Why does my truck run better with the MAP sensor unplugged - Ford Truck Enthusiasts Forums



1999 - 2003 7.3L Power Stroke Diesel  
Sponsored by:
Sponsored by:

Why does my truck run better with the MAP sensor unplugged

Reply
 
 
 
Thread Tools Search this Thread
  #1  
Old 05-24-2017, 04:06 PM
Mydiesel250's Avatar
Mydiesel250 Mydiesel250 is offline
Senior User
Thread Starter
 
Join Date: Mar 2008
Posts: 210
Mydiesel250 is starting off with a positive reputation.
Why does my truck run better with the MAP sensor unplugged

I've been beating my head trying to figure out the problem with my wife's truck. Today I was changing out some sensors and still no changes. The truck is extremely sluggish from a stop, smooth , but sluggish. Runs fine other than that. I unplugged the MAP sensor and the throttle response is so much better. I assumed the MAP sensor was going bad so I did a quick swap from my truck to hers and no difference. No Matter which sensor is installed it only loses its sluggishness while unplugged. The line is clear, back pressure sensor is new and. Tube and ports cleaned. Mechanical and electronic boost gauges read 18-20 psi WOT. Anybody have any ideas to throw at me?
Thanks
Reply With Quote
  #2  
Old 05-24-2017, 11:41 PM
Karlow Karlow is offline
Senior User
 
Join Date: Nov 2016
Location: SGV SoCal
Posts: 369
Karlow is gaining momentum as a positive member of FTE.
That is strange, with that level of boost it sounds like its not get fuel unless the map is not connected. When you disconnect it, I assume it's at atmospheric pressure (electrically attached, but not attached to the hose).
Reply With Quote
  #3  
Old 05-25-2017, 12:31 AM
Mydiesel250's Avatar
Mydiesel250 Mydiesel250 is offline
Senior User
Thread Starter
 
Join Date: Mar 2008
Posts: 210
Mydiesel250 is starting off with a positive reputation.
Ya know, after all that swappin back and forth I didn't even think about maintaining the electrical connection and disconnecting the vacuum line. I have been stewing all night and will certainly try this in the morning. I may try disconnecting, as well as capping the line just to see how it acts during both scenarios.
Thanks
Reply With Quote
  #4  
Old 05-25-2017, 06:37 AM
Tugly's Avatar
Tugly Tugly is offline
Post Fiend
 
Join Date: Jan 2011
Location: Columbia River
Posts: 16,927
Tugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputation
You may want to look at your 5V reference with the MAP plugged/unplugged. Maybe some other sensor is acting up, and the MAP being plugged in is the proverbial straw on the camel's back.
Reply With Quote
  #5  
Old 05-25-2017, 05:22 PM
Mydiesel250's Avatar
Mydiesel250 Mydiesel250 is offline
Senior User
Thread Starter
 
Join Date: Mar 2008
Posts: 210
Mydiesel250 is starting off with a positive reputation.
So unplugging the boost line makes it run rough, capping the boost line makes it run flat and slow with zero power throughout the rpm. Full defueling I assume. Here's what I did , not the best way, but, I left the electrical connected to the MAP, and ran an air hose from the nipple to compressor , regulated around 16psi. , cranked the truck, with about 16psi to the MAP, and put it in drive and it jumped out of its pants with power. So I still don't know what's going on, but is there a way to get around this so the damn thing just gives it the fuel like it would with a normal reading?
Reply With Quote
  #6  
Old 05-25-2017, 05:22 PM
Mydiesel250's Avatar
Mydiesel250 Mydiesel250 is offline
Senior User
Thread Starter
 
Join Date: Mar 2008
Posts: 210
Mydiesel250 is starting off with a positive reputation.
Plug shows 5v
Reply With Quote
  #7  
Old 05-26-2017, 12:22 AM
pirschwagon pirschwagon is offline
Senior User
 
Join Date: May 2016
Posts: 480
pirschwagon has a very good reputation on FTE.pirschwagon has a very good reputation on FTE.pirschwagon has a very good reputation on FTE.
Just off the top of my head....

The 5vRef Circuit need to be tested both cranking and running: Maximum, Minimum, and permissible drop.

