Hello all.
My dad recently picked up a 1964 Mercury Comet, with 5.0 HO and AOD out of an 89-91 Mustang GT swapped in place of the original 289 and C4.
We are having some issues with lean backfiring on slight accelerator application on occasion which I am trying to work through. When the car is able to backfire, it tends to idle roughly. Other times, it idles very smoothly and won’t backfire no matter what is done to the accelerator.
Right off the bat, I have replaced plugs, plug wires, distributor cap and rotor. The issue was happening before and after the swap. The coil has not been changed and still appears to be OEM 5.0 HO.
I checked for vacuum leaks by spraying some carb cleaner around the intake and vacuum lines. I found no signs of any leaks.
I checked fuel pressure at the rail, got ~ 33psi at idle and ~40psi at idle with the FPR vacuum disconnected and plugged.
The car does not have a smog pump, charcoal canister, or a functioning EGR. Those did not make it over in the swap. The EGR valve is in place with no vacuum plumbed, it is just acting as a poor man’s block off plate at the moment.
I have been posting at corral.net, the thread is here. http://forums.corral.net/forums/gen...0-ho-o2-sensor-wiring-check.html#post18059513
My research has shown this site to be a wealth of knowledge, so I figured I see if anyone here has any help to offer. Quickish explanation of what I have done up to now below.
I ran codes on the car, KOEO and KOER. Initially, I got the following...
KOEO:
85 O: Charcoal Canister. This makes sense, since that system did not make it over in the swap. I am planning on living with this code, since it shouldn't affect anything else from what I have seen.
22 CM: Barometric pressure sensor. I replaced the BAP sensor, in doing so I found that the BAP sensor that came in the car was hooked to manifold pressure. I did not hook the new sensor to the manifold. Code 22 has been gone since.
33 CM: EGR. This also makes sense, since the vacuum is not attached to the EGR system. I don't think the whole thing made it over in the swap. I plan to remove the EGR valve and block it off, kit from LMR is on order. I wouldn't mind having EGR if it had been completely swapped over, but at this point it is easier to just completely delete it.
41 CM: I believe this means right hand O2 constantly lean, not switching. More to come on this
KOER:
33: EGR, see above
42: I believe this means right hand O2 constantly rich. Seemingly conflicting with the continous memory code 41.
Seeing what appeared to be a right hand O2 issue, I ordered a replacement O2 sensor (bosch). When I went to install the sensor, I had an issue. The car had NTK sensors, left and right. When drilling the hole in the exhaust pipe on the right hand side, they drilled it JUST big enough for the NTK sensor to fit. The bosch's probe into the exhaust stream is just a tiny bit bigger in diameter, and wouldn't fit. The threaded section is identical, just the physical probes are slighly different in size.
So, I moved the seemingly working left hand sensor to the right hand side, and installed the new bosch sensor on the left hand side, where it fit with no issue. Eventually I will get matching brand O2 sensors in place, but that is not my priority at the moment.
With O2 sensors swapped around, I cleared the codes and tried them out. I still get backfiring out the intake, and codes 41 CM and 42 R. I am still getting 85 CM and 33 CM/R, assume these to be constant going forward.
I verified O2 wiring has continuity from sensor to ECU and ground. I have not yet verified 12V for the heater.
I then used a Fluke 77 DMM and paperclip to jump into pins 43 (left hand) and 29 (right hand) to monitor O2 output. The left hand side appeared to function normally when warmed up, jumping from rich to lean and back every couple seconds. The right hand side was running constantly rich, I thought the signal may have been bad. During this testing, the car was running smoothly and there was no backfiring. I still got codes 41 CM and 42 R
The next day, I tried unplugging the right hand O2 from the harness, and jumping pins 43 and 29 at the ECU. This should have made the compute read the signal from the left hand O2 on both the left and right hand sides. Battery was disconnected for 20 minutes to clear codes. Interestingly, I STILL got codes 41 CM and 42R. No left hand O2 codes, only right hand, even though both sides were getting the same signal.
