Firstfives.org

Hello all! New-ish member fro Oslo!
I have discovered that there are a lot of L-Jetronic knowledge here, so I have to consult you in a very important question! javascript:emoticon(':oops:') I have mounted a reconditioned M30, 3.3 L-Jetronic (1978) in my 68 2800CS e9. After a lot of failing and testing I managed to start the engine. But the exhaust manifold gets red hot very quick!
I have checked that the distributor mark is at about 3:30 and that the rotorcap points to this. (and plug no. 1)
The following are observations after starting the engine:
- Realtively normal speed after starting cold engine
- Veeery slow reaction when pushing the gas pedal, goes veeery slowly back to normal idle.
- Pre-ignition is about 22 degrees at 1000 rpm. (supposed to be 22 degrees at 1650 rpm). Incandescent manifold!
- Have suspected that there is an air leak in the inlet manifold, but has disproved this after a lot of checking.
- I have also made an air leak to see if the speed increases, but it decreases ... contrary to what I thought was going to happen.
- Idle screw is almost completely closed
- Has increased the ignition angle and the result has been much higher idle, faster throttle response and faster reduction of speed when the accelerator pedal is released, but still red hot manifold and exhaust.
I´m pretty shure that the camshaft correspond with the crankshaft, but is it a way to check this without removing the timing case cover?
Anybody have an idea of what this engine suffers from?

Im also newish member here, so please take what ever I'm saying with a grain of salt....

But I did experience this too. I found that this was happening at IDLE.

The mixture, I think was too lean, causing the manifolds to get red-hot.

I adjusted the allen-bolt mixture screw on BOTTOM of AFM
(not the idle speed screw).

If I remember, there was a small black cap covering this screw.

So basically, I unhooked air filter box from AFM, tilted AFM 45 degrees, and adjusted screw while car was running.

BMW had a device to see if mixture was correct, but I did it by ear (does it sound funny if you turn one way too much?) and watching if my manifolds were getting hot (it was dark out).

My friends have used a "color tune" plug, I wonder if that would be any good for this....

Maybe that is what you have going on?

Welcome to the group!

If the exhaust manifold is too hot it almost has to be that the timing is too far retarded or too late. Is there a chance you are checking the timing with the TDC (top dead center) mark and not the 22 degree timing mark on the flywheel? As far as exactly where the distributor is pointed, that is pretty vague when we're talking a few degrees, after I've had an engine apart I just use that to get it close enough to start, then go to the timing light. You are using a timing light on the flywheel on the #1 cylinder, correct?

I have also been thinking about the AFM air mixture screw. Right now it is adjusted to the bottom. Does that mean that there is no air bypass?
If the mixture is lean, as i believe it is, an adjustment will make it leaner. Correct me if i´m wrong!
I use the vibration damper as reference (automatic gearbox) TDC mark correspond with the mark on the timing case. A small "wart" on the vibration damper also correspond with a timing device near the timing mark. I guess the angle between the TDC and the "wart" is 22 degrees. But I have to recheck it later. I also use stroboscope on cylinder no 1.

Have removed the valve cover and have been able to inspect that the camshaft is positioned correctly in relation to cranckshaft, it was actually very easy to check (as usual I found the recipe online).
-Also checked the vibration damper sitting in the correct position relative to the cranckshaft. (It is possible to set this wrong since it´s bolted on the end flange on the shaft) TDC shall correspond with the keyway on the crankshaft. Have found that TDC on vibration damper and TDC on flywheel corresponds so I guess it correctly. In addition, both lobes on cylinder # 1 almost straight down when it is at TDC. Hopefully this is right…
So now I hope that there are no more mechanical components that can create problems for the ignition!
I have checked and calibrated, both limit switches and damper in the throttle housing (thanks to Peter Florance) Idle screw is however almost completely closed, so I'm considering to open it some turns to a more normal "operating position"
AFM is a bit dodgy to me, but what can go wrong? Is the censor that sends signals to the ECU destroyed?
ECU works correctly?? Bought it on ebay and have no idea if it works properly
This will be a long weekend in the garage.

Henrik wrote:I have also been thinking about the AFM air mixture screw. Right now it is adjusted to the bottom. Does that mean that there is no air bypass?

I asked this question recently. The answer is that the more you back that screw out, the more bypass air allowed, and hence the leaner the idle. So it sounds like you should have a lot of bypass. The O2 sensor and the lambda feedback system (if you have this system) should be trying to hit a preordained air-fuel target, so I guess it is debatable if this screw does much. It might just make it closer or farther from the target, and thus harder/easier to compensate.

