348 1-4 cylinder bank shut down. Ideas?

**Husker** · #1 05-01-2004, 09:47 PM

My 1990 348 ts has a strange problem. Runs fine part of the time. Just drove it 400 miles home from Dallas with no problems. Drove it this a.m. with no problems. Then, later this afternoon, I started the car and it was hesitant in starting, then when I drove the car after starting it the power was reduced by half. Then, the "check engine 1/4" light came on, went off, and kept coming on and going off. The car never resumed full power. I am guessing that cylinder bank 1/4 is shut down. Any ideas on where to start on this one?

A month ago, the same thing was occuring except this time it was the "Check Engine 5/8" light was on. Same circumstances, same loss of power issue.

When I sent the car to Dallas for another, unrelated repair, the mechanic could not find a stored code in the ECU, nor could he get the "Check Engine" light(s) to come back on. So, here I am at! I'm just glad it didn't happen during my 400 mile trek home!!

Any ideas or suggestions would be greatly appreciated. Also, does anyone know how to interpret the codes, and how to get them? Thanks!

henryk · #2 05-01-2004, 10:23 PM

It is either one of 2 problems: Fuel pump, or coil wire to that bank. Since it appears intermittent, I would check for a loose wire on the coil side, or a loose ground to the fuel pump.

**WILLIAM H** · #3 05-01-2004, 10:28 PM

My 512TR did that once, when I restarted her she ran fine

kenyon · #4 05-02-2004, 12:41 AM

Its the CAT ecu's not - The temperature probes. The CAT are getting to hot and shutting down the cylinder bank. Its nearly 99% of the time a ECU/thermo probe fault.

Disconnect battery fully, postive and negative terminals.
Reconnect,
then start engine,
let engine idle for 10-15 mins with no reving only on tick over.
This resets the ecus.
Switch off engine,
start again and go for a drive, should be OK.

**ernie** · #5 05-02-2004, 01:32 AM

Are you sure it wasn't the SLOW DOWN 1/4 and 5/8, and not the check engine? I'm willing to bet it is. It is one of two things. Either your cats are on the way out and you are getting a true reading, or the exhaust ecu's are on the blink. What the exhuast ecu's do is monitor the temperature of the cat's if the affected cat gets above a certain temperature they give you a warning to slow down. They will show you the bank of cylinders that the cat is getting hot on, 1/4 or 5/8. If the cat's continue to give the ecu a high temperature reading, the exhaust ecu will shut the bank of cyinders down to prevent damage to the cat. So that is what you are experiencing when you had the power loss. It also is audable that you have lost a bank, as the engine note changes. Quite often the exhaust ecu's go bad, but it usually is only one ecu that is giving the false reading. Since you had both come on, it would be worth you while to have the condition of the cat's looked at. You could have one, or both, of the internals of the catalytic converters coming appart, resulting in a blockage of the exhaust flow causing the cat to get hot.

**Husker** · #6 05-02-2004, 08:55 PM

Kenyon, thank you. I will try these items tonight. Ernie, it definitely IS the "check engine 1/4" light, NOT the "slow down" light. Any other thoughts Ernie?

Also, it seems this is no longer "intermittent". The right bank of cylinders are "no go" now every time I start the car. I've driven it around the block a few times and it's just running on the left cylinder bank.

Any more help is very much appreciated. Thaks everyone.

**Miltonian** · #7 05-02-2004, 09:00 PM

There should be something stored in the memory of the Motronic ECU for the 1/4 bank. From your first post, it appears that you do not know how to download and interpret the code - is this correct? It isn't difficult, no special tools needed. It's just a series of blinking lights. Described in detail in the Workshop Manual.

**ernie** · #8 05-02-2004, 09:45 PM

Have a look at the crank position sensors. They are located at the bottom and side of the pully for the alternator, and air conditioning belts. You could have one that is bad, or not connected properly. However if you got a check engine light, the computer should have a code stored. Especially since the car is only running on one bank at start up.

If you want you can just unplug the cat ecu's altogether, and see if that solves the problem. If it is a bad cat ecu, the car can run with them unplugged. You can also try switching the ecu from one side to the other and see if you get the problem on the other side.

**ShanB** · #9 05-02-2004, 10:59 PM

I would start by going over the wiring diagram to see what circuits "check engine 1-4" monitors and work backwards. There are something like four or five things that could make that light go on. (RPM sensor at intake crankshaft cyl 1-4 for example) However for a quick check I would agree with Ernie that the crank position sensor is a typical suspect. FYI - the cylinder 1-4 crank sensor is the one at the six o'clock position in the picture.
Good luck!

airbarton · #10 05-03-2004, 07:50 AM

Ernie's right, crank sensor is most likely the problem. I had the same thing once. Turned out to be a loose connection on the sensor.

**Jack Russell Racing** · #11 05-03-2004, 07:58 AM

There are some better pics from ShanB in this thread:

http://ferrarichat.com/forum/showthr...t=crank+sensor

**Husker** · #12 05-03-2004, 10:11 AM

Quote:

Originally Posted by ernie

Have a look at the crank position sensors. They are located at the bottom and side of the pully for the alternator, and air conditioning belts. You could have one that is bad, or not connected properly. However if you got a check engine light, the computer should have a code stored. Especially since the car is only running on one bank at start up.

