help with hesitation problems

mcstein · Jan 5, 2011

Ok. I tried this on another forum with not much help. I have a 84 bronco II v6 2.8l 4x4 4spd. It hesitates usually when it's warm. It idles fine. It happens more when going up hills but it happens alot in cruise too. I live in a very small town so I rarely go above 40. I always let it warm up for 5-10 minutes and it'll drive fine for about 10 min before it starts acting up. No vaccum leaks. Timing is good and it advances (at least at idle). I gave it a tune up in oct when I bought it (dist cap/rotor, plugs/wires, fuel filter, oil and filter and air filter, new thermostat and flushed radiator). It also runs hot. usually right near the top of the N O R M range. I expect that that is a symptom of what ever is making it hesitate. I plan to do the dura spark conversion but that probably won't be for a month or 2 as I'm pretty low on the cash flow. Any ideas to fix this even if temporary?

Fuel pump going bad? TFI-IV module? I'm at a loss.

Thanks for any advice.

xr75er · Jan 5, 2011

if you have a code reader try to pull the codes first. But it probably your O2 sensor. It's about $40.00 at the parts store. it takes a 7/8 " wrench or a O2 socket.

mcstein · Jan 5, 2011

Thanks. I'll look into that.

unoleisu · Jan 6, 2011

Have you looked at the accelerator pump? 2.8 is carbed, and in the front there is a (usually) squarish plate that the carb accelerator linkage connects too. a little "arm" pushes into this squarish part. Inside that, there is a rubber diaghram that advances fuel into the carb when you step on the gas petal. When it gets old it gets stiff and cracks, (me too) and looses it's ability to work right. That usually starts out whith the symptoms you describe, and progressively gets worse, until complete failure....It should be like $5 or so.
I miss the good old days when we just had carbs to work on.....

Anyway, might look at that.

xr75er · Jan 6, 2011

unoleisu said:
Have you looked at the accelerator pump? 2.8 is carbed, and in the front there is a (usually) squarish plate that the carb accelerator linkage connects too. a little "arm" pushes into this squarish part. Inside that, there is a rubber diaghram that advances fuel into the carb when you step on the gas petal. When it gets old it gets stiff and cracks, (me too) and looses it's ability to work right. That usually starts out whith the symptoms you describe, and progressively gets worse, until complete failure....It should be like $5 or so.
I miss the good old days when we just had carbs to work on.....

Anyway, might look at that.

I guess i should have read a little closer.84's don't have an O2 sensor. I guess I was seeing an 86 or better. +1 to the accelerator pump.

mcstein · Jan 6, 2011

My truck had real bad problems misfiring in Oct. I took it to a mechanic who thought it was the accelerator pump flooding the engine. It turned out it was just out of time and he said the pump was good. It's not bucking like it did before but I assume the pump is still fine. I'll take a look at that though.

It turns out that I can't get any1 to scan my truck because none of the parts stores have a scanner that works for anything that old. Some of the shops I've called want like $85 to pull codes.

I can't afford to pay a mechanic to do anything and I'm at a loss.

Also it cranks a bit to start sometimes. 5-10 seconds. It was real bad before but I put a new starter in last week when the old 1 finally died. It always dies if I give it gas right after starting it and I usually have to rev it a bit so it doesn't stall when I try to drive without warming it up. (So I usually let it idle for 10 mins before driving)

feellnfroggy · Jan 6, 2011

Its possible that you have transmission issues not engine, does it do it when the engine warms up or when the transmission warms up.? But since it does it going up the hil and your checking the engine it could be a fuel problem. Doesnt a carb have a fuel bowl? it should be pressurize to prevent losing fuel during incline or decline right? So maybe start there.

mcstein · Jan 7, 2011

So I checked the accelerator pump. The diaphram looked fine. It wasn't dried out or cracked so I put it back but now it's now working. It doesn't squirt and of course once I get it started (I have to pour fuel into the carb) it dies as soon as I press the gas. After starting it a few times by adding fuel to the carb (which I never had to do before) I did manage to drive it about 1/4 mile before it died at the 1st stop sign.

Another wierd thing is I checked my timing again after talking about with someone. When I checked it before I never unpluged the single wire. It's supposed to be 10 before TDC with single wire unpluged. It was:

With wire plugged: 14 before TDC
With wire plugged with air filter housing off: about 35 TDC (I don't get this 1)
With wire unplugged near the 0.
I unplugged the wire with the air filter housing off while it was running and that killed the engine.

