Any L-Jet Gurus? Trying to save '84 318.

[akimball442]

Good morning

I have an 84 318 I'm trying to resurrect. We already have another clapped out 318 that runs just fine, and probably has in excess of 300K miles.

This one is pretty nice, but it sat for more than half of its life. The stickers in the window indicate it was last registered in 2001.

I've owned several vintage Mercedes, VWs, and the other 318, and haven't really struggled to work on them or keep them running. I'm a diesel (heavy truck) tech by trade.

The fuel system in this car was a mess, and I get the impression from the lady I bought it from that it probably quit running sometime before it was parked. I drained the fuel and got it to cough and hiccup a few times, but that was it.

I have replaced the fuel tank, changed the in-tank pump, and replaced the filters. All 4 injectors were plugged, I was able to clean 2 of them, but I ended up replacing those too.

The plugs are new, cap, rotor, basic tune-up all done.

The car will start and idle, but it runs terribly, and is excessively rich, like a carburetor with the choke stuck shut. We're talking lumpy idle, and eye burning smoke.

Idle speed is, of course, too fast.

Fuel pressure at idle is 40 PSI. Disconnecting the vacuum line from the regulator increases pressure 5-6 PSI, indicating that it's working.

Temp sensors check out. The cold start valve doesn't work at all, but I've left it unplugged anyway, the point being that it isn't leaking fuel into the intake and isn't the problem.

The O2 sensor is disconnected. I've run many old Bosch systems this way, no problems, they're pretty happy in open loop. Reconnecting it causes it to run worse than it already deos. I assume it needs a new one, and I have one coming, but I know this should run ok in open loop. If it doesn't run well in open loop it'll never run well in closed loop.

Can anyone think of a reason this car would run so excessively rich? Pinching off the fuel line and dropping fuel pressure down to 5PSI or so lets it run smoothly, but obviously that's not the reason.

I believe the injectors are being commanded to too high of a duty cycle, but I wouldn't know what would cause that, especially in open loop which I assume should use some sort of fixed value.

I do have the other 318 to swap parts from, but I'd like to know if I'm overlooking anything obvious.

Thanks

Aaron

[dworthy]

Welcome to the Forum!

Unplugging the oxygen sensor will make the fuel map very fat, thus it will run rich. I would see about swapping the AFM from the good car, for if the old one is crap and the sweep is worn out, that too can cause a rich running issues. Also there is an adjustment hex on the AFM, if it's been monkeyed with, same thing too rich or too lean as it's an air bypass.

[akimball442]

Thanks for the reply.

I know unplugging the O2 sensor will cause rich running, but it shouldn't be terrible, just typical open loop which is slightly rich. I've run different Bosch systems (including our other 318) with the O2 disconnected for a long time with no ill effects. Improved fuel economy was the only big improvement once I finally replaced the O2 sensor in the other one. It was shorted and the car wouldn't run at all with it plugged in.

This morning, went out to the 'good one' and disconnected the ECU. Using the wiring diagram, I took values from all of the terminals that I could, from the harness side. I then went and compared those values with the ones from the 'bad' car. The readings were nearly identical. The Throttle/WOT switch is working perfectly. Power and grounds were good. Reading from the coolant temp sensor was as expected on both cars.

I did not perform a continuity test on any of the wires between the ECU and the AFM, which will perhaps be my next step- because...

I swapped the AFM from the 'good' car to the 'bad' car and it showed no change whatsoever. I then swapped the ECU from the 'good' to the 'bad' car, and there was no change.

I think I will check for contiunity for the AFM wiring harness, to make sure there are no issues there. But then again, the 'good' car will start and idle with the AFM sitting on the floor next to the car.

I do know that my fuel pump is a generic one, and probably isn't correct. I have ordered a complete in-tank pump assembly. But my instinct here is that these systems really just need correct fuel pressure to run, and the fuel pressure at the rail is at the spec of 40PSI which is indicated in the manual.

I suppose another test would be to dust off the old shop scope and compare the injector duty cycle between the two cars, but in open loop I'd think it should be a fixed value, especially in this 'dumb' system.

A final possibility is that the injectors I purchased are just plain garbage, and the flow rate is 10 times what it should be.

[323i E30]

(…)
A final possibility is that the injectors I purchased are just plain garbage, and the flow rate is 10 times what it should be.

Good point.
Are the ones you bought supposed to have the correct specs though?

[sienayr]

I had similar rich-running and poor idle problems when I purchased incorrect 19# Ford injectors to pair with the Miller MAF & 19# injector chip. After going through many of the same gyrations you have I finally got a new set of injectors (this time straight out of an M20 so I knew they were the right ones) and all was right with the world.

[Sunnyledge]

If the catalytic convertor is failing/obstructed it can result in a rich mixture.

[akimball442]

I had similar rich-running and poor idle problems when I purchased incorrect 19# Ford injectors to pair with the Miller MAF & 19# injector chip. After going through many of the same gyrations you have I finally got a new set of injectors (this time straight out of an M20 so I knew they were the right ones) and all was right with the world.

Here's to hoping! I am going to swap the injector rail out of the running car tomorrow. I ordered some new O-rings that I have to pick up in the morning.

- - - Updated - - -

If the catalytic convertor is failing/obstructed it can result in a rich mixture.

I removed the converter right away, it had an aftermarket one that was cracked.

[akimball442]

Well, it appears the injectors were the culprit. Damn Ebay!

It doesn't exactly run well, but it will at least run well enough to be in the same county with it, and try to sort out the other issues.

[323i E30]

Nice!

[dworthy]

If you still have the old set, send it out to these guys to get cleaned: https://www.rcfuelinjection.com/

They can clean and balance the injectors for you, even replace the o-rings and pindels.

[beeemdubbayoo]

You must stick with the 14 LB injectors on the M10 318i - the ECU is non-adaptive. Also, A bad ECU will cause a full rich condition. Also, keep in mind that the coolant temperature sensor on the 1984 1.8 M10 must be working properly or the car might not start at all. The L-Jet is difficult to get running perfect. I would suggest keeping it fully stock until you get it running and idling before trying to tune it for performance.