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Discussion Starter #1
Alright guys, I need some help. Here's the story: I live in Ohio, on the 3rd we traveled to the Harrisonburg VA area for a family reunion. On the way back that night, the Taurus we were in blew the front main transmission seal. So we got a ride back to Ohio. Early morning on the 5th, we headed back in my Bronco to pull the taurus home. We got there fine, truck performed great. Wasn't the fastest up the mountains, but I was purposefully making this a nice, relaxed drive. We get to Harrisonburg and pick up the trailer, then the car. All is well. We then fill up for the ride home. Soon after this, as I am driving through town, the truck begins to stall at every stop light. Any time I let off the accelerator and slow to around 5 MPH the engine stalls. I can restart it easy enough, and if I give it a slight amount of gas at a light it will remain on. If I let off the fuel, it starts to stammer. It sounds as if it has a huge cam for a moment, then dies. I was fine with this because anytime I am on the throttle the engine runs normally. I proceed onto the interstate and all is well. It is maintaining highway speeds without any trouble and the temperature gauge sat on the 'N' of Normal.

Next thing I know, it starts to sputter and feel week. It then proceeded to stall, exactly how it did when I ran out of fuel a few weeks ago, lol. I immediately suspect the fuel system, as I know I have almost a full tank of gas. My first assumption is a faulty fuel pump. I proceed to check the fuel pressure check valve. To my surprise, it has a lot of pressure, bu all that comes out is vapor. There is very little liquid gasoline. Now assuming the problem is a vapor lock due to the hot weather and the load, I opt to wait a little while on the side of the road for it to cool. Lone and behold, not ten minutes later, a tractor trailer sideswipes my rig, crushing the left-side wheel assembly of the trailer, leaving a dent while taking the mirror from the car in tow, and really messing up the drivers side of my truck. It made a huge dent in the quarter panel, an even larger one in the door, tore off the mirror and the swivel window, and destroyed both hubcaps. The impact put the truck in 4x4 and knocked the dash apart while blowing the flasher fuse and turning on the running lights.

Lone and behold, the beast still runs. I unhitch it from the trailer, and when all else is towed away, we drive the truck into town. So it cooled down and is no longer vapor locked. It drives just fine from what I can tell, all except for it stalling out when I slow to a stop. I'm beating my head against the wall trying to figure this out. Ive never had this thing leave me stranded anywhere, I'd be sad to have it start now. My initial thoughts were bad gas, since it happened right after a fill. But it runs fine when I'm actually driving and not just idling. I put in a bottle of heet and topped it of with about 10 gallons of premium fuel, no change. So I'm starting to stray from that theory. Also, ever since this stumbling sarted, it has smelled like it is burning extremely rich, like I can see dark colored exhaust and when sitting in the truck, the exhaust makes my eyes burn. This reminded me of the effects of a bad coolant temperature sensor on another car, it burned way rich and wouldn't idle at all when warm. So I replaced it. No change. Now there appears to be a second CTS in the intake manifold, I changed the one above the water pump and beside the distributor. I can try changing the other tomorrow.

I appologize for the length of this and I appreciate any suggestions you guys may have. I'm going to sleep for a few hours now, but I'll check back first thing in the morning. Thanks again!
 

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Discussion Starter #3
Forgot to mention that it is a near bone stock 86 FS Bronco with the 302 and AOD. The engine is out of an 88 F150 but all the electronics are original from the 86. It was a factory 302 and the motor blew before I got it, so I go it cheap. It has a rather large radiator, don't know what make or model, it was there when I got the truck, I put in a 160 deg thermostat when I put the new motor in two years ago. I also installed an axillary transmission cooler. Don't know if all this stuff matters, but if it helps, here it is.
 

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Discussion Starter #4
I don't have any codes. I know there is a thread on here that shows how to check, but I haven't got a chance yet. I can get that up tomorrow. There is a vacuum leak under the dash. It has always been there though and doesn't sound like it got any worse. Would that be worth plugging?
 

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House of Windsor 4ever!
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You didn't list what year, engine, etc., so I'll have to be a little more general, but check the following: MAP or MAF, whichever is applicable; air charge temp sensor, in one of the lower manifold runners (may be the second one you're talking about); oxygen sensor (upstream one if OBD II, on '95 and '96 Broncos) harness, as if it is shorted to ground, the computer will enrichen the A/F mixture.
 

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Chillin on the Gulf Coast
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I hope no one was hurt in the wreck and that the 18 wheeler stopped and all that is well. But as far as your idling issue, you may want to take off the idle air controller and give it a good cleaning. Also you may want to check a price and see if its worth your money to try swapping it and clean and keep the old one as a spare.
 

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House of Windsor 4ever!
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The 160* thermostat is a huge mistake, as the computer will only see a low temperature and enrichen the mixture accordingly. EFI requires a 195* t-stat everytime, all the time. The load you put on the truck started taxing the engine which was barely making any power due to the rich run condition, and wasn't hardly able to pull the trailer and car. Did the trucker get caught and shut down?
 

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House of Windsor 4ever!
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I don't have any codes. I know there is a thread on here that shows how to check, but I haven't got a chance yet. I can get that up tomorrow. There is a vacuum leak under the dash. It has always been there though and doesn't sound like it got any worse. Would that be worth plugging?
That vacuum controls your HVAC motors for where air comes out at.
 

