I have a '91 240 that ran fine one day, and wouldn't start the next. It turns over fine, and it has spark, but isn't getting gas. I might add that the car is an hour away from home, and I'd much rather diagnose and fix it than have it towed to a dealer. Here's what I've done so far in my attempt to diagnose it.

The fuel pumps won't operate. I checked them by jumping fuses 4 and 6 and they both worked, and the car ran although at high idle.

I next checked the relay. Actually, I swapped relays with my other '91
240 and determined that the relay was not the problem; however, there is no
juice at terminal 87/2.

I next checked the diagnostic box for error codes (with the plug in
socket no. 2). I recieved no signal - just steady light. I swapped the
diagnostic box from my other car and the same thing happened. I performed the diagnostics for the ignition and it had an error code stating that the load signal is missing from the ECU.

Next, I tested all of the inputs to the ECU. A few appear to be faulty -
the upshift light ground wire, the AC switch, and the oxygen sensor - but these
shouldn't result in a no-run condition. The grounds appear to be okay, too. I
unplugged the air mass meter to determine if it was the culprit, but no luck.

My Bentley manual refers to an in-line fuse, but my '91 doesn't appear to
have this, or I'm not recognizing it.

I'm running out of ideas, other than the ECU itself may be faulty. I hoped
to swap ECU's between my two '91 240's, but, alas, one has an LH-2.4 and the faulty one is an LH-3.1. As luck would have it, the price for a used or rebuilt
LH-3.1 is much higher than the more common LH-2.4, so I'm trying to diagnose this correctly before ordering a new or rebuilt ECU.

If anyone has any other ideas I'd appreciate hearing them. Also, if anyone
knows of a good source for ECU's please let me know.

Please copy replies to my email: dragnfly@bitstream.net

Thanks!

Tom MacDonald
Minneapolis, MN

>I next checked the diagnostic box for error codes (with the plug in
socket no. 2). I recieved no signal - just steady light.

This is disturbing. When the ECU in my '89 went bad, this is one of the things that happened - no diagnostics. My car would idle, but it would sputter and almost die above 2000 RPM. Final diagnosis was made by swapping ECU's with my '90 - the symptoms followed the ECU.

I wouldn't try swapping LH2.4 and LH3.1 ECUs. There are enough diffrences that I would worry about damage.

Regarding the upshift light ground wire, if your car is an automatic, I don't think it's connected to the ECU. Check the wiring diagram.

>My Bentley manual refers to an in-line fuse, but my '91 doesn't appear to
have this, or I'm not recognizing it.

The in-line fuse under the hood disappeared in '91. My brother and I went crazy looking for it in his '91, before consulting the wiring diagram and determined it wasn't there. The function it provided was moved to one of the fuses in the main fuel panel.

Good luck!

agree with rlangis post below. I too own a 91 240. if the car runs when you jumper the fuel pump fuse(even if at high idle) that tells you the fuse is blown OR, there is so much corrosion, it is grounding out. Pull the fuse. clean the corrosion, put in a known good fuse of proper amperage. Drive the car home. How high is high idle, 1000 rpm, should pose no problem.

my 91 recently began leaking due to rust under the windshield rubber gasket at both lower corners. On the passenger side, the water runs down to the ECU. On the driver side, it runs down to the fuse box; common on 240s. Mine is not bad yet, but suspect i will have problems if i don't fix the source soon.

after you tend to the simple stuff, then rediagnose/reassess.

good luck

Let me clarify what I meant by jumping the fuses - I didn't jump the no. 4 and no. 6 fuses separately - rather, I connected the right terminals of the no. 4 and no. 6 fuses. The no. 6 fuse has power, the no. 4 fuse does not. I think that by connecting them in this manner I'm bypassing the relay and ECU. I can also get the fuel pumps to run by grounding terminals 20 and 21 in the ECU.

One of my '91's is also getting a bit of rust at the right lower windshield corner. I think they're expecially vulnerable if they've had a less-than-perfect windshield replacement in the past. I cleaned mine up as well as I could and had a new windshield/gasket installed.

Thanks for your help,

Tom

Does the car start and run with the fuses jumpered? That's what it reads to me - I'd clean the fuses and connectors of corrosion.

It is possible and "loss of fuel pump ground" is a failure mode. The LH 2.4 uses the 561 or better, the 951 ECU. What does the 3.1 Bosch number end with? What about the bellhousing impulse sender or the in-car fuse. Is the fuel injection wire at the battery terminal tight? Fuel pump ground? I would try to unplug the AMM to try starting too.

Thanks for your reply.

The number on my ECU ends with 572. I have no idea how this ECU differs from the LH-2.4, but I don't want to try swapping them. I looked for the fuse near the battery, but couldn't locate it or didn't recognize it (I'm wondering if the '91 has one?). I will check the connection at the battery and the fuel pump ground (but would I have been able to hotwire the fuel pumps if the ground was bad?).

I did unplug the AMM with no change. Also, I think the sensor that ends in the bellhousing checked out okay (I don't have my notes with me).

Tom