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I have a '97 motorhome with the 7.5 efi with no cat spec. It seems to run and idle very well. Smog test failed due to high co at idle (passed in all other areas). I am hoping somebody out there could help me prioritize things to check based on your experience. Before I took it for the smog test I had an exhaust leak out of the right side manifold. I replaced the gasket. It's quieter but still has an exhaust leak, it's not real bad but you can tell there is a leak, the o2 sensor is downstream on that same side. Do you think the leak would fool the o2 sensor to believe lean and increase duty cycle or whatever it does causing rich at idle?. I would appreciate your advice
 

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Are there any codes? CEL?
 
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I don't have a reader for this EECIV system and i've been fumbling around trying to come up with jumpers and pins so I can answer that question but that is not working out cuz my setup so far keeps falling apart!. I'm going to get some 1/8" wide male terminals in the morning and make some wires instead of trying to hold everything together. I can say the check engine light operates correctly at ign on, then goes out after startup. I'll be back on here tomorrow Thanks
Are there any codes? CEL?
 

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Your 460 did not have exhaust manifold gaskets from the factory. If you want to cure the leak, remove the manifold and have it surfaced. Then take a flat wet stone and some mineral spirits and clean the ports on the head. Then reinstall with no gasket. The O2 sensor looks like it reads all 8 cylinders but it only reads the left bank. Look closely. Make sure there are no vacuum leaks in the hose going to the MAP sensor. Located next to the EEC-IV port.

Richard
 

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Your 460 did not have exhaust manifold gaskets from the factory. If you want to cure the leak, remove the manifold and have it surfaced. Then take a flat wet stone and some mineral spirits and clean the ports on the head. Then reinstall with no gasket. The O2 sensor looks like it reads all 8 cylinders but it only reads the left bank. Look closely. Make sure there are no vacuum leaks in the hose going to the MAP sensor. Located next to the EEC-IV port.

Richard
Will do on the exhaust manifold, thank you. The o2 sensor is on the rh bank about 8 or so inches downstream from the manifold on this Coachmen motor home it is the same side as the manifold leak. As far as the map sensor. The hoses fit too loose on the sensor and the throttle body. I'll be replacing those as the hoses keep wanting to fall off of both ends. Appreciate the help
 

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I don't have a reader for this EECIV system and i've been fumbling around trying to come up with jumpers and pins so I can answer that question but that is not working out cuz my setup so far keeps falling apart!. I'm going to get some 1/8" wide male terminals in the morning and make some wires instead of trying to hold everything together. I can say the check engine light operates correctly at ign on, then goes out after startup. I'll be back on here tomorrow Thanks

OK here's what I got this morning for codes
KOEO 111
CMC 128 MAP vacuum has not been changing – check vacuum lines – “>MAP
Your 460 did not have exhaust manifold gaskets from the factory. If you want to cure the leak, remove the manifold and have it surfaced. Then take a flat wet stone and some mineral spirits and clean the ports on the head. Then reinstall with no gasket. The O2 sensor looks like it reads all 8 cylinders but it only reads the left bank. Look closely. Make sure there are no vacuum leaks in the hose going to the MAP sensor. Located next to the EEC-IV port.

Richard
The o2 sensor is on the left like you said. I had a different vision of it in my head I guess

Codes from this morning
KOEO 111
CMC 128 MAP vacuum has not been changing – check vacuum lines – “>MAP
Has good hoses and lots of vacuum so I've ordered a new MAP sensor I will pick up this afternoon, so my question is do you think the bad map sensor would cause enough trouble to raise the co at idle or do you think that could be the problem thanks again
 

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OK here's what I got this morning for codes
KOEO 111
CMC 128 MAP vacuum has not been changing – check vacuum lines – “>MAP

The o2 sensor is on the left like you said. I had a different vision of it in my head I guess

Codes from this morning
KOEO 111
CMC 128 MAP vacuum has not been changing – check vacuum lines – “>MAP
Has good hoses and lots of vacuum so I've ordered a new MAP sensor I will pick up this afternoon, so my question is do you think the bad map sensor would cause enough trouble to raise the co at idle or do you think that could be the problem thanks again

High CO is typically caused by a rich condition so a properly functioning map and elimination of the exhaust leaks should address the issue.