I hooked everything back up to stock, and have been continuing to monitor pin 29 with a DMM on every drive. I have found that once the O2 starts registering, it tends to read VERY lean for 2-4 minutes, and then in 1-2 seconds jumps up to rich. When the engine is running very lean, it idles poorly and is prone to backfiring. Once the mixture fattens up, it idles MUCH more smoothly and will not backfire.
I took the car for a ride tonight, with my DMM attached to right hand O2 (pin 29) and a fuel pressure gauge sitting next to it. Right off the bat, I will say that the fuel pressure is reading high. I think that is because I had to increase the hose run to ~6 feet to get the gauge safely into the passenger compartment. When I had the gauge hooked up at the fuel rail with the stock length hose, it read 33ish PSI at idle and 40ish at idle with FPR vacuum disconnected. Either way, I was mostly watching for changes in fuel pressure.
View: https://youtu.be/cjERSNT235I
With both gauges hooked up, I went out for a 12 minute ride, videoing the gauges the entire time. The video starts right after initial startup.
It took about a minute and a half for the O2 sensor to start registering. A back fire can be heard a 1:08, and a few more can be heard later on. For the first 7ish minutes, it can be seen that the O2 sensor is registering a very lean condition. During this time, the car idled roughly.
If you are going watch any of the video, I suggest from minute 7 to minute 8. at about 7:15, you will hear some backfiring under very light acceleration. The fuel pressure seems to stay pretty constant, within 1-2 psi during the back fire, and the O2 sensor shows very lean. The fuel pressure does jump a little bit during the back fire, but it appears to actually slightly increase. At 7:30, the O2 sensor shows the mixture pretty quickly goes rich, and idle quality improved. Fuel pressure remained constant during this transition. After the mixture fattened up, there was no more back firing.
Any help or suggestions would be appreciated. I am currently thinking that the fuel trims may be very lean when the ECU is operating in open loop, and it goes rich when it switches to closed loop. I am also leaning towards the ECU potentially being faulty, since it registered 41 CM and 42R but no left hand O2 codes when the left hand O2 signal was fed to both ECU pins. There also could be a leaky EGR affecting things. Once LMR gets the EGR eliminator shipped, I can rule that out.
My dad recently picked up a 1964 Mercury Comet, with 5.0 HO and AOD out of an 89-91 Mustang GT swapped in place of the original 289 and C4.
We are having some issues with lean backfiring on slight accelerator application on occasion which I am trying to work through. When the car is able to backfire, it tends to idle roughly. Other times, it idles very smoothly and won’t backfire no matter what is done to the accelerator.
Right off the bat, I have replaced plugs, plug wires, distributor cap and rotor. The issue was happening before and after the swap. The coil has not been changed and still appears to be OEM 5.0 HO.
I checked for vacuum leaks by spraying some carb cleaner around the intake and vacuum lines. I found no signs of any leaks.
I checked fuel pressure at the rail, got ~ 33psi at idle and ~40psi at idle with the FPR vacuum disconnected and plugged.
The car does not have a smog pump, charcoal canister, or a functioning EGR. Those did not make it over in the swap. The EGR valve is in place with no vacuum plumbed, it is just acting as a poor man’s block off plate at the moment.
I have been posting at corral.net, the thread is here. http://forums.corral.net/forums/gen...0-ho-o2-sensor-wiring-check.html#post18059513
My research has shown this site to be a wealth of knowledge, so I figured I see if anyone here has any help to offer. Quickish explanation of what I have done up to now below.
I ran codes on the car, KOEO and KOER. Initially, I got the following...
KOEO:
85 O: Charcoal Canister. This makes sense, since that system did not make it over in the swap. I am planning on living with this code, since it shouldn't affect anything else from what I have seen.
22 CM: Barometric pressure sensor. I replaced the BAP sensor, in doing so I found that the BAP sensor that came in the car was hooked to manifold pressure. I did not hook the new sensor to the manifold. Code 22 has been gone since.
33 CM: EGR. This also makes sense, since the vacuum is not attached to the EGR system. I don't think the whole thing made it over in the swap. I plan to remove the EGR valve and block it off, kit from LMR is on order. I wouldn't mind having EGR if it had been completely swapped over, but at this point it is easier to just completely delete it.
