(Working on truck in SIG)

I am still trying to get my ignition 100% working after replacing the TFI and Distributor. Code 0300 Random misfire keeps showing. The truck will rev but stumble and pop with an impossible to ignore miss. It does not want to move it's own weight. Plugs #2 and #4 look sooted. I have checked all wires for fire (new and check good) and tried different plugs. Still the same result. Timing advance appears to work when engine is reved.

Not sure if the plugs are not firing at the right time or the injectors not giving fuel? New fuel filter, Fuel pressure steady at 55PSI. I have dual tanks. Changing tanks has no affect. Removed vacuume to fuel pressure regulator. No raw fuel pressent.

I did get a bad TFI from AutoZone. Could this cook the computer? Does it sound possible to have a bad fuel management circuit affect only the two cylinders? I would think that it would screw up the whole system...

When the original TFI went out, the truck fired at odd times and kicked back hard enough to blow some vacuume lines off. The checklight came on but it ran good for a few miles so I could pull off the road. I smelled a gunpowder smell in the cab and thought it was exhuast from the kickback coming out the vacuume lines. I have heard that the computer will make a smell when it cooks. Now I am wondering if this was the smell? I would not think the truck would run at all with a cooked computer.

When the truck starts it will try to turn and then act like a high compression engine and hang for a second and then turn and fire. Never did that before. Like the timing or fuel or both is off.

Anybody have a bad crankshaft position sensor? I have the harmonic balancer pully/timing marks that change all the time. The ring with three tabs for the crank position is behind the harmonic balancer. Does anybody know if this ring is held in place by a key or is it possible to shift position? Does anyone know how I can verify the position of this ring? IE Does one tab line up with the position sensor when #1 piston is at TDC? Does anybody know exactly what this position information is used for? Is it for spark, fuel or both?

Thanks for any ideas to this mystery...

 

No crank sensor on the 4.9 to my knowledge. Is there still a vaccum advance on the 96. I used to own one but cannot remember. If so I'd try twisting the dizzy and set timing old school. Double and tripple check your plug wiring find TDC on #1. Start simple.
TFI may be bad if you forgot dielectric grease on the back.

Did you remove the spout conector to set timing?
Have you checked the ignition control modual?

 

TFI Trouble shooting.

Ford Ranger/Bronco II TFI Ignition Diagnostics

 

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The crankshaft position sensor is located at the 10:00 position as you face the crank pully. Timing advance is done electronically and I have verified the timing many times. Retested the TFI module at three different stores. It passes the test with plenty of dielectric grease. Since it is lifetime warranty I got another new one, but haven't had time to install it.

 

Harte3,

Thanks for the troubleshooting link. I printed the worksheet and will try to pinpoint the problems this weekend.

 

You are quite welcome. I picked that up off another post by someone here not too long ago...figured it would come in handy so I filed it.

 

According to haynes you have no crank sensor for your ignition. Its a;-Hall efect, Profile ignition pickup. All self contained in the distributor. Haynes may be wrong as the 96 4.9 was the only year to have OBD2. I recall my 96 f150 having 97 calipers in the front!
I read both the igniton and the wiring diagrams. I'd check your ignition control modual.

 

flipklos,

That is part of the mystery. I am sure that it has a crank position sensor. I can't find any information on it as far as trouble shooting goes. The local library is closed for rentivation so the motor manuals aren't available. I can't determine what the information is used. Is it for fuel management? Ignition? Or perhaps both. Or maybe it does have to do with being the first year for OBD-II. I thought about unpluging it and see how that effects the way the engine runs.

 

Why not buy the ford wiring diagram? Ford still had them a few years ago. If not someone sould have one on the internet. Actualy when I was working on my 85 I just borrowed a copy from the mechanics in the local ford garage.
May help you figure stuff out.

 

FINALLY, I can put this thread to rest. After changing the TFI (again), resetting the computer and changing a few new fuel fouled plugs the ole 300 is again running smooth as can be. I bought a Scanguage II for troubleshooting and now look forward to using the computer to dial in the timing as well as the MPG computer.

 

The scantools are worth it if you do all your own maintance. I've an obd 1+2 tool. Real lifesaver. Glad she is puring again.