If you want you can just unplug the cat ecu's altogether, and see if that solves the problem. If it is a bad cat ecu, the car can run with them unplugged. You can also try switching the ecu from one side to the other and see if you get the problem on the other side.

Ernie, if I were to unplug that "cat ecu's" where are they to unplug? If this fixes the problem, would you keep them unplugged indefinitely? Long term problems associated with this?

**ernie** · #13 05-04-2004, 01:29 AM

I posted in your other thread how to find the exhaust ecu. I ran my car for over six months with the exhaust ecu unplugged. All it does is tell the motronic ecu if the cats are getting hot. I knew mine was bad because after the car sat all night, as soon as I started the car in the morning the light came on. Just to make sure I switched it from one side to the other, and sure enough I had the slow down light on on the other bank now. So I just left it unplugged. I did this because I had brand new cats, and knew they were good. The problem comes when you leave it unplugged and then you really do have a cat that is bad. If the cat gets to hot it will destroy the insides, and your emissions will be screwed. The other bad thing is that the cat wil get cherry red hot and could cause a fire. So just check to make sure you don't have a bad exhaust ecu. But don't forget to check the crank position senors.

jkuk · #14 05-04-2004, 06:05 AM

Quote:

Originally Posted by ernie

I posted in your other thread how to find the exhaust ecu. I ran my car for over six months with the exhaust ecu unplugged. All it does is tell the motronic ecu if the cats are getting hot. I knew mine was bad because after the car sat all night, as soon as I started the car in the morning the light came on. Just to make sure I switched it from one side to the other, and sure enough I had the slow down light on on the other bank now. So I just left it unplugged. I did this because I had brand new cats, and knew they were good. The problem comes when you leave it unplugged and then you really do have a cat that is bad. If the cat gets to hot it will destroy the insides, and your emissions will be screwed. The other bad thing is that the cat wil get cherry red hot and could cause a fire. So just check to make sure you don't have a bad exhaust ecu. But don't forget to check the crank position senors.

I note of warning with the crank sensor connectors.

My 348 would not start - no spark on 5-8 bank. The crank connector was the source, but only when I removed the rubber shroud did I find the true problem.

The centre wire and power wire were both shorting together. The insulation had worn through over time giving a resultant intermittent fault.

So just cleaning them may fix a crank sensor problem, but whenever checking this area I would also check the integrity of the wiring.

John

ants2au · #15 05-07-2004, 12:10 AM

I may have this wrong, but on the 512TR WSM (wich runs Bosch 2.7), the crank sensors (this is from memory now) are used to provide TDC and injector firing pulse.

The ignition firing is handled by another set of sensors on the back of one of the cams.

Someone correct me.

Quote:

Originally Posted by jkuk

I note of warning with the crank sensor connectors.

My 348 would not start - no spark on 5-8 bank. The crank connector was the source, but only when I removed the rubber shroud did I find the true problem.

The centre wire and power wire were both shorting together. The insulation had worn through over time giving a resultant intermittent fault.

So just cleaning them may fix a crank sensor problem, but whenever checking this area I would also check the integrity of the wiring.

John

**Husker** · #16 05-07-2004, 03:11 PM

It was the oxygen sensor gone bad. Anyone know how much $ I should expect to pay for an O2 sensor?

**ernie** · #17 05-07-2004, 03:23 PM

The O2 senors should only be about $100 - $120. You can find them online.

**fatbillybob** · #18 05-11-2004, 06:43 AM

Quote:

Originally Posted by huskerNtexas

It was the oxygen sensor gone bad. Anyone know how much $ I should expect to pay for an O2 sensor?

Actually, this is about the best part in the car. Most of these cars don't even have 50k miles on them and more 02 sensors are replaced than need to be replaced. Cehck the wiring to the sensors. You can also switch left to right and get the car really hot and sometimes burn off all the crap that you now have fouled on the 02 sensor from running on 4 lungs. More often than not the problem is the connection of the 02 sensor to the car wiring.

likeyoudontknow · #19 05-13-2004, 01:32 PM

So what happens to the bank if you delete the cats? Do you still need a 02 sensor?

likeyoudontknow@hotmail.com

**ernie** · #20 05-13-2004, 10:38 PM

Quote:

Originally Posted by likeyoudontknow

So what happens to the bank if you delete the cats? Do you still need a 02 sensor?

Yes you still need the O2 sensors. They measure the amount of unburnt fuel coming out of the engine, before the catalytic converters. If the exhaust is rich, then the ECU will lean out the fuel supply. If the exhaust is too lean, based on the signal coming from the O2 sensors, then the ECU will richen up the fuel supply. What the ECU is trying to accomplish is getting the air fuel ratio of 14/1. That is 14 parts air to one part fuel. If you don't have the O2 senors, there is no way for the ECU to know what the engine is doing, and the engine won't run right. Also this is why the car doesn't wanna run right if one or both of the O2 sensors aren't working. What happens is that the tips get clogged over time with build up, and thus can't read the exhuast gasses properly.