I am manager at an auto pats store, i have a customer that is having some probelms fixing a 1999 F150 with 4.6.

It cranks but no start, there seems to be something with the grounds to the injectors, he has power to them but no grounds.

He had someone come and scan with a better scanner than he has and it came up with no TX input.

He has changed cam and crank sensors among other things, checked all the power grounds from the computer swapped the key/transponder still nothing.

So what provides the input to the computer to ground the injectors and does anyone have any ideas of where to look for a fix.

thanks

dave

 

Oppps!! Nevermind , I'm not a tech.

 

check all the fuses, or maybe the inertia switch under the passenger kick panel needs reset?

 

Your quite a guy to do this for a customer
The injectors are all powered from the 12 volt supply thru fusing.
Each injector's ground to operate it, is done individually in the PCM at the fire order sequence for the motor.
Your discription would be that of a PCM that is not switching the injectors.
Question is, is there spark at cranking?
If so, that leaves out the crank sensor as the source but does leave the cam position sensor because it controls injector timing.
At this point, a good tech needs to look at the system with a hi end scanner to determine where the failure is occurring.
Is it the harness, the cam sensor, the PCM etc.
Doing anything else is now guessing.
That's as close as I can get you to the logic of the problem.
I don't know what Tx means for the code. Need the P code number for me to interpet.
Good luck.

 

Check Central junction box: Fuse 2 (5A) Fuse 6 (5A) Fuse 30 (30A)
Hold down the trip/odometer reset button and turn the key to run. After about 5 seconds the odometer will read test. Release the button. It should go to gauge and the gauge needles will sweep and return to rest. Press and release till you see dtc. Read the codes after the dtc There may be some codes like B1600 or B1601 etc... Continue pressing and releasing till there are no codes. Only one at a time will show. There may be a PATS problem. Does the theft light flash with the key out of the ignition?

JMC

 

Since the PATS system works by shutting off the injectors (under computer control), start with it.

Does it prove out properly or does the THEFT light blink rapidly (failure) when starting is attempted?

Are there any aftermarket remotes or security systems installed?

Have either the instrument cluster or the PCM been replaced and this is the result?

Steve

 

He does have spark and it will run if some sort of fuel is put through the throttle body, until it is burnt up.
he has changed the PCM and nothing different from the original one, neither have been reflashed as of yet.
Not sure about the light blinking thing, I will be stopping there for my weekly visit in a couple hours and see where he is at with it.

thanks for the input so far.

dave

 

I would look here first for this the problem. In order and it's already been mentioned.

1. Fuel Pump fuse.
2. Fuel Pump relay.
3. Inertia switch - push to reset ( it works as a fuel supply circuit breaker)

 

If it'll run (or at least cough and sputter) on gas (or starting fluid) put through the TB, then we know it's not a spark issue, it's a fuel delivery issue. I'd be looking at the fuel pump fuses, inertia switch, and checking fuel pressure at the rail.

JMC and Bluegrass are on to something... if it was an ignition issue. But if it was an ignition issue, it wouldn;t run on fuel/starting fluid poured through the intake.

-Joe

 

He has installed a new pump, and filter, and a relay. Checked the inertia switch for power and continuity. Checked all the grounds from the from the computer. Checked the wiring under the fuse blocks for corosion.

I think he has come down to, like many here, the theft system. He has put in another key and transponder, he even tried to jumper around them, but still nothing changed.

The fuel pump runs for a split second, not the usual 2-3 seconds when the key is turned on.

It looks like there are only 4 wires from the transponder, has a white plug, anyone know if it is possible to bypass this just to try to isolate the problem to the key and related parts?

thanks

dave

 

The TX and RX circuits are the signal and return from the PATS transceiver to the instrument cluster. Without either of these inputs, the truck won't start. He needs to check the wiring from the transceiver to the instrument cluster; normally though, what happens is one of the two circuits is lost through the instrument cluster, normally a burn on the PCB of the cluster. The TX circuit number is 1215, and it'll be a white/light green wire at the transceiver. The RX circuit is 1216, and it'll be gray/orange. He needs to remove the instrument cluster and check both circuits from the PATS transceiver to the cluster. I've had to replace a lot of instrument clusters for this before.

 

Dude, focus on the PATS system first!

See my previous post for the reason WHY.

Steve

 

Listen to the last two replies.
The PATS and the PCM must 'talk' to each other on the transmit TX and the recieve RX leads.
That's the basis of the anti theft feature and why these trucks are hard to steal and give the owner the same hard time if a fault occurrs.
You can't jumper around because it's software based by data transmission over this bus lead pair..
Further, what's involved in software is the vehichle identification program block. If the bit is not set in this block by the PATS, it inhibits the motor from starting.
If the truck's dash has the ability, turn on the ignition and wait several minutes to see if the Theft lamp flashes a code. If yes, it is telling you that the PCM and the PATS can't talk to each other.
There should be a code found in the dash HEC test and a complimentary code in the PCM to match as a varification.
If you find this condition and not know what to do with it, it's dealer time because without knowing what is going on, you won't have a chance of fixing it..
Good luck.

 

An additional idea: A fault in the TPS that tells the computer the throttle is at 100% will also cause the computer to shut off the injectors.

Steve

 

Continued thanks,

I will print all of these suggestions off and give to him again on monday.