hi I'm having troubles with my 91 ford f250 351w, 60000miles.
MY engine is set up to run on duel fuel and my problems are the same either runing autogas or petrol.
so this is what happens,
engine starts fine runs smooth up to 2500rpm light load verything
is ok, above 2500rpm timming starts to retard rapidly, then by
3000rpm time has retarded to 30 degrees after A.T.D.C,
the engine looses power and misses,.
my mechanic has had the computer checked it's fine,
there are no error codes,
what should we look for next as I need my truck for work
In Australia the ford truck aren't as common as the u.s.a.

my trucks alternator went not long ago when driving home
the power surged up and down till the battery was flat but
I've had that fixed. The only other thing is I have a burnt out
fuel pump in the first tank , but the rear is fine and the problem is the same when switched over to lpg auto gas. just thought I'd
tell you this in case it comes in handy.

 

Dont rule out a plugged cat. converter. Acts very much the same way, they handle the small volume of exhaust at low rpms but can't at higher.
Also I have been told, (don't know if it's true) dual fuel operation on LP shortens the life of the cats.

Good luck!

Gene

 

yes I was thinking of that myself ,but my mechanic said it did the same when he pulled the cat off.

 

Could also be a clogged muffler. Not very common, but possible. I would do a voltage check at the pump, pressure check at the rail, volume check at the return line. Check for a loose timing chain and if your truck get timing signals from the crank, check the outer balancer hub. Does yours have a knock sensor?

SL

 

if he un bolts the exhaust and it still does the same, tell him to check timing at base idle. if it is off, it may have jumped time. it may be the ignition module or ecu pulling too much timing and it takes a big misshap to throw a code. did he just try to pull hard codes? Did he do a KOER and the KOEO test? pull off the distributor cap and slowly turn crank with a pull handle one way and then the other. if there is excessive crank movement before the ign. rotor moves you need to replace the timing chain. EEC-IV and EEC-V systems may go along time before throwing a code, most of the time you have to track it down the old fashioned way.

 

I would have to ask what codes he did try and pull,
there is no knock sensor ,
he said he looked at the timing chain and it was fine.
but I will check it the way you said ,
thanks so far for the replies

 

A check of the book does indeed show no knock sensor as you say.
Suggest the SPOUT plug be removed and test again for what the timing does.
If it stays firm, then the the problem is computer related and I have no idea from there.
Your engine control system may be a bit different on trucks exported to your country.
Good luck.

 

the computer has been sent away and checked ,everything in it
is fine.

 

according to the car computer doctor who pulled it apart and
tested the computer theres nothing wrong with it

 

The computer calculates and changes the ignition timeing by applying it back to the TFI, then fires the coil.
TAKE the SPOUT out and see what the timing does.
It is either the computer or the TFI. There is nothing else controlling the timing.
Sensors only modify the base timing that is set by adjusting distrubutor position to the basic 10* inital setting.
A possible way to be able to use the truck is to pull the Spout out and set the dist. timing to about 20* and run it at that static fixed setting until the fault is found.

 

thanks for the reply
do you mean if I do what you suggest it will cut out the computer
from working

 

The spout plug removed, isolates the computer from making any timing changes.
You take away the computer's ability to change the timing by doing this.
By setting the base timing up to about 20 degrees, this will allow you to still start the engine and drive it with reasonable power so you can use the truck, while troubleshooting in off hours.
This can be done "assuming" the TFI and the pickup are fault free.
The PIP will fire the coil through the TFI directly at whatever base timing is set.
Normally you will see about 22* in a normal system, at idle, hence (setting base timing to 20* with Spout removed) should be able to run the engine enough to be useable for short runs. Believe it, it is done all the time. It's called fixed timing! Start the engine and time it with a light.
Please read carefully!.