Minimum Voltage - 3.40 vdc / 0.3 vdc Cranking Maximum Drop / 0.1. vdc Running Maximum Drop

I would look at these sensors PID's:

BARO/MAP/EBP - KOEO, they should be closely to within 5 PSI of each other.
Reply With Quote
  #8  
Old 05-26-2017, 07:13 AM
Tugly's Avatar
Tugly Tugly is offline
Post Fiend
 
Join Date: Jan 2011
Location: Columbia River
Posts: 16,927
Tugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputationTugly has a superb reputation
Has it always done this? What are you comparing "sluggish" to?
Reply With Quote
  #9  
Old 05-26-2017, 08:01 AM
ExPACamper ExPACamper is offline
Polkamatic Poster
 
Join Date: Mar 2015
Location: Blairsville, Pennsylvania
Posts: 4,119
ExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud of
Quote:
Originally Posted by Mydiesel250 View Post
So unplugging the boost line makes it run rough, capping the boost line makes it run flat and slow with zero power throughout the rpm. Full defueling I assume. Here's what I did , not the best way, but, I left the electrical connected to the MAP, and ran an air hose from the nipple to compressor , regulated around 16psi. , cranked the truck, with about 16psi to the MAP, and put it in drive and it jumped out of its pants with power. So I still don't know what's going on, but is there a way to get around this so the damn thing just gives it the fuel like it would with a normal reading?
So if I understand correctly, the problem is your turbo port isn't getting pressure to the MAP sensor, right?

You've confirmed this by running with MAP plugged in and she runs flat (probably limited to about 2k rpms), and then by running with MAP plugged in and artificially supplying 16psi to the MAP.

Additionally, your Boost gauges are reading pressure. WHERE are they connected?

It would see simple that either your tube on your spider is clogged (never heard of one, but pop off the spider and check), or your tubing is clogged up.

I used a piece of 1/4" fuel line to replace mine that was a little short (I broke my MAP nipple installing CAC hoses over top of it ).

ALWAYS be sure to blow through your lines and tubing before using them. We have mud dobbers around here. I've found more than one situation where they have been inside a line and went flying when I use the air compressor to blow them out

With my broken MAP sensor plugged in, that is how my truck ran last week. Unplugging the MAP sensor forces computer to use a default 29.4psi value (IIRC) and she runs like a beast! Replacing my sensor with a MOTORCRAFT OEM MAP sensor and a new line fixed it.

May you have the same success
Reply With Quote
  #10  
Old 05-26-2017, 08:33 AM
Mydiesel250's Avatar
Mydiesel250 Mydiesel250 is offline
Senior User
Thread Starter
 
Join Date: Mar 2008
Posts: 210
Mydiesel250 is starting off with a positive reputation.
Pirsch- I will check those numbers here in just s bit. Thanks

Tugly- it has always been like this, less noticeable when it was completely stock. These things usually feel like dead whales from stock after driving a tuned one for 10 years. I have the same truck as my wife , the identical aftermarket parts- intake de-muffed, superchips 1805. After I hooked up the superchips it was obvious that the sluggishness became more pronounced. It feels exactly like limp mode for the first 2500rmp , then like a power band kicks on and it drives like normal. This only happens from a dead stop. I'm used to my truck and when I drive hers I catch myself leaning forward like a jackass pulling out and forgetting that it doesn't get up and go. Lol

ExPa- I'm not opposed to buying a new map, my only concern is that I swapped my MAP , boost line, and EBP sensor from mine to hers. No change , put hers on mine and my truck ran like it always does. Makes me assume those parts are still ok, I'm certainly no expert though. My mechanical boost gauge is T into the map line, and the electronic one I believe reads from the MAP, but I'm not completely sure on that.
Reply With Quote
  #11  
Old 05-26-2017, 09:10 AM
ExPACamper ExPACamper is offline
Polkamatic Poster
 
Join Date: Mar 2015
Location: Blairsville, Pennsylvania
Posts: 4,119
ExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud of
Quote:
Originally Posted by Mydiesel250 View Post
ExPa- I'm not opposed to buying a new map, my only concern is that I swapped my MAP , boost line, and EBP sensor from mine to hers. No change , put hers on mine and my truck ran like it always does. Makes me assume those parts are still ok, I'm certainly no expert though. My mechanical boost gauge is T into the map line, and the electronic one I believe reads from the MAP, but I'm not completely sure on that.
I wouldn't buy a new one. I did because I broke mine. I *would* suspect and replace the line from your tee to the MAP. That is, if your tee'd-in gauge is reading properly. Be sure to check that first.
Reply With Quote
  #12  
Old 05-26-2017, 10:33 AM
Mydiesel250's Avatar
Mydiesel250 Mydiesel250 is offline
Senior User
Thread Starter
 
