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

[andreic]

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.

[andreic]

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.

[rjames]

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.