe I should also check the CHT sensor and/or the air plenum temp sensor? How does one do this?

When I washed the engine I sprayed degreaser over all of the engine, let it sit for 15 minutes, then rinsed with a soft mist from a garden hose. I agree some electrical stuff may have gotten wet, but by now (and with a very hot engine compartment -- driving it for an hour or so) everything should have dried, I guess?

Thanks.


very rough idle when cold : check AAR valve. It doesn't change the mixture but should give a high idle when the engine is cold.

Timing: In depth write-up if you haven't already read it is here:
https://www.pelicanparts.com/techarticles/9.../914_timing.htm

MPS needs to hold vacuum.
get a mity-vac and pump it up to 15hg on the gauge and leave it for 5+ minutes to see if it leaks.
Also test pins # 7 to # 15 and the resistance should be 90 ohms. # 8 to #10 resistance should be 350 ohms.
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GregAmy
post Oct 10 2018, 12:27 PM
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"help needed with jerking engine"

Am I the only one to come in here to find out how to jerk an engine...?
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andreic
post Oct 10 2018, 09:37 PM
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OK, still no success. I checked the MPS, and it holds vacuum like a champ (15 mm Hg and the needle did not move at all over 5 minutes or so). The resistances at the 4 pins were 90 Ohms and 300 Ohms (more or less, my analog ohmmeter is not very accurate).

I also checked the CHT. Cold, the resistance was around 1900-2000 Ohms (at around 65 degrees outside). The connectors looked to be in very good shape.

Re-checked one more time the timing, looks very good.

Took the car out for a spin -- it runs better (no more backfiring), but the problems still persist. "Trailer towing" at all engine RPMs (jerking uneven running), and when cold does not want to rev up at low RPMs, seems to fall on its face. Warmed up the revving problem at low RPMs goes away, but the uneven driving persists. Tomorrow I'll give it a try with the TPS disconnected and report on what I find.

More suggestions on what to check?
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mepstein
post Oct 11 2018, 03:19 AM
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Fuel filter
All engine grounds
Coil
New fuel lines on the engine.

BTW - the bucking on mine was so bad, it wasn’t drivable. I almost gave up on it. Unfortunately, since I was making more than one change at a time, I can’t be sure what caused the issue but once it was fixed, the car became very enjoyable to drive.
Don’t give up.
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