SJ
used 2b RHP


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If the MAP sensor is old and failing, it has been my observations that it will make the mixture richer. That is only a SWAG.

Richard
 

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I think when you retest with the new map and hoses it'll pass. A bad map and/or unreliable vacuum supply to it can absolutely screw up the air/fuel ratio.
 

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I have a '97 motorhome with the 7.5 efi with no cat spec. It seems to run and idle very well. Smog test failed due to high co at idle (passed in all other areas). I am hoping somebody out there could help me prioritize things to check based on your experience. Before I took it for the smog test I had an exhaust leak out of the right side manifold. I replaced the gasket. It's quieter but still has an exhaust leak, it's not real bad but you can tell there is a leak, the o2 sensor is downstream on that same side. Do you think the leak would fool the o2 sensor to believe lean and increase duty cycle or whatever it does causing rich at idle?. I would appreciate your advice
This engine has an unusual PCM calibration, probably as it has no catalytic converter. The engine pretty much never runs in closed loop fuel control, and as a result, the PCM never gathers any fuel corrections. So you don't need to worry about the O2 sensor affecting anything. Which can be unfortunate because if you have to run E10 gasoline, the PCM will be unable to correct the 5% leaner mixture that this provides.

Anyway, that isn't your problem. Which state's emissions test are you having to pass, and can you post the results of your test.

The 111 code means the test sequence finished. The MAP sensor code means that that the engine isn't able to measure how much air is going into the engine. The MAP sensor is the primary method, without that working, it reverts to using the throttle position sensor.

I wouldn't run out and get a new map sensor until you check the condition of the hose that connects it to the intake manifold. The intake connector is at the rear of the 90 degree elbow that the throttle body mounts on, at the back of the engine just above the bellhousing. Locate that, and follow it arount the rear of the engine cover opening to the driver's side, and then forward to the front edge of the cover. The MAP sensor is a black plastic box mounted a little forward of that and a little higher up.

The hose may have come off, or it may be split. The output of the Ford MAP sensor is a frequency, so you won't learn anything with a voltmeter.

You could also see if your thermactor air pump is still working. It's air may be required in order to pass emissions, but just a pump failure shouldn't give you too high a CO level.
 

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I might be comparing an apple to an orange but my 87 motorhome..carb with no computer controls had the same problem..Would pass the high RPM test but failed at the idle..I had a weak cylinder from a bad valve and it had compression of about 85 when the rest of the cylinders were 120ish..So at idle it was just pumping raw gas and CO and could not even come close to passing..
Do a compression test..
 

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If the engine is never in closed loop, why have an 02 sensor? Or does it run in closed loop but only occasionally?
 

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If the engine is never in closed loop, why have an 02 sensor? Or does it run in closed loop but only occasionally?
Having worked at big companies although not Ford, sometimes these things are hard to understand. I'd guess that the number of RVs made back then didn't make it worth doing the calibration properly, and most of it's life would be spent under so much load that it be outside the parameters for closed loop anyway. SO if you delete the O2 sensor, then you need a new PCM calibration. It's possible it would run in closed loop while under very low load at low rpm, but not at closed throttle. Carrying that much weight (no cats only allowed at over 14,500# GVWR) and with those aerodynamics would probably mean you'd only be in closed loop going down hill. Idles in open loop also.
 

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Discussion Starter #14
Thank You all for sharing your knowledge. After replacing the MAP sensor and getting rid of an exhaust leak on the manifold she passed with flying colors and I have my California smog certificate and can get this thing registered. I gained some knowledge on this engine from all y'all thanks again
 
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