Hey folks. Saturday evening the car abruptly went into limp home mode. I got the green LED in the footwell, indicating that it's the 2,3,5,& 8 bank of cylinders that is shutting down. Towed the car home, and went through several items. Cleaned and gapped plugs,replaced left coil, replaced left coil wire, replaced rotor button, replaced distributor cap, cleaned BOTH temp sensors. (#4 and #8) Still no luck. When the car is cold it seems to run fine, but as soon as it gets up to operating temp, it kicks into limp home mode. What say you, o' knowledgeable list masters??????????????? TIA,

 

For something to do while the Masters are otherwise occupied, swap the ignition module connectors around ( 2x6" black plastic housing, left/drivers side ahead of the rad) - and see if this brings on the red light. If so, .....
BTW, I forget the red/green thing off hand - so, did you also check the other coil & wire?

 

Hi Chris,

Most likely one of the Ignition Monitoring temp probes is dirty or bad. Sometimes removing and reinstalling the probes will clear up your problems for a while. You can also temporarily bypass that system with a Bypass relay, part #928.615.175.00. We have them on the website for $15.23 and I recommend every 89 and later owner to have one in their glovebox for when that system starts acting up. In a pinch you can also remove the relay (large clear relay on engine computer console) and jumper pins 2,4,5 together on the relay socket (leave relay out) which should put you back in to 8 cylinder mode.

 

Twice on the way to work last week, my 89 went into 4 cylinder mode in exactly the same location after hitting a pothole (mental note: use another lane). Pulled over, stopped, restarted and it was fine from then on. Bizarre. At least it didn't stick, so I think it was a transient electrical fault. Only one other time in the 5 years I've owned the car has it gone off. That time I was just toodling along through the Sierras on the way home from an open road race. Stopped and it was OK on restart. If I cannot find a fault, I am I am going to jump it temporarily before the next road race.

 

Chris,

Refresh us on your exhaust modifications and catalytic converter, as the limp home mode is to prevent the "cat on fire" from running too rich.

 

When mine went into 4cyl mode, I switched the coils, coil wires, EGT sensors and final ignition stages one at a time side to side to get the light to change colors/sides. I was hoping to isolate the fault, but could not figure it out. It turned out a plug behind the ezk was loose, and a large bump had sent me into limp home mode. Easy fix after much hair pulling, component switching, and ground cleaning.

Good luck,

Jim R.

 

Jim: What plug behind the EZK was that?

 

Wow, I'm still having this problem as well. Car will run fine for 30-40 miles or a half hour, whichever comes first then limp. Will restart on 8 and run fine for another while. Gonna have to get in there and start cleaning grounds and whatnot but that bypass wire is a good idea to have. Will order tomorrow.

 

Greetings Dave,

So where and how much is an ignition monitoring temp probe (should this symptom ever pop up in my GT)?

 

Bill,

The plug was to the relay if I recall correctly. Connected, but barely, and a big bump was able to break contact on several pins. Pushed it back on and all has been well for many months.

Jim R.

 

Hi Angel,

>So where and how much is an ignition monitoring temp probe (should this symptom ever pop up in my GT)?


Part # 928.606.155.02, current price is $222.44 each. On 89-90 they were mounted at cylinder head exhaust ports 4 and 8, 91-95 at ports 3 and 7. It is recommended that the new updated probes be mounted in the later positions.

 

How might one accomplish this?

 

>How might one accomplish this?

By removing the plugs from 3 and 7 and installing the probes in that location, and installing the plugs from 3 and 7 into 4 and 8. FYI, all cylinders have the ports, the ones not occupied by the probes have plugs (part #900.124.008.02)

 

Ah HAH! Thanks D.R.

 

HMM. Could someone use this to their advantage with some sort of per-cylinder-monitoring setup (if you're highly modded) ?

At what year did these ports become present?