Intermittent idle and engine roughness

[meinster]

Truncated. Refer developments at the end of this posting!

[meinster]

Truncated. Refer developments at the end of this posting!

[Hvydtox]

You could take out the injectors and send them to RC injectors in southern california and they will clean them and balance them for about thirty bucks apiece. Make sure the valves are adjusted. After making sure your distributor shaft is not worn and the fuel pump pressure is ok, you can get an inline fuel pressure gauge from summit to make sure it is up to spec. If all fails and you love the car you will have to pull the computer system and put in double webbers for four hundred bucks. Fred

[coconut 321]

Pete; I have the same system, L-Jetronic, on my '74. Your problem looks to me to be electrical, which means that you should check all terminals on the wiring harness for continuity, especially the grounds. Also check the wiring for continuity especially the Cylinder Head Temperature sensor located at cylinder #3. It determines the richness of the fuel mixture by resistance. At 68 degrees the resistance should be 2000 to 3000 ohms, at 122 deg. it should be 700 to 1000 ohms. Good hunting.

[meinster]

Truncated. Refer developments at the end of this posting!

[meinster]

Truncated. Refer developments at the end of this posting!

[billswim]

My first post as I'm usually too busy working on the cars to surf but...I'm the one working on th car and sadly, I'm stumped! I'm not unfamiliar with 914s and have checked what I think is just about everything.

The problem is the engine is running too rich. My first guess was a poor ground. They checked out fine and then I bypassed them straight to the (-)battery just to be certain and the problem was the same. The cyl head temp sensor was next but it spec'd out perfect. No vacum leaks. No odd running/change when each electrical connection was wiggled. The ballast resistors were traded with a known good set and still the same. I thought the main/double relay was clicking more than it should but it ddn't have any effect on the car's running. Fuel pressure was a little high at 40 psi without vacum on the regulator, so I installed an adjustable unit and ran it all the way down to 20 psi and still the same. The cold start valve plug was checked and then I ran a separte fuel line around the cold start valve to make sure it wasn't pouring additional fuel into the engine. Still the same. I tried three different ecu's, same.

What I have determined is that all four injectors are firing at EACH ignition event and to my understanding they should all four fire at EVERY OTHER event. I have never run into a problem such as this. I am just now looking in my stash for a good used wiring harness to try and swap in as I have checked every other thing I can possibly think of. Also checked the tps to make certain it wasn't giving the full throttle signal.

Anyone run into this before?

[meinster]

Truncated. Refer developments at the end of this posting!

[Dave at Pelican Parts]

Sorry, but your brother is used to dealing with more modern cars. The 914's L-jet ECU does not have a "limp home" mode. I am not sure that it can simply be swapped out for an aftermarket one, either. (I know the D-jet cannot; not so sure about the L-jet.)

--DD

[meinster]

Truncated. Refer developments at the end of this posting!

[billswim]

Pete,

Pretty sure I got it. Call me, the phone # you left isn't working.

[Dave at Pelican Parts]

I'm still trying to think through it...

--DD

[Tobra]

This is sort of random, but have you checked to see if the little door in AFC deal moving freely, had it happen on an L jet bug. Makes it run pig rich if it sticks open and hot like a MF'er. Tough to diagnose as it was sporadic, but tended to happen after highway runs, when door was wide open, apparently it would hang up. You can check the electrical side too with ohmeter, but years of use allow for an accumulation of gunk.

Just got a midamerica catalog that listed remanufactured FI stuff for VW, which may give an option if it is hosed in your car, were like $150 for the AFC I think.

[meinster]

I am leaning toward having a Porsche bonfire!

OK, do you mean by AFC, the Intake Air sensor? Your question is not random at all, that is one of the items in the chain that could suffer failure. I appreciate your input!

What you are describing sounds as though it's similar, on my drive home she actually started her issues again... as I slowed for traffic on the highway, depress the clutch... poof! Engine dies, when I got off the highway, she was doing all her usual spluttering, smoking and no idle. The problem does seems to diminish when I get the RPM up, however that is difficult to tell because she is overfuelled, so there is still a certain amount of smoke! So once again not dissimilar from what you describe... however here is what we have done again, with some additions, you'll see we actually checked and rechecked and re-substituted that Intake air sensor (Air Flow sensor) with a reconditioned one.

The problem
- The engine is running rich, no idle, smoke and all round pain in the a$$!

We looked at
- Grounding on wires and general connectivity. Found to be satisfactory.
- CHT sensor checked found sattis but replaced nonetheless!
- No significant vacuum leaks.
- Ballast resistors were swapped out with known good ones, originals found to be sattis.
- The main/double relay was clicking more than it should but it didn't have any effect on the car's running.
- Fuel pressure was a little high at 40 psi without vacuum on the regulator. Installed an adjustable unit, it went down to 20 psi and still the same performance issues.
- The cold start valve was checked... ran a separate fuel line around the cold start valve to make sure it wasn't pouring additional fuel into the engine. Found to be sattis.
- Substituted three different ECUs, Original found to be sattis.
- Throttle body itself was examined and was found to be sattis.
- Checked the throttle position sensor (to make certain it wasn't giving the full throttle signal) - found to be sattis.
- We replaced the original Air flow unit, subsequently, Bill even swapped in a second one - Still no bloody improvement!

Bill's question
- "What I have determined is that all four injectors are firing at EACH ignition event and to my understanding they should all four fire at EVERY OTHER event".

Do you think that could be indicative of the problem?

