Black dawg
Registered User
I ask, because I have seen it...... Saw a vac line connected to windshield squirters also.....
Computer keeps throwing maf codes
- Thread starter TheMadHatter
- Start date
TheMadHatter
Registered User
I was debating on posting this or waiting until I put more miles on it ( and I was rushing and didn’t take pictures yet) but as of 12 hours ago the code is cleared and has not returned I wired in a gm three wire map sensor and it so far likes it I’ll try to get the part numbers and specs if it continues to work
TheMadHatter
Registered User
Wait what (insert record scratch)
A map sensor without a vacuum will not work
Manifold
Absolute
Pressure
Sensor
Now on a diesel since the vacuum is made by a pump not the vacuum of the crankcase the line must be run from the log to a very small line but a maps sensor needs vacuum or the range will never change unless you are changing altitude.
Now a mass air flow meter doesn’t get a vacuum line since it is connected to the air intake ( but 7.3 idi) doesn’t care about anything outside of if it has enough power to keep the fuel shutdown powered
A map sensor without a vacuum will not work
Manifold
Absolute
Pressure
Sensor
Now on a diesel since the vacuum is made by a pump not the vacuum of the crankcase the line must be run from the log to a very small line but a maps sensor needs vacuum or the range will never change unless you are changing altitude.
Now a mass air flow meter doesn’t get a vacuum line since it is connected to the air intake ( but 7.3 idi) doesn’t care about anything outside of if it has enough power to keep the fuel shutdown powered
TheMadHatter
Registered User
Black dawg the overdrive light with start blinking and it won’t step shift. Think slam shifting a old ford 4 spd and won’t run faster than 45mph
The tps was a issue but a adjustment fixed that
The tps was a issue but a adjustment fixed that
IDIBRONCO
IDIBRONCO
I had that happen on my 1984 Mustang that I used to have. For some reason that a hose had been cut. Since it went inside the driver's side fender, I though that it was a vacuum line. I spliced it back together and stopped at Auto Zone to buy some washer fluid. After I filled the reservoir, I started to drive home and it started running like crap right away. The car was still new to me so I kept driving. Suddenly I noticed that it was smoking BADLY out of the exhaust and I thought that the engine was about to fail. After a couple more minutes, the smoke cleared up and the engine ran just fine again. Later I opened the hood and saw that the washer fluid reservoir was empty again so I put two and two together. I plugged off the engine side of my splice and drove it for 6 more years.
Black dawg
Registered User
So you have a vac line connected to the map sensor?
XOLATEM
Full Access Member
All of the above is good input and I am just an armchair quarterback here since currently, I am not in the trenches as a mechanic on a day-to-day basis....but I remember working on those trucks when they needed transmission work back in the day.
Please, just(!) pull the kick panel on the drivers side and see if you can see any numbers on the TCM to see if @Rdnck84_03 hit the nail on the head with the original computer being swapped for a gas unit..??
On a diesel TCM, you should not even HAVE any MAP or MAF codes.
There is no MAF on the durn thing and any MAP you might have would only be a belt-driven vacuum pump monitor thats only purpose would be to warn you that you don't have any vacuum to power your brakes.
MAP and MAF is for gas engines. It has no business being on a diesel of that vintage.
As far as other sensors...if one of them is ailing...it might pull the others down that are three-wire sensors and use a common source voltage. So....that might cause a code that drags you down a rabbit hole.
This guy guessed that the truck could have been converted from gas to diesel...that is possible.
To find out...look at your VIN and decode the thing...it will tell you if the truck was originally a gas or diesel and then let's start with that and check to see if you have a TCM to match the engine.
Anything else done or time spent on it before you find out what you really have to work with will be chasing your tail.
Back to basics, first.
Also...a GM MAP does not use the same method of signalling the computer that the Ford MAP does...ask me how I know...wait, don't ask...it cost me a better grade on a written test...back in the 1990's...
The Ford uses a Hertz signal, the GM one uses 0-5 VDC.
The diesel BARO sensor is the only thing that your truck would use. You don't connect any vacuum hose to it.
Just(!) trying to help....
Please, just(!) pull the kick panel on the drivers side and see if you can see any numbers on the TCM to see if @Rdnck84_03 hit the nail on the head with the original computer being swapped for a gas unit..??