Henrik wrote:Have removed the valve cover and have been able to inspect that the camshaft is positioned correctly in relation to cranckshaft, it was actually very easy to check (as usual I found the recipe online).
-Also checked the vibration damper sitting in the correct position relative to the cranckshaft. (It is possible to set this wrong since it´s bolted on the end flange on the shaft) TDC shall correspond with the keyway on the crankshaft. Have found that TDC on vibration damper and TDC on flywheel corresponds so I guess it correctly. In addition, both lobes on cylinder # 1 almost straight down when it is at TDC. Hopefully this is right…
So now I hope that there are no more mechanical components that can create problems for the ignition!
I have checked and calibrated, both limit switches and damper in the throttle housing (thanks to Peter Florance) Idle screw is however almost completely closed, so I'm considering to open it some turns to a more normal "operating position"
AFM is a bit dodgy to me, but what can go wrong? Is the censor that sends signals to the ECU destroyed?
ECU works correctly?? Bought it on ebay and have no idea if it works properly
This will be a long weekend in the garage.

It isn't possible to bolt up the crank dampener incorrectly, the bolt holes are not a symmetrical pattern. But you already confirmed that anyway. The AFM is the primary input to the ECU for mixture, but I'm still convinced it's a timing issue, not mixture. The air bypass in the AFM really only plays a part at idle. AFMs do go bad but mostly because someone tinkered with it. If the exhaust manifolds are glowing red hot it's timing.

I also believe that it still has to be the timing in one way or another, but it is possible that the ignition adjustment on these engines are so sensitive that only a tiny deviation can cause these problems? I have just ordered a timing light with rpm. for more accuracy. Maybe this can help?
As part of the elimination regime I am in now I think I also take a quick peek into the AFM.

No, they are not all that sensitive. I used to run more advance than spec'd because it seemed to run better. One time with an E3 I used to have I ended up with a very retarded situation as the arm for the vacuum control popped off and got wedged in an odd way. The car ran hot, ran poorly, but still no glowing exhaust manifolds.

The engine is about 35 years old. It had only 100 000 km on the road before the car was scrapped because of illegal imports. I gave it a complete overhaul when I bought it, but did nothing with the injectors. It may be possible that they do not supply enough fuel due to dirt in the nozzles. This may explain a lean mixture and then again hot exhaust. May be I should test the fuel nozzles before I go any further?

I still don't think running lean would make the manifolds run red hot. Remember what late or retarded timing does, it delays the ignition point so much of the combustion is still taking place when the valve opens and it continues while it's in the exhaust manifold.

I completely agree with you Mike, and I think the solution to my problem consists of several factors. Ignition is obviously completely wrong since it has been impossible to adjust it precisely because of varying speed and heat. On the other hand, I ask myself how this heat is developed, and I can't think otherwise than that the combustion in the cylinders is very poor due to poor atomization of the fuel. Combustion has a longer interval in the cylinder and extends into the manifold even when the cylinder enters a new cycle. This may also explain why the engine rpm. responds very slowly when I increase throttle and decreases very slowly when I reduce throttle. It is also an abnormally low vacuum in the intake manifold. What I do now (which I should have done anyway) is to take out all the fuel injectors and send them to overhaul.

Hopefully the answer is that dirt may have clogged nozzles and provides poor atomization.

Does your engine have timing matks on the flywheel at the rear of the engine near the starter? I dont use the damper at all when timing.

Yes it´s timing marks on the flywheel, but they are hard to locate. It´s an automatic and the flywheel is thinner than the one with manual box. Looking forward to collect the fuel injectors when they are tested. Hopefully they are the source to my problems. If not I´m completely out of ideas to solve this mystery.....

Fuel injectors installed after testing and cleaning. No difference, still hot exhaust pipes. I have checked all TDC and camshaft alignments and they are also spot on. To avoid interference from Auxhiliary Air Valve all connections are blinded with tape. Distributor position with vacuum cone almost pointing at 12 o´clock when cylinder one at TDC. Location mark in the lip of the distributor approx. at 3:30. Is it correct that the distributor cap should point straight at this location?

After start up, and when engine is in normal operating temperature the idle is very high. About 1800-2000 rpm. Could he ECU be the problem, feeding to much fuel?