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Satyr of the Midwest
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Pull codes. Click here: http://www.fordfuelinjection.com/?p=13

You're lucky you didn't set yourself on fire, letting fuel out of the Schrader valve like that on a hot engine. That IS NOT how you test fuel pressure; only a gauge can tell you whether it's correct. There's no way to differentiate between 20 and 40 psig, and only one will allow the engine to run.

ANY vacuum leak on an engine is bad. Cap it off accordingly temporarily, repair as required when time allows.

Try pulling the vacuum line off of your fuel pressure regulator. If it smells of fuel at the end, or fuel drips out the line, then it's likely your fuel pressure regulator's diaphragm is ruptured and needs to be replaced. While you're up there, check around for other vacuum leaks throughout the harness. Make sure that reservoir on the fender isn't leaking, either.

If the regulator is good, I would start looking at the ignition system as a possible trouble source. The diagnostic procedures are in the Haynes manual, but have a look at the sections regarding ignition module, coil, and spark plug wire testing.

The 160° thermostat was a BAD mistake. Replace it with a 195° thermostat as soon as possible, preferably NOT an AutoZone/Hecho en Mexico part that will fail. Make sure you're using a 50/50 mix of clean tap water and antifreeze in the cooling system, and that the radiator cap is fully functional (verify the system is holding pressure when hot).

EDIT: Vapor lock DOES NOT HAPPEN in our fuel injection systems. It's pressurized in the tank for that very reason, and there's no way for fuel under pressure (at least around 30-40psig) to vapor lock.
 

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I had very similar symptoms in my 1990. Ended up being solved by replacing the fuel pump as well as the fuel pump relay. I thoroughly believed it was vapor lock but ended up changing the fuel pump out of frustration. Turns out it was the correct thing to do.
 

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Discussion Starter #11
Thanks for all the reply's guys. I will swap out the thermostat as soon as I get home, and I'll seal that vacuum leak today. The trucker did stop and the state police came and filed a report and ticketed him accordingly.

I realize letting fuel out on a hot engine is definitely not the brightest idea. I just didn't think to bring my pressure gauge with me and was doing my best to troubleshoot on the side of the highway:banghead. At least I had my fire extinguisher sitting right beside me.

The coolant is a 50/50 mix and was changed about a month ago. I'll also check the fuel pressure regulators vacuum line to see if it smells of gas. I was convinced vapor lock couldn't happen on EFI engines as well, but why else would there be so much vapor in the fuel rails? Do you guys know of any store to get an inexpensive fuel pressure gauge? I already tried the local advance auto. Obviously I am not the authority on these engines, but if it was a bad fuel pump, wouldn't it run best at idle when fuel demands are low, and worse when fuel demands were increased? If it is the pump, is there just the fuel pump mounted in the frame rail? Or is there a lift pump in the tank as well? Thanks.
 

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Discussion Starter #14
I have to keep my foot on the gas. If I'm just barely giving it gas it will remain running, but run very rough. If I give it a lot it will rev out and appear to run normally, aside from the bad smell of rich exhaust.
 

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penis
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O.K think we have it narrowed downed I really doubt it is your fuel pump so thats good I would go with a vac leak first, the test the collant temp sensor, If you need on I should have one I can send you, or the air temp sensor
 

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Satyr of the Midwest
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O.K think we have it narrowed downed I really doubt it is your fuel pump so thats good I would go with a vac leak first, the test the collant temp sensor, If you need on I should have one I can send you, or the air temp sensor
It doesn't narrow down anything without knowing the condition of the ignition system.
 

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shibby
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I'm wondering if it's a bad fuel pressure regulator. When you're applying throttle, you're increasing the amount of air in the system which helps cancel out the excessive fuel.
 

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also in 86 they did have the fuel system hooked though the oil pressure sensor on mine i would get an erratic idle that was caused by the oil pressure sensor. also if you are getting a rich runing condition check the MAP sesor i do believe the 86 fi had one (could be wrong though it was a while ago AZ has a listing for one)
 

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Discussion Starter #19
Just tried to get codes. I shorted the STI wire to ground. The emissions light works, as it comes on for bulb check every time. I heard a few extra relays when I turned the key on, but aside from the normal bulb check, the emissions light doesn't flash at all. I'm going to try the multimeter method now.

I just started it for the first time after it was 100% cooled down. It idled almost normal, just barely rough. The exhaust is still visibly dark though and smelled very rich. My guess is the same problem, but the rich mixture works to some extent now that the engine is cold. I'll keep checking stuff. Thanks for the input everyone.
 

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Discussion Starter #20
I got information from the multimeter test. I'll post up the codes in a minute and probably the sound recording in case you gents want to double check my counting, lol.

As for the fuel pressure regulator, the vacuum line did smell like gas. It smelled of it even stronger after I started the truck and revved it up a little. Is there any conclusive test to show that component good or bad? I disconnected and plugged its vacuum line, then started the truck and it ran almost identically to how it did with the vacuum line connected. I don't know if this proves anything or not, but let me know what you think.
 
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