41 CM: I believe this means right hand O2 constantly lean, not switching. More to come on this
KOER:
33: EGR, see above
42: I believe this means right hand O2 constantly rich. Seemingly conflicting with the continous memory code 41.
Seeing what appeared to be a right hand O2 issue, I ordered a replacement O2 sensor (bosch). When I went to install the sensor, I had an issue. The car had NTK sensors, left and right. When drilling the hole in the exhaust pipe on the right hand side, they drilled it JUST big enough for the NTK sensor to fit. The bosch's probe into the exhaust stream is just a tiny bit bigger in diameter, and wouldn't fit. The threaded section is identical, just the physical probes are slighly different in size.
So, I moved the seemingly working left hand sensor to the right hand side, and installed the new bosch sensor on the left hand side, where it fit with no issue. Eventually I will get matching brand O2 sensors in place, but that is not my priority at the moment.
With O2 sensors swapped around, I cleared the codes and tried them out. I still get backfiring out the intake, and codes 41 CM and 42 R. I am still getting 85 CM and 33 CM/R, assume these to be constant going forward.
I verified O2 wiring has continuity from sensor to ECU and ground. I have not yet verified 12V for the heater.
I then used a Fluke 77 DMM and paperclip to jump into pins 43 (left hand) and 29 (right hand) to monitor O2 output. The left hand side appeared to function normally when warmed up, jumping from rich to lean and back every couple seconds. The right hand side was running constantly rich, I thought the signal may have been bad. During this testing, the car was running smoothly and there was no backfiring. I still got codes 41 CM and 42 R
The next day, I tried unplugging the right hand O2 from the harness, and jumping pins 43 and 29 at the ECU. This should have made the compute read the signal from the left hand O2 on both the left and right hand sides. Battery was disconnected for 20 minutes to clear codes. Interestingly, I STILL got codes 41 CM and 42R. No left hand O2 codes, only right hand, even though both sides were getting the same signal.
I hooked everything back up to stock, and have been continuing to monitor pin 29 with a DMM on every drive. I have found that once the O2 starts registering, it tends to read VERY lean for 2-4 minutes, and then in 1-2 seconds jumps up to rich. When the engine is running very lean, it idles poorly and is prone to backfiring. Once the mixture fattens up, it idles MUCH more smoothly and will not backfire.
I took the car for a ride tonight, with my DMM attached to right hand O2 (pin 29) and a fuel pressure gauge sitting next to it. Right off the bat, I will say that the fuel pressure is reading high. I think that is because I had to increase the hose run to ~6 feet to get the gauge safely into the passenger compartment. When I had the gauge hooked up at the fuel rail with the stock length hose, it read 33ish PSI at idle and 40ish at idle with FPR vacuum disconnected. Either way, I was mostly watching for changes in fuel pressure.
View: https://youtu.be/cjERSNT235I
With both gauges hooked up, I went out for a 12 minute ride, videoing the gauges the entire time. The video starts right after initial startup.
It took about a minute and a half for the O2 sensor to start registering. A back fire can be heard a 1:08, and a few more can be heard later on. For the first 7ish minutes, it can be seen that the O2 sensor is registering a very lean condition. During this time, the car idled roughly.
If you are going watch any of the video, I suggest from minute 7 to minute 8. at about 7:15, you will hear some backfiring under very light acceleration. The fuel pressure seems to stay pretty constant, within 1-2 psi during the back fire, and the O2 sensor shows very lean. The fuel pressure does jump a little bit during the back fire, but it appears to actually slightly increase. At 7:30, the O2 sensor shows the mixture pretty quickly goes rich, and idle quality improved. Fuel pressure remained constant during this transition. After the mixture fattened up, there was no more back firing.
Any help or suggestions would be appreciated. I am currently thinking that the fuel trims may be very lean when the ECU is operating in open loop, and it goes rich when it switches to closed loop. I am also leaning towards the ECU potentially being faulty, since it registered 41 CM and 42R but no left hand O2 codes when the left hand O2 signal was fed to both ECU pins. There also could be a leaky EGR affecting things. Once LMR gets the EGR eliminator shipped, I can rule that out.