With the money I spent thus far, I could have performed a carb conversion! My head still hurts, and I know for a fact that Bill is about to take her out back and set her on fire, if I don't!

This car is becoming the bane of my existence! I am studying and need transport, now I am stuck spending money I can't afford to spend on a car that's just not co-operating!

Bill, do you think we should consider a carb conversion? Do you have some old carbs and manifolds lying around? Otherwise we may have found a use for all the combustibles in your shop! I'll see you on Monday.

[meinster]

Oh... on a lighter note; 914's are now called "Portles" (cross between a Porsche and Beetle)... I have only ever had this much trouble with my Beetle back in SA! Roadholding means nothing if she won't go on the road!

Apologies if I offend any avid 914 supporters, but my experiences thus far are bordering on the ridiculous and actually lean toward my renaming this car "Hitler's Revenge".

Pete

[meinster]

If I disconnect the vacuum hose from the pressure regulator then she idles... barely, but it's more than I would have with that connected! Those relays that are located near the pressure regulator are clicking very loudly! Sounds odd. But that's been mentioned before!

Don't know if that helps, but that is what I have.

[Dave at Pelican Parts]

AFC usually stands for "Air-Flow Controlled", which is what Bosch called L-jet EFI early on. I think he means the Air Flow Meter, though--that's what has the flap in it that can stick.

Disconnecting the hose from the fuel pressure regulator will do two things: It will raise the fuel pressure (enriching the mixture), and introduce a lot of unmetered air into the intake (leaning the mixture). It probably leans it out more than it richens it though.

Have you been able to get the car into its "failed" state and make tests? E.g., what is the fuel pressure doing when the car is spluttering and misbehaving?

The injectors should indeed be opening every other ignition event, not every one. Do they do that both when the engine is misbehaving and when it is running well?

The relays clicking a lot is not a good sign. I'm not sure which ones are the ones by the pressure regulator (you mean the ones on the relay board?) but none of them should be clicking. The voltage regulator will, as that is how it works, but I don't recall really hearing that back when I had a stock VR.

The double relay should not click while the car is running--it should click once when the ignition comes on (which sends power to the ECU), and once to turn the fuel pump on.

You can ditch all of the round relays on top of the relay board; they are not needed for the 1.8s EFI. (Only the one for the heater blower motor is used, and the rear-window defroster if you have that.)

I'm still leaning toward an electrical problem...

The ECUs very rarely fail, but maybe in this case??? Oh, speaking of cases, what does the box for the ECU look like? Holes rotted in it? Tire marks on it? Clean and pristine?

I don't have much in the way of L-jet parts in my stash, but I probably have an extra relay board around. Making time to get it up to the East Bay (I'm assuming that's where you are, as Bill's location is listed as Oakland?) is pretty difficult in the near future. Hmm....

--DD

[Tobra]

Yeah, you take the air cleaner off, and can access the little flapper door, more open=more air=more fuel. I seem to remember the resistance goes to infinity when door is open and is zero when it is closed, but will have to check that one, it is in the shop manual I believe.

You can determine if you have an air leak by diddling with the idle screw. Turn the screw, no change in idle means air leak, somewhere.

[meinster]

Dave,

Yeah... we checked the Intake Air Sensor, though the symptoms are similar to what Tobra desribes, the unit seems to be functioning.

Whilst in the shop, she was permanently in her problem state, all checks performed were accomplished at that time. We spotted nothing that could cause this problem in itself! As stated there is an audible noise from the relays, but that does'nt seem to be affecting the performance, however will check again by substitution on Monday. The fuel pressure was on the high side, but also there, once we replace the fuel pressure regulator with an adjustable one, we found no improvement, so we reinstalled the old one!

I'll confer with Bill about the injector timing, in my Haynes book it stipulates the following... " At every second point opening (one full revolution of the crank), the control unit triggers all four injectors at the same time, but only half the required fuel is delivered per injection, therefor during every power cycle (two full crankshaft revolutions), two injections occur. Engine speed data is fed to the Control Unit from the rate of opening of the breaker points"

Both Dave and Bill were correct in the assertion that the injection cycle is incorrect, what could cause this?

This tells me (with my limited knowledge) that if it were a mechanical problem it could be the distributor itself that has odd play - not sure if that would be intermittent though, otherwise the metering of fuel per injection cycle is botched, this could be from a buggered Intake Air Sensor that has already been checked!?

The Control Unit looks like all the components in the car, it is 33 years old and a little weathered, however, we substituted other ECU's in there, with no improvement! It is next to the battery though, some serious corrosion there, thus the ECU may have been contaminated by acid?! The noisey relays are on the battery side as well!

We have attempted diagnosis by subtitution of many various components, few of those components we substituted are new, and may be giving similar problems... is there a reference on this site to proper electronic diagnosis (with multimeter) of the various components? My Intake Air Sensor has six pins!

I appreciate everybody's suggestions thusfar, the problem of course is one that causes secondary issues (extreme plug fouling being one of them - which begs the question, what are my valves going to start looking like if I keep running her like this?) so the sooner I can dispatch this issue, the sooner I can live happily ever after!

Thanks again
Pete

[Dave at Pelican Parts]

According my my understanding, the car should be opening all four injectors once per engine revolution (twice per distributor revolution). It sounds like yours are opening twice as often, which would result in a very rich mixture!

Oh, the relay board would be loaned for troubleshooting. (If it turns out that the board was the problem, then we can talk about you keeping it. )

There are L-jet articles available on the http://www.type2.com website: http://www.type2.com/library/fuel.htm

--DD