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Truck stalls when warmed up, won't restart, and has fuel smell?

8K views 26 replies 9 participants last post by  TheUnforgiven 
#1 ·
I will try to keep this as brief and to the point as possible, but I want include as much pertinent info as I can, as this is a truck I just spent 2 months working on and I need to get this thing sorted out soon, so please bear with me.

I bought my 91 5.0 in October. I drove 4 hours to see it. When I test drove it, everything seemed alright. After negotiating a price and handing over the cash, the seller walked across the parking lot to a gas station to wait for his wife to pick him up. Before heading out, I decided it was a good idea to stop by said gas station to fuel up before the long trip home. So, after filling up with fuel... the truck I had literally just paid for wouldn't start. It would just crank and crank. It also had a fuel smell under the hood. The seller came out and while he seemed surprised, I'm sure we'd all have our doubts to his sincerity in that situation... anyway, I had spent a long time looking for a Bronco, and this was unquestionably the best one I had found in my price range, and I wanted a Silver Anniversary, so I put a few bottles of whatever the gas station had as far as fuel system treatment in there, (I think it was STP) and kept trying. Eventually he was able to get the truck running, and the only thing he really did was throttle it. However, it would stall immediately unless he kept giving it some gas. So I hopped in, and after a few minutes holding the truck at 2000rpm, I was able to slowly bring the truck down to idle. But as soon as I shifted into Drive, it stalled. Again and again, same thing. After multiple tries, the truck FINALLY decided to keep running, and I was able to make the 4 hour drive home, without stalling.

When I made it home, I shut the truck off, and waited not even 5 minutes, and wouldn't ya know, it wouldn't start. The next day, in trying to go with the least intrusive approach, I tested and cleaned the IAC and the truck started right up (cold). It still, however, acted like it wanted to stall when shifting from Park to Drive, or Reverse. I knew this must be a relatively common problem on Broncos, because 2 of the 3 Broncos I test drove had the same symptoms. So I did a lot of searching on that subject, and found varying remedies. Some said IAC, some vacuum leak, some suggested that the trans filter could have dropped out, and I also read that the TPS could be a potential cause.

Upon inspection of my TPS, I found the insulation on the wires was chaffed, exposing bare wires. It was also kinda dirty and oily, and I found a new BWD TPS on eBay for $20 shipped, so I figured I might as well replace it. While I was waiting for it, well, one thing kinda led to another and I ended up cleaning the upper and lower intakes, painting them, and deciding to swap in some GT40P heads, among other associated parts...(so much for my least intrusive method...)

ANYWAY, after 2 months working on this thing, I was finally able to turn the key on it today. It started right up, everything looked good, and with the exception of multiple leaks from the pre-existing hacked together y-pipe, it ran great. It was idling at a rock solid 800rpm, and I was letting it get up to operating temp. Well, after about, I dunno 10 minutes maybe, it acted like it was going to stall, but didn't. Then not even a minute later, it did stall. I got back in the truck and tried to start it, but it just cranks... and there is a smell of fuel under the hood. I can hear the fuel pump kick on when I turn the key on.

If someone could help me out on this that would be great, I am really stumped here. I've also replaced the old injectors with the newer 4-hole style, fwiw.
 
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#2 ·
I just did a fresh rebuild myself with similar symptoms.
Have you checked fuel pressure yet. Rent a guage and attach to
Fuel rail, key on check pressure then turne key off and see if it bleeds down.

My case: I cleaned up some injectors from a 99 explorer they seem fine even when I ran air through it. First start up 3 of them stuck open and I could not
Start or idle and had over a gallon of fuel in oil and almost melted the cats.
 
#3 ·
Classic TFI symptoms. get hot, stall out. cool down, wham it has spark again.
 
#9 ·
A guy I work with suggested the same thing. I did some more research on the topic, and found enough evidence to feel somewhat confident... enough to hang a part... :shrug I picked up a BWD TFI CBE24 (thanks to this FSB thread) at O'Reilly for $56.99 with a lifetime warranty, and used "Arctic Silver 5" thermal compound I picked up from Radio Shack for like $12 after reading this thread on the Corral.

The '92 Service Manual says to "coat metal base plate of TFI-IV ignition module uniformly with silicone compound, approximately 0.79mm (1/32 inch) thick." Since I couldn't really discern 0.79mm of paste, I just went with plan B and used the whole tube. There isn't much in there, and it goes on pretty thick, so by no means was it a ridiculous amount.

After installing the new TFI module, I got the truck up and running. I got it up to operating temp, and everything seemed good. Since I had to remove the distributor to swap out the TFI, I decided to go ahead and set the timing following this FSB thread. Again, so far so good, but after setting the timing I was about done for the day, and I still have a decent exhaust leak from both collectors and my hacked up y-pipe. I did order a new y-pipe from Jeg's, so I should get that hopefully tomorrow.


I'll try to do some more testing tomorrow too, and see if it stays running. I do have a CEL, but I'm pretty sure that's from all the coolant that may have gone down into the y-pipe while doing my head swap...... But yeah, I obviously will try and pull codes as soon as I can.
 
#5 ·
OMP"S post sure sounds similar to the OP's don't it? :)
Anyway, cool thread and x2 everything so far. :)

The most likely suspects are the MAP sensor and the IAC.
I have never found cleaning an IAC to work well or long.
I have no experience with a bad-MAP and the only bad-TFI was in the late 90's.

