Once the truck gets to operating temperature it hesitates and sometimes stalls, the stalling happens mostly in reverse and it only happens in drive if you hit a certain spot in the gas pedal when taking off. The truck starts right back up every time. Once you get past the little hesitation she is smooth as silk. The TPS is new, the IAC valve is new and the MAF sensor is new. The temperature gauge doesn't work the switch might be bad but I think the truck would run like crap all the time if that were the case... It's easy on gas, It doesn't smoke at all, great acceleration, it's just that one spot as soon as I put the weight of my foot on the gas pedal. It's all I've got to drive so I've gotten pretty good a missing that spot, but driving it is only going to make things worse. I read in another forum that the transmission fluid/filter could have something to do with it (something about the filter falling off and laying in the pan?). I know my way around these trucks pretty well and this is the only one of the 12 I have owned that stumped me and im losing sleep over it any input or advice would be greatly appreciated!

 

First question, is the check engine light on, or has it flashed in the past other than at first start?

Have you checked codes?

 

No check engine light and i haven't checked the codes, i dont know anyone who can check obd1 i forgot to mention in the post that the belt is off of the smog pump. I don't think thats the problem as I've never had one that had the smog pump hooked up.

 

Here is how you can check your codes
https://www.fordtruckzone.com/threads/how-to-check-codes-on-obd1-and-2-without-a-scanner.654744/

Smog pump comes on at above idle, and goes off at full throttle
It has no effect at idle

I am assuming your truck is EFI, not carbureted

 

Opps
forgot
codes are here
https://www.fordtruckzone.com/threads/obdi-trouble-codes.659342/

 

My

 

I tried to check the codes, but my test light is a piece of crap. It didn't work. I'm going to get a good one tomorrow. I also noticed my truck has an emissions light that turns on when I turn the key on but no check engine light and i dont see a place in the instrument cluster for it. I looked at my 85 4wd, same thing. And I'm 99% sure the 84 2wd and the 84 full-size bronco I had was the same way. None of them had a working smog pump and the light didn't stay on in any of them. You're right it is EFI I forgot to include that, but if i dont figure something out soon it will have a carburetor on it. I don't want to go that route through. What's it take to do away with all of that smog stuff? I've never done one but whoever did my 85 before i got it just cut and plugged all the lines to the egr and pulled the pump off. the piece on the back of the heads is still there. I'll just leave it there if I can't get rid of it all.

 

85-89 is all the same efi on the 5,0, just wanted to make sure no one changed it yet

In 86 it will say emissions, not check engine, that's the last year for that. Honestly, you will have less problems from the efi than the carb, there is a lot to change to go back.

Usually if there are no hard codes the light stays off, so you are probably there anyway.
More than likely you have a vacuum problem. probable a line, ir a gasket.
The throttle body gasket is sometimes an issue, that's the first gasket you come to between the throttlebody and the plenum.
They dry out, and allow air to penetrate

Vacuum on your truck is in 4 stages. Black is main , red is reserve, white usually goes for the heat/A/C. green to EGR
Then there is a vacuum can for reserve on the passenger fender, looks like a coffee can, usually rusts out.
on the driver's side under the reserve tank is another for cruise control, that one rusts out too.
pay close attention to the lines where they go around the back of the plenum, they crack there.

Not sure which transmission you have, the c6 has a modal on the back that has a vacuum line that cracks. It will cause shifting issues too.
AOD uses a cable to the throttle body to shift. E40d uses the computer and TPS

I'd start with throttle body gasket. then go from there.

 

The guy that had the truck before me changed the TPS, he isn't to bright he probably put the old gasket back on the truck. I'm going to try to check the codes when I get off work and see where that leads me I'll let you know as soon as I know

 

Tps requires an adjustment, that could very well be your problem

 

How do you adjust it?

 

I'm pretty sure it's the aod, I didn't pay much attention to it other than the pan is stamped metric, my 85 has an aod and it's got the same pan. I didn't have time to check the codes tonight but I'm going to get up early in the morning and see what I can figure out. I got to my truck after work started it up and let it warm up I came back to it about 20 minutes later it was idling fine as usual I drove off came to a stop sign about 5 minutes up the road and it was idling a little rough, it didn't do it any other to.e I stopped. I've never had the truck much above 45 and never ran it in overdrive till this evening, it started hesitating once I got to 60 mph and kept the pedal in one place it would smooth out if I let off of it a little or got into it a little. I've never noticed that when I run in drive, but I'm usually on back roads and the pedal doesn't stay in one spot. I got a multimeter and a good test light this evening I'm going to try to test everything in the morning. It's all I have that's really "road worthy". My 85 has 375,xxx very hard miles on it. I need to get this thing fixed before this stupid problem creates a big problem and I'm walking...

 

I figured out how to adjust the tps, it was reading .72 volts, I got it adjusted to .91 volts, tested it with the multimeter and it has no flat spots. No more hesitation! But, now it surges a little when it idles and when im going down the rd and I go let off the gas to turn the once the RPM s get down to idle speed the engine shuts off, but it cranks right back up and idles fine till it starts surging.

 

Now it will idle at about 1300 or 500 RPM and when i come to a stop it will surge between the those 2 or 3 times then stall, my boss left the job so i went to my truck and tried to check codes with new test light, it didn't work. The MAP sensor isn't new on this truck like I said in the original post the guy i bought it from told me he replaced it, I'm going to pull tgr one off my 85 and try that

 

Map will do that. Make sure the vacuum line to the map sensor is plugged in on both ends
Sounds like you have a vacuum leak too. check that reserve can on the fender, I bet it has a hole or two in it.


Aod transmission has a cable like the throttle cable hooked up to the throttle body. if AOD, you have throttle cable, cruise control cable and the transmission cable