On a diesel TCM, you should not even HAVE any MAP or MAF codes.
There is no MAF on the durn thing and any MAP you might have would only be a belt-driven vacuum pump monitor thats only purpose would be to warn you that you don't have any vacuum to power your brakes.
MAP and MAF is for gas engines. It has no business being on a diesel of that vintage.
As far as other sensors...if one of them is ailing...it might pull the others down that are three-wire sensors and use a common source voltage. So....that might cause a code that drags you down a rabbit hole.
This guy guessed that the truck could have been converted from gas to diesel...that is possible.
To find out...look at your VIN and decode the thing...it will tell you if the truck was originally a gas or diesel and then let's start with that and check to see if you have a TCM to match the engine.
Anything else done or time spent on it before you find out what you really have to work with will be chasing your tail.
Back to basics, first.
Also...a GM MAP does not use the same method of signalling the computer that the Ford MAP does...ask me how I know...wait, don't ask...it cost me a better grade on a written test...back in the 1990's...
The Ford uses a Hertz signal, the GM one uses 0-5 VDC.
The diesel BARO sensor is the only thing that your truck would use. You don't connect any vacuum hose to it.
Just(!) trying to help....
Last edited:
XOLATEM
Full Access Member
If you had a borescope at that time and looked down the spark plug hole you would have seen that you had cleaned the combustion chamber and the tops of the pistons real nice...
These days, people pay good money for that service. No wonder it ran so well after...
I'd be curious to see what the catalytic convertor looked like on the entry side...though...
Good story. I'd like to hear more...
IDIBRONCO
IDIBRONCO
I know it would have. My dad taught me about pouring Rislone down the carb. My first Dent Side truck had a "smoke screen" set up that put ATF into the intake for a good show. That engine had about 40,000 miles since a rebuild and it needed a head gasket, for some strange reason. I had a friend help me change out both. Those cylinders looked like they had 400 miles on them.
It was clean as a whistle and as hollow as they day I bought it. No issues there. I did put a smoke screen in this like the one I mentioned above. The difference was that it had good mufflers instead of blown out glass packs like the truck had. It did take a while to burn out of those mufflers. It was still fun though.
Rdnck84_03
Full Access Member
@XOLATEM after getting more info about the truck I believe it is less likely to be a diesel conversion. I still wouldn't rule out the TCM being incorrect or bad though since it was said to have been a "marketplace replacement".
@TheMadHatter I do not remember what year they started the third brake light ( I know that 95 has it ). I know you said earlier that you thought yours originally had it. If it did you need it get a bulb back in it or put a resistor in it so the TCM thinks there is a bulb in it. THE TRANSMISSION WILL NOT SHIFT CORRECTLY WITHOUT IT!
James
@TheMadHatter I do not remember what year they started the third brake light ( I know that 95 has it ). I know you said earlier that you thought yours originally had it. If it did you need it get a bulb back in it or put a resistor in it so the TCM thinks there is a bulb in it. THE TRANSMISSION WILL NOT SHIFT CORRECTLY WITHOUT IT!
James
Rdnck84_03
Full Access Member
Yes I do agree with this statement. After we got more information about the truck I was leaning more towards bad TCM. But I just went back and re read some and believe that @Black dawg already caught the issue.
I did miss this earlier, if you have the map sensor hooked to anything that makes vacuum on a diesel, that is your problem! It should be vented to the atmosphere. On these trucks it is not used as a MANIFOLD ABSOLUTE PRESSURE sensor, it is a BAROMETRIC PRESSURE sensor.
James
As pointed out already on a diesel it's not a MAF sensor but it is a BARO sensor. I have the Innova OBD1 code reader and the code listing shows up as a MAF error code in the Innova booklet. I had that code once so removed the sensor, cleaned the contacts, reinstalled and the code never reappeared. Definitely no vac line connected to the sensor. Maybe this was already mentioned but have you checked all the transmission connectors for loose wires or corrosion? Is the MLPS and associated linkage nice and tight?
Black dawg
Registered User
any progress on this?
Jesus Freak
Full Access Member
Hey @Nero , does this thread need "ending 2.0"? Maybe he rides off into the sunset with a Honda Big Red 250, leaving his truck on side of the road with the flashers on, thus confusing his transmission controller?
Similar threads