Why would the timing change whether or not the airfilter was on?

I guess I'll go replace the accelerator pump and start trying to fugure out the original problem again. I'm about to set this thing on fire.

unoleisu · Jan 8, 2011

The last time I replace an accelerator pump on my old 85 2.8 BII, the old one looked ok, but changing it out fixed the issue. I've had that happen on a couple of other older carbed fords. As a general rule I developed the habit (based on advice from this realy great old mechanic friend I used to know, who could tell you anything you wanted to know about every ford ever made from the model T, up to the 80's) that when it started to hesitate, change that first. I miss that old guy. He could on many occasions diagnose a vehicle from listen to it pull up to his shop. I think he was a wizard or something. He was allways right.

Sorry, I'm not sure about your timing issue, I haven't experienced that. I can't see it changing like that unless the distributer was loose... didn't happen to look at that, did you?

AaronC47 · Jan 8, 2011

Timing Issue ?

Its been awhile since I have had to work on a carburetor, It took me a few try to spell it right just now, ANYWAY, when I had performance issues I would start with a can of good carb cleaner, start the vehicle, gain access to the carb, rev it up and spray away all around the insides. Alot of times that did alot of good, sometimes no good at all.

The Timing,,, I was kind of confused when you said something about disconnecting a wire, ? I remember disconnecting and plugging the vacuum advance to set timing. If I am way out in left field here I apologize, I just maybe thinking a clarification may be needed.

Another thing to try, I found every now and then it seems that with gaskets and time and weather, the screws into the top of carb could use a bit of a snugging up, small minute pin holes sucking air.

Thats my thoughts on the issue. Good Luck with it.

I want to clarify, What "single wire" are you referring to when you mention unplugging it ?

mcstein · Jan 8, 2011

It'd be great if the accelerator pump fixed it. I don't understand why it stopped working altogether when I just pulled it off and put it back on. I checked the distributer for looseness by pulling off the rotor and cap trying to move it. Is there a different way? The wire was the vaccum advance. As far as air leaks near the screws, I'm assuming there aren't any because I tried cupping my hands over the intake on the carb to choke it off while idling. It didn't rev up. I think I read that on this site somewhere to test for vaccum leaks. We'll see what happens later today with the new accelerator pump.

kimcrwbr1 · Jan 16, 2011

You have to have all the sensors plugged in including the IAT on the air filter housing. The vacuum pod on the front of the carb controls the accelerator pump. Its the funny looking fitting with the 90 degree nipple out the front. disconnect it and plug the hose. Disconnect the battery for 30 minutes to reset the computer if you ran it without the IAT plugged in the computer will go goofy so reset it by taking the neg terminal off the battery for 30 minutes. Make sure all the vacuum hoses are connected properly and then run it at medium speeds for around 20 minutes to set the new values. You can pull the codes yourself with a volt meter or test light.

http://www.therangerstation.com/tech_library/OBD_I.html

This explains how or you can get a cheap code reader for EEC-IV OBD-1 either at the part store or online at ebay.

kimcrwbr1 · Jan 16, 2011

If you can do the duraspark now would be the time if resetting the computer dont work. I just got flashbacks on your description of symptoms and spent alot of money and time never getting it running right. The conversion only cost about $120 for the dizzy, cap adaptor ,cap, rotor and module. and you can eliminate 95% of the wires on the engine. But first try connecting all the sensors and vacuum hoses and reset the computer then see how she runs. you can try retarding the timing a couple degrees the damper pully gets old and lies disconnect the spout wire then start it let it get fully warm and set it at 8 degrees btdc. lock it down and plug the spout back in. If you messed with the idle air jets you will need to readjust them proper but start off with 3 to 3 1/2 turns out from lightly seated position I bet it runs pretty good there. Do not try and adjust the idle with the idle motor plugged in. the computer controls the idle. Set the timing at 8 degrees plug the spout in let the engine get warm and unplug the idle motor and then adjust the idle air screws for the highest lean vacuum or rpm. If yopu run it with the filter housing off the carb make sure you keep the intake air temp plugged in and all vacuum hoses either plugged in or plugged.

help with hesitation problems

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