I'm new here my truck is a 1990 f 150 larait extended cab 5.8L
E04D transmission. I've taken it to 4 mechanics and tried to solve problem of idle dropping way down and stalling when
Putting in reverse it low from park ??? It has new egr new idle control,plugs, distributor,Map sensor,pcv valve,throttle position sensor, water pump, caytilitic converter, throttle body removed and cleaned, rebuilt upgrade transmission, gas tanks cleaned out...... When I put it from park to reverse idle drops and it stalls unless I give it my foot on brake???? My 4th mechanic believes it's the harmonic balance don't think he's got it yet and avoiding me. Please help I've read all kinds of posts about same problem but no solution that works has been made in the past 5 years.

Thanks

 

Sounds like a problem with the ranger sensor on the side of the tranny. There are several iterations of this device that use different pin outs in the plug. Make sure yor connector is right for your range sensor. If tranny was swapped,or rebuilt it may have the wrong range sensor for the truck writing.

 

I don't see how the range sensor on the side of the transmission could do this. Maybe you could explain your logic? Or are you doing what the four mechanics did, just guess?

The ONLY way to diagnose this is to put a 0-350 PSI gauge in the test port on the driver's side of the transmission. You need to read the pressure with the shifter in each position from P to 1. Except in P and N you need these pressures with the truck standing still and your right foot on the floor. DO NOT HOLD IN GEAR AT WOT FOR MORE THAN 10 SECONDS. After each WOT pressure check fast idle in N for one minute.

 

The range sensor tells the pcm what gear the tranny is in. And the pcm does adjusts things like idle, timing. The pcm also decides when to tell the tranny to shift. So that is the reason to look at it as a suspect.

 

Sounds like your trans filter fell off or your fluid is low. Start with checking the level. If that's good, pull the pan and make sure the filter ain't laying on the bottom of the pan.

Checking line pressure as Mark said is a good idea as well and low fluid or a dropped filter would show as low pressure during the test.

 

Thanks I can use all the help I can get now! Just got back from mechanic harmonic balancer is changed but timing can't be set its leaking coolant at the top of
Water pump that was just replaced ? Near timing chain cover? It never ends lol! I am still curious why so many of
These trucks have this
Mystery stalling problem in reverse but no one ever finds the reason why? They just stop posting maybe they sell there fords and buy Chevy as an answer??? Just sayin😙

 

The transmission was rebuilt 3 weeks ago upgrades included by a qualified shop I would be surprised if it's still the transmission I would think for the price payed transmission is no the culprit, I will take it back if I ever get it on the road again

 

I've found the cause for several of these. It always boils down to low pressure.
That can be caused by low fluid level, a loose/damage/missing filter, leaking internal seals, a bad pump, or a defective torque converter. None of those can be ruled out because you paid a lot of money for a rebuild.

 

You need to find a new mechanic NOW!! How he ever thought the harmonic balancer would stall the truck is beyond me. What is his lame excuse for not being able to set the timing? And if it wasn't leaking coolant before you dropped it off, I'd suspect he messed something up and look everything over for evidence of such before bringing it up to him.

 

I'm at a loss for this truck ever running seems like everytime I have work done its run worst and worst? When I got the truck for $900 at least it ran would not stall in reverse now thousands of dollars later I can't even drive it. I'm no mechanic but seems like after 5 mechanics tinkering around and months later it would be drivable? I must admit the truck was much worse than I thought so many things had been Micky moused together. If this guy can't get it drivable, I
Might just park it and let it sit, I can't afford to even sell it for what i payed for new transmission rebuild!!!!!

 

I feel your pain. Too bad I couldn't even offer some suggestions.

 

I would take Marks advice and have someone test the pressure.

 

Is testing the pressure something a transmission shop does or a mechanic seems like all the mechanics I have run into wont touch tranny issues. Is this transmission testing 101 that should have been done before I paid 2,500 to have it rebuilt with upgrades whatever that means?

 

I don't know if you should have done it before or not. You (or someone) should do it now. It isn't hard to do. There is a plug on the driver's side of the trans. Take it out and thread a 0-350 PSI gauge in there. Read the pressures with the shifter in each position from P to 1.

 

Yes, always test things before condemning them. Looking at the part and saying "how can I prove this part/component is faulty?" before replacing/repairing it can save a lot of coin.

Most mechanics are line mechanics which means they replace things as assemblies. Most line mechs won't rebuild a transmission, rebuild a power steering pump, or put a set of gears in your axle. They just replace the entire thing instead. If you want it tested, go to a competent transmission shop (not AAMCO) and ask them to test your line pressure per Mark's instructions. If they won't do this for a small fee, then go elsewhere or do what I would do and just test it yourself. All you need is a pressure gauge and hose that can hold up to the maximum expexted pressure (300 PSI).