Off Roading Forums banner
1 - 8 of 8 Posts
G

·
Discussion Starter · #1 ·
I have been following this group for a while, and have seen several people who have similar problems... I first experienced the problem when towing a trailer up a mountain pass with the A/C on. After sitting for about 15 minutes, it finally restarted. After completing the trip at 55 mph with no A/C, I changed the in-tank fuel pump and fuel filter (I could hear the high pressure pump running). The problem now occurs often when the engine is warmed up, the outside temperature is hot, the A/C is on. Under these conditions, the truck dies as soon as I hit a fairly large bump, and will not restart. I checked the fuel pressure, and it is within the range indicated in my manual (35-40 psi, I think) and checked that fuel is pumping (there is a valve on my pressure tester), so I don't believe that it could be vapor lock. The part that I can't figure out is that if I spray starting fluid into the air cleaner, and start it and let it idle until the starting fluid is used up, then it will continue to run normally. The only trouble code is 87 (fuel pump circuit), which I believe is because it appears the previous owner bypassed the eec to the fuel pump relay by grounding the side of the relay that would go to the eec. This causes the pumps to run whenever the ignition switch is on, similar to grounding the fuel pump terminal on the DLC. The stored trouble codes are 14,18 which apparently relate to the ignition system, 31, which relates to the EGR valve position sensor (which I recently replaced), and 61, which Engine Coolant Sensor.
I checked the resistance of the coolant sensor, and it tested to around 30k ohms warm. I have also tried bypassing the fuel pump inertia cutoff switch, but the problem still occurs. I read some earlier posts that mentioned the ignition switch disengaging when hitting bumps or turning a corner, and another thread that related warm temperature stalling to the coil, and others that claimed the TFI could cause "flaky" behavior. One detail that I omitted was that I didn't encounter this problem before I recharged the A/C, so I assumed that it was related, and found out that it will do it even with the A/C off as soon as I get it off the pavement and onto a bumpy dirt road, which pretty much rules out any four-wheeling until I can get this straightened out. If anybody can offer any help I would greatly appreciate it.
 
G

·
Discussion Starter · #2 ·
It sounds like you know your truck pretty well but maybe a dummy could help!
I have the same problem with my 85.
A little word of mouth history first...I was informed by a mechanic that 85 and 86 had an early system that was very difficult to diagnose and fix.
Now to my input...I have a little knowledge about Porsche F.I. and when that problem occurs it is the hot start solenoid. I don't know if our Fords have that thing too, but it makes sense that something needs to be in there.
When the engine is off when it is warm, the fuel evaporates is my theory. The hot start valve feeds extra gas to the cylinders to give it enough gas to start. (Same as a clod start valve).
 

·
Registered
Joined
·
1,444 Posts
My vote goes to your TFI module or the coil, late addition there, because the AC compressor is right next to them & like my 86 , that compressor gets really hot! pick up spares from a wreck & see if it goes away...
 

·
Registered
Joined
·
1,147 Posts
An 86 eh ?

This little tid bit cost me plenty to find out. Replaced most of my ignition system before we found it. Used to be flyin' down the highway smilin' when I'd hit a bump and coast to the side of the road dead. I'd replace a part, pray to the East, slam the hood and it often started again. Months would go by, then another bump and same thing.

There's an orange wire off your solenoid with a fusible link. Inside, unseen to the naked, bleary, pi$$ed off eye, there was an almost rotted away wire. Hit the right bump, no connection. Slam the hood hard enough, connection re-made, back on the road again. Talk about a relief to find that one !!!

If it ain't that, I'd agree with the others always suspect the coil if it happens hot.

Good luck

Sixltre
 
G

·
Discussion Starter · #5 ·
Thanks for all your input, it has given me some new directions to look in. I looked in my manual, and didn't find any mention of a hot start valve or circuit, which leads me to wonder if the eec always uses some set of preprogrammed parameters for starting, or if it relies on the inputs from the sensors?

I looked at the orange fusible link, which I found under the blower, behind the starter solenoid, and wiggled it with the engine running, with no effect. The only orange fusible link that I could find in my wiring diagram was for the rear window defroster--is there another one that I am missing?

Finally, I have some TFI questions: When you guys say that the TFI is probably faulty, are you referring to the ignition module or the whole system? It looks to me like I would have to pull the distributor to change the module, Is that the case?

Another question I have is why does it start with starter fluid, if the problem is with the ignition? I have noticed that about 50% of the time it preignites when starting with the fluid (sounds like pinging) could it be that it will compression ignite with the starter fluid (given the high engine temperature when I encounter this problem), and once the engine is running, the system recovers?

One other thing... I connected a voltmeter across one of the fuel injector leads while it was in this no-start condition, and had my wife crank the engine. There was no indication of voltage whatsoever. This would indicate to me that the injectors are not receiving the fire pulse from the eec. Which leads me to the question, how does the eec time the fire pulses for the EFI? Does it rely on input from the TFI? I looked into buying an ignition module, and it is only $32 at autozone, so I don't mind changing it, but I really would like to understand WTF is going on, since the problem is so intermittent and I won't know if it is fixed since I don't have a 100% foolproof method of reproducing the problem besides driving 20 miles out of cellphone range in 100 degree AZ heat.

Thanks
 

·
Registered
Joined
·
1,444 Posts
I recently replaced the coil on MY 86 bronc just for the heck of it and for the satisfaction of knowing I have a Hi-Po coil in it
, i bought a crane coil, anyhow, when i removed the original, i looked on the back and the plastic casing was cracking all too sh#t. If yours is the original on an 86, its gonna blow-replace it. The TFI ign module screws onto the front of the distributor with two tiny torx screws which require a special thumb torx screw tool*lysle* brand- i think thats how you spell it & its avail at any auto parts store(about $6.00). No you dont have to remove the distributor, just make sure you put a thin film of dielectric grease behind the new one & the dist. hence: TFI= THIN FILM ignition.
If the engine is already HOT, starting fluid will make it fire no matter whats not working and it will also destroy your motor if you dont solve your problem soon!


I dont think that voltage test on your injectors is gonna solve anything as the voltage to them varies, have you ever replaced the filter in the fuel reservoir behind the transfer case skid plate & the in-line cannister filter? Also, have you checked for fuel pressure *after * it stalls?
Your 86, just like mine also has a fuel pump under the driver side door behind the frame rail, do you hear it hissing with the door open when you turn the key to start it after it dies? I once had a starting prob & the terminals on that pump were corroded from mud slinging on em since they are right behind the driver side front wheel.

Also, for a test try this next time it stalls- when you attempt to restart it, turn the key from off to run at least 6 times for a few seconds at a time(this charges the high press pump) and THEN see if it will crank over, if it does its your fuel system...
 
G

·
Discussion Starter · #7 ·
Thanks everybody for all of the input--I changed the ignition module and coil this weekend, and the problem hasn't been back. I'm not 100% convinced that the problem is solved, since it has been known to disappear for weeks at a time. The truck does seem to run a little better, but that could just be wishful thinking.
 

·
Registered
Joined
·
5,301 Posts
Injector voltage

The EEC varies the pulse width & frequency of the GROUND signal to the injectors - that's on the wires that are different colors (like some injectors have a red & a brown, and others have a red & a white - red is always hot when the key is on, and the brown & white get pulsed to ground). It knows what frequency & timing to use based on the PIP (sensor in the distributor), not the TFI (THICK-film ignition), and it uses the pulse width programmed into it for the variety of other sensor inputs.

OK In English
: you should check the voltage across the 2 wires of one injector; not from either wire to the battery or to ground.
 
1 - 8 of 8 Posts
Top