348 dropping 58 someone please help

My 91 348 is intermitantly dropping bank 5/8. I've swapped all sensors to the 1/4 side, cleaned all connectors but the problem still exists. I think the next step would be to attack the wiring harness leading to the crank sensor. Is there an easier way to track it down without removing the motor to expose the harness? Can anyone tell me how to get hold of a wiring diagram to try and track this problem. Any and all info will be greatly appreaciated.

If the "slow down 5-8" light is being illuminated you may be suffering from an exhaust computer failure or the thermocouples after the cat have gone south.

Theusual test is to move the exhaust ECU from the offending 5/8 side over to the 1/4 side. Once done, you look to see if the SLOW DOWN light switches from 5/8 over to 1/4.

If yes, the light switches, then the problem is typcially a failed exhaust ecu.

If no, the light still says SLOW DOWN 5/8, then you probablyhave a real problem such as an overheated cat that could catch fire and burn down your car and kill you and your passenger.

Is your cat on the 5/8 side glowing a dim red after a drive?

Also, check here for more SLOW DOWN info and tests: The348.com .

Actually it's a lot easier to just unplug the Cat ECU's and see if the "slow down" light goes off. However, if the light is coming on & it's not cutting out one bank of cylinders, then the problem lies elsewhere.

The car doesn't have cats and the cat ecu are disconnected.

Well since you are running pipe and the cat ecu's are 86'd then here is what I would check.

1)Pull the ecu codes from both sides.

2)Condition of the spark plugs, and spark plug wires

3)Make sure that the Mass Air Flow Sensors are clean, that the connections are clean, and that the wires are in good condition under the rubber boots.

4)Make sure all your ground wires are connected properly

5)The condition of the wires under the rubber boots behind the connectors for the crank sensors, and make sure they are connected properly

6)The condition of the connections for the fuel rails. Those are located up under the intake plenum. You can see them on either side of the oil filter.

7)When was the last time you changed the fuel filters? If it has been a while you may want to give that a looksy.

Try those for now.

The codes he is getting is for the RPM sensor, plugs and wires have checked out ok, mass air flows are good and switching from side to side does not move the problem, all connections should be clean , they were cleaned in Jan when I owned the car and had the major done, the fuel rails are fine I had them off then and the injectors cleaned then also, the fuel filters were replaced in Jan. The shop is telling Tim that the car is losing electrical power to the 5/8 ECU they advised him to replace the fuse panel but when he removed the panel he did not see any burned spots

He DOES NOT need to replace the fuse pannel.

Have him swap the crank sensors. They can be swapped in the same amount of time it took to swap the cat ecu's. Try that and see what that does. Make sure that the Motronic ecu's behind the seats are properly bolted to the body. The screws help to ground the ecu's. There are two screw for each ecu, with located one on top and one on the bottom. He can also swap the ecu's from side to side and see if that helps with the problem. He could have a bad ground issue with the Motronics that is causing him to get the CELs.

As for checking the wires, I mean the ones that are at the back of the connector, under the rubber boot, on the wiring loom side, not the wire on the sensor. You have to peal the boot back in order to see the wires. If you have a buddy with a running 348 you can borrow his cps's and see if that gets rid of the cel's. All you have to do is get the car up in the air enough so you can slide under it. The wiring loom connectors are right there.

If, and I mean IIIFFFFF, there is a problem with the fuse pannel, he should take it out, and apart, then clean it up. But I SERIOUSLY DOUBT that there is a problem with the fuse pannel. Again IF there is, it could be that there is a blow fuse or a bad relay that is an easy fix. There is NO need to replace the entire fuse pannel. So check out the fuses and relay that are in the kick pannel.

Better yet just take it to another shop. I don't like the sound of what these guys are saying. You don't solve a problem by throwing parts at it. You find THE problem and then fix THE problem.

The Motronic has 2 relays per side. Cheap standard parts, no Ferrari special, don’t have to be Bosch. Replace all 4 of them. You don’t loose to much money if they are not the cause.

I just spoke with Tim and he has changed the crank sensors and swapped the relays the problem is still there.