Dash installed = no start?
Thread Starter
|
Senior User
Joined: Jul 2009
Posts: 201
Likes: 0
Dash installed = no start?
I remember something about these trucks and needing the dash to run right or something, don't remember what it was or if it actually existed but.... If my dash is installed, it cranks over and half fires like it's starving for fuel, but unplug the dash and it'll start up like it was out of fuel then run. Dash in, it'll start for a couple seconds maybe then stall, dash unplugged, it'll run all day although not as smooth as it should. Does anyone have an idea of what's going on?
97 F-Superduty 7.3L 5 speed
97 F-Superduty 7.3L 5 speed
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
Hmmm, that's an odd one. One thing that definitely could affect the way the truck runs is the Baro sensor that is part of the dash assembly. It is located more or less directly below the steering wheel under the dash. It looks like a square relay with a round connector on it. That would be one thing to check anyway.
Thread Starter
|
Senior User
Joined: Jul 2009
Posts: 201
Likes: 0
It's in a project truck, Have had it running well for a couple days, today I'm tidying up loose ends and installed the dash, push truck outside and go to start it and this happened..... took a while to suspect the dash but pulled the plugs out and it fired up, but now it's grumpy. Yesterday it fired up and ran nice with no dash.
Been reading about no starts due to cam sensors..... and computer not seeing a tach signal and not fueling engine. If removing dash enables a "limp mode" or something to bypass the CPS, it would be where I start. Just can't figure out the rough running today vs yesterday all due to installing dash.
Been reading about no starts due to cam sensors..... and computer not seeing a tach signal and not fueling engine. If removing dash enables a "limp mode" or something to bypass the CPS, it would be where I start. Just can't figure out the rough running today vs yesterday all due to installing dash.
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
The CPS wires directly to the PCM so I can't see that being the issue. The only things I know of for sure that you eliminate by unplugging the dash are the BARO sensor and the 2 sensors on the throttle pedal (TPS and IVS).
Did you install the whole late model dash and wiring harness or was it a cut and splice type of job? If the VREF signal was incorrectly spliced and isn't at the full voltage that would cause running issues.
Did you install the whole late model dash and wiring harness or was it a cut and splice type of job? If the VREF signal was incorrectly spliced and isn't at the full voltage that would cause running issues.
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
Are all the dash lights and things from the OBS donor connected to the harness? Ford has a bad habit of using the filament for a given bulb as part of the sensor circuit for a sensor. I would have to look at a schematic again to see if that may have been the case for something here.
Thread Starter
|
Senior User
Joined: Jul 2009
Posts: 201
Likes: 0
Yup, everything OBS is in the project truck, found the Baro sensor, is there any way to test it? Also, peeled wiring cover away from throttle pedal, and noticed all the wires had been tapped- there's like an inch of wire sticking off of each wire, not sure what that was all about.
Trending Topics
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
I'm not sure whether you can test the baro sensor or not, but you can just unplug it and the PCM will default to a standard value and the truck will run without it. Id unplug it and give that a try.
As for the wires tapped into the throttle wiring, I would wager that someone had set up a high idle on it. I'd clean that wiring up and tape things up good while you're in there, but I doubt that was your issue. I'm not home this weekend or I would have access to a lot better information.
As for the wires tapped into the throttle wiring, I would wager that someone had set up a high idle on it. I'd clean that wiring up and tape things up good while you're in there, but I doubt that was your issue. I'm not home this weekend or I would have access to a lot better information.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
Thread Starter
|
Senior User
Joined: Jul 2009
Posts: 201
Likes: 0
If the Baro is unplugged, would that default the same as having the dash unplugged? I'm trying to get a buddies truck over so i can borrow his sensor. The wires on the pedal confuse me because the truck has the factory high idle box under the dash, although it was a work truck with a winch so who knows.
When you say the dash lights are part of the circuit, are you saying that if a dash light burnt out that it could actually cause it to run differently? Or that say.... a cheap bulb could cause a different ohm or voltage reading in a circuit kind of thing?
When you say the dash lights are part of the circuit, are you saying that if a dash light burnt out that it could actually cause it to run differently? Or that say.... a cheap bulb could cause a different ohm or voltage reading in a circuit kind of thing?
Lead Driver
Joined: Mar 2006
Posts: 5,111
Likes: 1,544
From: western SD
Postmaster
Joined: Sep 2007
Posts: 4,195
Likes: 6
From: Medford Oregon
Agree ... ^^^ ... VREF is + 5 volts from the PCM. It supplies power to all sensors. In your case you can measure it at the TPS, IVS or any other sensor. If it's missing the truck won't start or run.
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
With the dash connected, correct?
Yes, unplugging the BARO would likely give the same default reading to the PCM as having the dash unplugged. I would definitely take a look at that. Just unplug the thing and see how the truck runs.
Yes, unplugging the BARO would likely give the same default reading to the PCM as having the dash unplugged. I would definitely take a look at that. Just unplug the thing and see how the truck runs.
Thread Starter
|
Senior User
Joined: Jul 2009
Posts: 201
Likes: 0
Yes, with dash installed, just repeated to be sure, 5.05V at pedal, had it on charger all night so don't know if that changes anything (0.02V). Changed the Baro sensor with one from a friends truck last night, no change in my truck with his, and no change in his truck with mine..... If you take the dash in/out part out of the equation, truck seems like it's starving for fuel. So much actually that I'm pulling the box and pulling the sender out and taking a look. It's actually gotten worse now and the dash no dash thing isn't having the same effect, BUT the other day it was the difference between starting and not starting, no questions. It's still getting enough fuel to smoke and half fire but even when it ran, it had a lack of power like less fuel than it wanted, do not understand what the difference with the dash was tho.