Limp mode trouble shooting
09-17-2015, 06:52 AM
#1
Limp mode trouble shooting
I've read a lot of limp mode threads, but most of them seem like they aren't really limp mode or they have CELs that need to be fixed.
I have a '89 Civic, converted OBD1, and ran fine for 6 months or so. The ECU died one day; this was concluded after trouble shooting everything imaginable and then coming back and replacing parts.
The car currently starts and runs with a solid CEL. Jumping the service connector produces no change in CEL status. The car idles high and will not rev past 4,000 RPM according to the stock tachometer.
Without any codes from the check engine light, I'm not sure where to start. I'm looking for any experience with 'limp mode' and where to start.
I have a '89 Civic, converted OBD1, and ran fine for 6 months or so. The ECU died one day; this was concluded after trouble shooting everything imaginable and then coming back and replacing parts.
The car currently starts and runs with a solid CEL. Jumping the service connector produces no change in CEL status. The car idles high and will not rev past 4,000 RPM according to the stock tachometer.
Without any codes from the check engine light, I'm not sure where to start. I'm looking for any experience with 'limp mode' and where to start.
09-20-2015, 12:37 AM
#2
Honda-Tech Member
Re: Limp mode trouble shooting
You can start by providing a detailed vehicle history. When did the problem start? What was the last thing done to the car prior to this problem ocurring? What caused the PCM to fail? What engine/transmission are you using? Are you using an adapter harness? Are you using a Honda PCM? If so, which one? Have you modified interior wiring (specifically, he instrument panel wiring) in any way? Aftermarket gauge covers? etc.
I would start by referencing a schematic for the instrument panel, and determine the sources of power/ground to the CEL itself. Determine if the wires going to it, or from it are spliced, this can indicate another add-on is contributing to the CEL always being lit. You will need to use an isolation method (removing sources of power and ground) to find out what branch of the circuit is illuminating it. Also tell us if the CEL every turns off, and when exactly it turns on.
I would start by referencing a schematic for the instrument panel, and determine the sources of power/ground to the CEL itself. Determine if the wires going to it, or from it are spliced, this can indicate another add-on is contributing to the CEL always being lit. You will need to use an isolation method (removing sources of power and ground) to find out what branch of the circuit is illuminating it. Also tell us if the CEL every turns off, and when exactly it turns on.
09-21-2015, 09:01 AM
#3
Re: Limp mode trouble shooting
I purchased the car (1989 Honda Civic STD) in 2010 with a completely factory motor and transmission. It was a D15B2 (iirc) with a 4 speed transmission and stock OBD0 ECU.
2014: I swapped the motor to a JDM B16A with YS1 transmission, converting the car to OBD1 to run a P28 ECU with a Neptune Demonboard v1.2. The car has an adapter harness in the cabin and I soldered new connectors in for the plugs in the engine bay.
The dashboard is stock as far as the wiring is concerned. The gauge cluster has been swapped with a SI cluster for the addition of the tachometer. The wires for the CEL are factory and have never been touched.
Between 6 and 8 months passed since finishing the swap. I was driving the car on a regular basis with no issues after my initial swap issues (map sensor missing Vac line, VTEC solenoid needed to be cleaned, FITV/IACV cleaning, etc). I changed the head gasket and installed ARP head studs in preparation to turbo the car. This was the only mod to the motor.
I parked the car one evening, packed it up in preparation to move out and into our new home, and it wouldn't start. There was a solid check engine light that would not blink when the service connector was jumped. I have, in the past, checked the CEL with success. The car would turn over, get spark, but not start. There was a fueling issue. The cause of this is completely unknown.
I towed the car to my new home. It sat on jack stands while we moved in and got settled in our new home. I did some trouble shooting for the fuel pump, decided to replace it with the Walbro unit I purchased. It was a known good unit. I followed the factory service manual for troubleshooting the ignition switch, found no issues. I also checked my three major grounds, something I preach regularly. I found no issues with the valve cover, transmission, or thermostat housing grounds.
The check engine light turns off when you turn the car off. It comes on when the key is placed in the ignition but doesn't turn off after a few moments, which it should do from my experience. After replacing the ECU, I was able to start the car. The check engine light stays illuminated and will not blink with the service connector jumped. I cannot check the codes with my Neptune software either.
The car idles a little wonky, a bit higher than it normally does. It will also start to surge after the car warms up, something I attest to the fact that it has been sitting for a year (FITV). The car will drive but not rev past 4,000 RPM according to the factory tach. I presumed this to be limp mode.
I was hoping to receive advice on the most common causes for limp mode. Hopefully they would be things I have not tested.
2014: I swapped the motor to a JDM B16A with YS1 transmission, converting the car to OBD1 to run a P28 ECU with a Neptune Demonboard v1.2. The car has an adapter harness in the cabin and I soldered new connectors in for the plugs in the engine bay.
The dashboard is stock as far as the wiring is concerned. The gauge cluster has been swapped with a SI cluster for the addition of the tachometer. The wires for the CEL are factory and have never been touched.
Between 6 and 8 months passed since finishing the swap. I was driving the car on a regular basis with no issues after my initial swap issues (map sensor missing Vac line, VTEC solenoid needed to be cleaned, FITV/IACV cleaning, etc). I changed the head gasket and installed ARP head studs in preparation to turbo the car. This was the only mod to the motor.
I parked the car one evening, packed it up in preparation to move out and into our new home, and it wouldn't start. There was a solid check engine light that would not blink when the service connector was jumped. I have, in the past, checked the CEL with success. The car would turn over, get spark, but not start. There was a fueling issue. The cause of this is completely unknown.
I towed the car to my new home. It sat on jack stands while we moved in and got settled in our new home. I did some trouble shooting for the fuel pump, decided to replace it with the Walbro unit I purchased. It was a known good unit. I followed the factory service manual for troubleshooting the ignition switch, found no issues. I also checked my three major grounds, something I preach regularly. I found no issues with the valve cover, transmission, or thermostat housing grounds.
The check engine light turns off when you turn the car off. It comes on when the key is placed in the ignition but doesn't turn off after a few moments, which it should do from my experience. After replacing the ECU, I was able to start the car. The check engine light stays illuminated and will not blink with the service connector jumped. I cannot check the codes with my Neptune software either.
The car idles a little wonky, a bit higher than it normally does. It will also start to surge after the car warms up, something I attest to the fact that it has been sitting for a year (FITV). The car will drive but not rev past 4,000 RPM according to the factory tach. I presumed this to be limp mode.
I was hoping to receive advice on the most common causes for limp mode. Hopefully they would be things I have not tested.
Thread
Thread Starter
Forum
Replies
Last Post
steveteggy92
Acura Integra
9
06-21-2011 11:49 AM
slowcrxsib16
Honda CRX / EF Civic (1988 - 1991)
7
01-17-2007 03:41 AM