But cleaning the IAC, now that you mention it, didn't-work-out-so-good for
me 3 out of 3 times. :) So, bought a new one and it's been acting right for
about a year now. Maybe they need -preventive maintenance- and the
cleanings not put off 'til it fails?

Couple things for sure on my 3 used IAC's was all three acted-bad differently! :)
And after cleaning 'em and swapping a bad-low-resistant coil off one of those
it definitely made a change in how they acted. They acted "better" for sure
but not-all-the-right like the new one did (and has).

My bet's on OMP tho. ;)
But that's because I don't know bad-MAP symptoms. ;)
Are there codes with a bad MAF?
Got a MAP in another vehicle you can swap places with?
Quick and easy compared with messing with injectors so it's worth a try?

Alvin in AZ
 
#6 ·
...I want include as much pertinent info as I can...
The caption of this diagram explains how to find ALL the relevant info, and put it in your profile/signature/avatar:

I can hear the fuel pump kick on when I turn the key on.
Great. Can you hear it turn OFF after ~1sec? Follow the first link in this caption:



And while the pump is running, what's the pressure?



The link in this one will find all the Haynes available on eBay right now; I recommend you get the last red cover, or the OLDEST blue cover:



If the truck still isn't running right after it arrives, get a digital multimeter (DMM; cheap is OK) and follow the ignition diagnostic procedure in Ch.5 (usually Sec.5 or 7). Regardless of anything else you do or find, read this caption & the NEXT few:

 
#8 ·
Also disconnect EGR or apply vacume to it. If its seal is broke it will sick in unmetered air.
I'd still suspect a bad fpr or injectors.
 
#12 ·
Steve83 - Heat Sink compound is used throughout the industry to improve the thermal transfer between the heat generating device and the heat dissipating device. You'll find it in your PC to transfer the heat from the CPU chip to the attached heat sink (and probably on your video card too). The factory used it on the ICM to heatsink interface. As long as the old dried up heat sink compound was removed from the heatsink, and applied thinly to the ICM and the heatsink, it will improve the heat transfer and the ICM will operate cooler than without the heat sink compound.

DC340 is used in the electronics community on transistor regulators, SCR and triac assemblies, large power diode heatsinks, etc. In my electronics career, I went through many tubes of it. You could get a lifetime supply here:
http://www.ebay.com/itm/DOW-CORNING-340-DC340-Silicone-Heat-Sink-Compound-350-F-/280620305862
 
#14 ·
My fav heat sink compound in engine bay is copper anti seize.
But great to hear updates.
As I recall wasn't there an issue with te dizzy mounted tfi catching on fire on some vehicles like t-birds and trucks.
 
#15 ·
Okay, so I finally got around to pulling codes today (jumper wire method), and I believe all I'm getting is a code 118 over and over.

"118 ECT sensor signal is greater than the Self-Test maximum of 4.6 volts."

Does that make sense? For it to just flash the same code a few times? I did warm it up before running the test.
 
#16 ·
I just took the truck out for a drive for the first time since driving it home over two months ago. It ran great! I just went about 10m down the road, then came back home and let it idle for 10-15m. No stalling! So it would appear, for the moment at least, that the TFI module was indeed the culprit.

So now I guess just need to figure out these codes. I actually took a video of the flashes with my phone, which I can post if necessary, but I watched it several times and I think it just keeps flashing 1-1-8.
 
#18 ·
I stopped by O'Reilly today on the way home from work and picked up a BWD ECT sensor. (I am really starting to like these Borg Warner lifetime warranty parts). Before installing the new sensor, I wanted to try and test the old one. I tested the connector and I had 4.62v. I tried to check resistance on the old sensor, but it was kind of a pain to do so until I removed it. With both tips at ~46 degrees F, the old sensor measured about 38k ohms, the new one was 48.8. So I installed the new one, put the coolant back in, and unhooked the battery for about 5m (I can never remember if this is necessary or not). When I started it back up, the CEL was gone.

We'll happens when I drive it tomorrow, but hopefully it's gone for good.
 
#19 ·
Cool, thanks for keeping us posted. I for one would rather learn by your
mistakes (experiences;) than to have to make 'em myself.

Ever'once in a while you'll read a really good long thread and the OP will
all of a sudden post- "I feel as tho this is a monologue". Hey, sometimes
the monologue is the best part. ;)

Your stuff sure as heck beats my dumb stuff, please keep it up! :)

Alvin in AZ
 
#20 ·
coolant temp sensor range should be measured in ohms, not volts. it sounds like it was bad, but just want to be clear for anyone else reading.
 
#22 ·
I did measure it in ohms, after checking for approximately 5v at the connector.
 
#26 ·
The two primary problems my truck had when I bought it (obvious problems) were the stalling when hot/won't restart/fuel smell, and the stalling when put into gear. I could be wrong (but i believe "diversity" was an old, old wooden ship that was used during the Civil War era?) ...but after the help I've received here, and some more experience working with it, I think it's safe to say that the TFI was causing the hot stalls, and the TPS the shifting problems. I've done a LOT of work to it so it's hard to say what exactly fixed what and all, but a properly functioning AND properly installed TPS is critical. I actually went to Home Depot and matched up some BOLTS for the TPS and tossed those stupid rounded Philips screws. This allows for TPS adjustment without removing it to tighten or loosen it.
 
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