Join Date: Mar 2008
Posts: 210
Mydiesel250 is starting off with a positive reputation.
Ive replaced the hose from the spider to map with clean new hose to bypass any possible leaks at the T . No change still, I still need to check the volt parameters at the plug during cranking. Would a boost fooler achieve the same thing that my manual PSI to the map sensor, but handling it from the electrical side, or is that only good for OVERboost?
Reply With Quote
  #13  
Old 05-26-2017, 11:11 AM
ExPACamper ExPACamper is offline
Polkamatic Poster
 
Join Date: Mar 2015
Location: Blairsville, Pennsylvania
Posts: 4,119
ExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud ofExPACamper has much to be proud of
Quote:
Originally Posted by Mydiesel250 View Post
Ive replaced the hose from the spider to map with clean new hose to bypass any possible leaks at the T . No change still, I still need to check the volt parameters at the plug during cranking. Would a boost fooler achieve the same thing that my manual PSI to the map sensor, but handling it from the electrical side, or is that only good for OVERboost?
I haven't used one. Are you talking about a physical (regulator style) fooler, or an electrical (resistor or something) fooler?

If it's electrical, pull it out of the system to troubleshoot. What brand or style is it?

Maybe someone with more experience with boost foolers will be able to be helpful here?
Reply With Quote
  #14  
Old 05-26-2017, 11:21 AM
Hussler's Avatar
Hussler Hussler is offline
Postmaster
 
Join Date: Sep 2007
Location: Medford Oregon
Posts: 3,639
Hussler is a name known to allHussler is a name known to allHussler is a name known to allHussler is a name known to allHussler is a name known to allHussler is a name known to all
Steve, have you checked the EOT sensor with a scanner yet? It could be reporting cold all the time. If no scanner just unplug it and PCM will assume a hot engine. Or you can just measure the resistance of the sensors to compare. EOT has more effect on fueling and timing than boost ever does.
Reply With Quote
  #15  
Old 05-27-2017, 09:32 PM
retiredsparky retiredsparky is offline
Elder User
 
Join Date: Sep 2011
Location: Vancouver
Posts: 966
retiredsparky has a great reputation on FTE.retiredsparky has a great reputation on FTE.retiredsparky has a great reputation on FTE.retiredsparky has a great reputation on FTE.
The ref voltage seems fine at 5 volts, maybe the return wire has a corroded connection at the PCM. Is there a "chip" plugged into the PCM? Sometimes the copper foil connections that the chip plugs into can become corroded over time, especially if there is windshield leaking.

If you are really into torture, swap your PCM into your wife's truck. The easiest way to get to the PCM is to cut a piece of plywood about 18" X 72" and lay it in the drivers door of the truck and support the outer end with a stool or ladder, so you can reach the mounting bolts for the PCM next to the parking brake. (You have to disconnect the harness under the hood first).

Another more likely location for a bad connection would be the 42 pin connector at the driver's side valve cover. Corrosion there is pretty common. Good luck!
Larry
Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Truck Runs Great When I Unplug the MAP Sensor Bondsman Chris 1987 - 1996 F150 & Larger F-Series Trucks 8 04-07-2017 09:30 PM
2002 7.3 43psi ebp all the time 7.3stroker2 1999 - 2003 7.3L Power Stroke Diesel 5 10-14-2016 08:31 AM
MAP codes BradSmith-7.3L 1994.5 - 1997 7.3L Power Stroke Diesel 4 02-16-2016 07:12 PM
Transmission Troubles squeaks07 1999 - 2003 7.3L Power Stroke Diesel 6 02-04-2016 07:14 PM
Please help Mwvwaw 1987 - 1996 F150 & Larger F-Series Trucks 1 01-08-2016 03:05 PM


Go Back   Ford Truck Enthusiasts Forums >

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump


All times are GMT -5. The time now is 02:47 AM.