help ive been working on my sons 1986 bronco for a month . started with a compresson test 125 -130# did a tune up k&n filter new flow master, weve changed every sensor that weve been coded. all but knock sensor,collant temp,and egr it was changed just before we bought the truck. last week installed computer #2 its running good now, still missing occaisonaly,still dies at stop signs now and then when warm.my latest code is a 44 thermactor air sys. failure. INDICATES THERE IS A PROBLEM? no s---! i say . can any one help me , or should i part it out on ebay and buy a blazer.
chet.

 

It sounds like the air diverter valve may have failed....

use the haynes manual to troubleshoot the air pump system

you should have the air pump (it should turn without much effort and no play on the pulley)

the air diverter valve that gets the air being pumped from the air pump
and diverts it to the cat converter via a smaller down tube before the converter on exh pipe.

If it misses then your check valves may be bad....these are mounted closer to the exhaust manifolds...and are not supposed to allow air out from the exh manifolds...but are supposed to let air in from the air pump to warm the truck up.

I would replace both check valves AND diverter valve and get back to us...
Also check the vacuum lines going to the diverter valve.

cheers
R

 

A couple possibilites...

1. Your catalitic converter is clogged: These will quickly clog up if your thermactor system is inoperable or if too much fuel is being shoved through your engine. Your symptoms are almost excactly what my ol 88 cougar experianced when it's 3 cats went bye-bye.

2. Fuel pressure regulator and/or fuel injector failure: If your fuel pressure regulator fails and either cuts off the fuel supply to your injectors or overpressures them they can and will fail. Case in point; about a year ago I noticed my truck running a little rich figuring it to be just a bad O2 sensor I ignored it, then about 6 months ago when the temp out here started to warm up and so did my engine I started losing a cylinder. Figuring it was just a weak spark due to a failing alternator I replaced the alt. The problem went away for a little bit but then returned and got progressively worse till it was missing all of the time. For a good month I tried to trace down the cause of the miss but to no avil. to cut a long story short a couple of weeks ago I replaced my injectors with some take outs from Five-O Motorsports and my missing problem was resolved. Apparently the regulator failed causing an overpressure of my injectors causing one or two of them to pop.

 

Sounds like your TAB and/or TAD solenoid(s).

The thermactor bypass and diverter valves are actuated by small solenoids called TAB (thermactor-air-bypass) and TAD (thermactor-air-diverter) valves. The computer tells the solenoids to open/close, and the solenoids in turn direct vacuum to the the actual diverter and bypass valves.

The TAB and TAD solenoids are prone to failure and when they do fail the problem can be difficult to diagnose. However, the symptoms are:

1) stalling after you come to a stop.
2) "lean" code
3) "EVP outside of tolerance" code
4) rough idle

I think I paid about $45 each for the two solenoids. Also replaced the one for the EGR valve -- it checked good, but looked identical so I figured it would probably go next.

 

the air pump is working, check and rear pipe new, diverter good.cat is ok, ive replaced all vaccume lines from reservoir to there prospective places, while running the lines i noticed the switches tad&tab had been un pluged & filled full of grease i cleaned them,the guy i bought this from was a electronic engineer from boeing, must have got the grease from there, i dont think it was supposed to be used on low voltage, or it was just ep2 and it got old! i removed the injectors cleaned, tested, and replaced the o rings. now test says o2 running rich im changing fuel reg now

 

I've been plagued with the same problem on my 86 f150 5.0efi...code 44r. Ford does not make the TAB and TAD any more. I got some from a junk yard. Still code 44r. Checked vacum at Air bypass and diverter units...they were working. System is working but shuts down too soon, like when truck warms up from extended idle like it's supposed to. Replace temp sender unit, no change. This is causing a high HC emissions because the air pump bypasses too soon and starts dumping air. I've replaced all senors except egr and fuel regulator. I'm thinking I have a small vacum leak at the egr and it's causing the vacum to shut off too soon at the air bypass valve. Nobody on this site has been any help. If you find the problem come back to this site and post your fix, as I will do the same.

 

ive changed the pressure regulator. still missing! if this was an older rig i would say the points are fried. re tested, says 18 loss of ignition in memory,maybe because it died ? 41 no exahust gas switching detected - lean. and knock sensor#25 i missed the goose test. my parts pro is researching my computer to make sure i got the right one. it ran so good after i put the new one in but 2 hours later when my son got in it ran like crap.i think im running in circles. any ideas?

 

o yes idling in drive you turn the steering wheel and it sometimes dies.

 

What motor do you have? Fuel injected?

 

5.0 injected. Replacing knock sensor now.

 

have you check the voltage at the TPS? I'm asuming you did and the timing ..10BTDC. Maybe you got a worn distributer. Doesn't make sense you getting different codes all the time. I'm just getting one code 44r. And I'm stuck on it.

 

I also get the code 44r, and it also says running rich, whitch i belive because the mpg's suck. so if you figure it out let me know too.

 

had a ace mechanic tell me my fuel pump was bad! 44 lbs looks good to me. i can hear the check valve on my air pump switch during warm up. im lost! freeking ford! its beautiful, black on greay centerlines with 33" ta's but runs like a vega. i would say it had bad points if i didnt know better, oh for the good old days.I just bought the hand book EEC IV from dali designhttp://www.dalidesign.com/hbook/hb6.html we will see if it helps!

 

Sorry, but I'm still suspicious of the TAB and TAD solenoids. When mine failed, they caused a vacuum leak. Some vacuum was going where it was supposed to, but the rest was just leaking. Your situation just sounds too familiar to mine.

The best way I found to troubleshoot this stuff was to use one of those hand-held vacuum pumps -- I think it is called a "Mitey-vac". I put a vac gauge on it and then attached it to the various components under the hood and pumped them up one at a time. If the vacuum held, I moved on. It was time-consuming, but I can't think of any other way to pin-ponit the problem.

 

Since it's running rough and fails to idle, have you checked ignition parts and idle air control (IAC) valve? A failed-closed IAC valve would cause stalling at idle. However it would not affect performance above idle.

Make sure all spark plug wires are routed correctly and don't "crossfire".

Were all compressions reasonably close and measured warm?

I'm struggling w/ a 90 Bronco 5.0 that is very similar to yours. It runs OK under light throttle and idles fine, but "sags" and lightly backfires through the TBI under heavy throttle. Retarding timing setting helps a little, but doesn't totally fix. I'm somewhat like you,...frustrated.

good luck