Start/No Start & MAPP Sensor Unplugged

[LBR]

Hi Guys…another newbie with 6.0 problems….my truck is a 2003 F-550 Chassis Cab 4x2 which I purchased in May/2005 with 22K miles on the clock. The previous owner used it for towing a huge 5er.

Besides a six year problem with 1) batteries going dead after 3 days of non-use and in the last two years 2) won’t start nor fire half the time, one day it lost virtually all (95%) engine power. After quite a long process, the local shop found with the MAPP sensor plugged in, it would barely escape it’s own shadow, but with it unplugged, it runs like a John Force Racing F/C, with the only down side being the infamous ‘Check Engine’ light on. A brand new MAPP sensor was put in, but made no difference. After some research, they are getting more confused about why when the MAPP sensor is unplugged, it runs great.

A friend told me that possibly the previous owner had chipped the ECM (Superchip?) and if that tune had been removed before me buying it, some of the performance enhancing files may be creating havoc with the ECM, similar to a computer virus if you may. Are we on the right track with this thinking? So it was suggested to have the ECM completely formatted, then reprogrammed in case some stray aftermart performance data is the culprit. By a friend’s suggestion, I’m thinking of having it done by IH with their tune in the ECM. Thanx in advance.

[LBR]

Originally Posted by LBR

Hi Guys…another newbie with 6.0 problems….my truck is a 2003 F-550 Chassis Cab 4x2 which I purchased in May/2005 with 22K miles on the clock. The previous owner used it for towing a huge 5er.

Besides a six year problem with 1) batteries going dead after 3 days of non-use and in the last two years 2) won’t start nor fire half the time, one day it lost virtually all (95%) engine power. After quite a long process, the local shop found with the MAPP sensor plugged in, it would barely escape it’s own shadow, but with it unplugged, it runs like a John Force Racing F/C, with the only down side being the infamous ‘Check Engine’ light on. A brand new MAPP sensor was put in, but made no difference. After some research, they are getting more confused about why when the MAPP sensor is unplugged, it runs great.

A friend told me that possibly the previous owner had chipped the ECM (Superchip?) and if that tune had been removed before me buying it, some of the performance enhancing files may be creating havoc with the ECM, similar to a computer virus if you may. Are we on the right track with this thinking? So it was suggested to have the ECM completely formatted, then reprogrammed in case some stray aftermart performance data is the culprit. By a friend’s suggestion, I’m thinking of having it done by IH with their tune in the ECM. Thanx in advance.

Well, looks like no one here knows the answer either...Thanx for reading anyway.

[twoicebergs]

Your MAF (not MAP) and EGR valve may be part of the problem. However, without any further info from a monitor or diagnostic tools it is tough to give you any good help over the internet. If you go to the 6.0l coffee table book or the repair manual, you can see the MAP is more of information versus controlling parameters.

• The PCM uses the MAP sensor signal to assist in the calculation of EGR duty cycle.

• The PCM measures the MAP signal to determine intake manifold (boost) pressure.

So, if it is screwing up the EGR duty cycle, that would give you lousy performance. Since you changed the sensor, that would be an indication you may have a wiring problem or your EGR valve may not be working correctly. I would start by cleaning and verifying the correct operation of the EGR valve.

[LBR]

Originally Posted by twoicebergs

Your MAF (not MAP) and EGR valve may be part of the problem. However, without any further info from a monitor or diagnostic tools it is tough to give you any good help over the internet. If you go to the 6.0l coffee table book or the repair manual, you can see the MAP is more of information versus controlling parameters.

• The PCM uses the MAP sensor signal to assist in the calculation of EGR duty cycle.

• The PCM measures the MAP signal to determine intake manifold (boost) pressure.

So, if it is screwing up the EGR duty cycle, that would give you lousy performance. Since you changed the sensor, that would be an indication you may have a wiring problem or your EGR valve may not be working correctly. I would start by cleaning and verifying the correct operation of the EGR valve.

Thank you for the info....

We were told that without the MAP sensor plugged in, performance would be poorer rather than better, such as in my case. Also there would probably have to be a program that would supersede the MAP signal, such as a Superchips in the ECM. With your explanation, it becomes apparent the the MAP is for reading information purposes more so than the controlling a function.

So with it being unplugged, do you think that in itself would allow the turbo to boost up more since the ECM cannot read the MAP sensor for intake pressures? This truck has never run this strong, so could I be over-boosting at WOT and should be concerned? The EGR is on the list to clean...Lance

[twoicebergs]

It doesn't use MAP to control boost, just EGR duty cycle. However, it will use it and a few other parameters to set codes if parameters are exceeded. The boost is a function of EBP and vane position, not the other way around, even if EBP is inferred.

[LBR]

Thank You!