helping a friend here. 1989 f150 2 wh dr 302 speed density. bought the truck at sea level and moved to NM at 5280 give or take. drives to other places above 9000 ft and when doing so the truck shuts off. maybe sputters then dies. disconnect the battery and the engine will start again.

runs good otherwise.

no codes present. no cel. gave him the voltage values for the map and waiting to see what he says. don't know the ecu code.

any ideas.

 

Interesting, I hope you post the answer to this when you find it.

I would look at this from two angles. One possibility would be vapor locking but if it is running the normal fuel pressures I would think this would be unlikely. Second would be anything that makes it run too rich and especially if it was air pressure related, like the MAP.

Maybe someone with a diagnostic manual will look it up.

 

I am only guessing here. Could bad O2 Sensors cause this? It can be going bad and cause symptoms that do not throw a code. Since it is trying to adjust fuel to air, I would think altitude should effect them especially if they are failing.

 

The MAP sensor output is variable frequency, not voltage.



More information here: Fuel Injection Technical Library » Manifold Absolute Pressure Sensor (MAP)

 

Sensors don't "determine" anything the computer does that, the sensors either do what they are supposed to do or they don't and if that happens the computer(PCM) is programmed to ignore them and carry on using open loop tables... assuming the PCM is in good operating condition. And that is one of the more likely causes here, given the age of this truck a failing PCM wouldn't be surprising, these symptoms should produce codes too so if no codes at all can be retrieved.. not even the all clear codes then that too points at a failing PCM.
On the other hand the problem could be real basic, loss of fuel pressure, the TFI ignition modules had heat related failures that present in a couple different ways including stalling, or the truck could have other electrical gremlins elsewhere in the wiring.. a failing ignition switch could present the same symptoms as would corrosion on the PCM or fuel pump relay connectors. Lots of possibilities here.

 

Has it done this at 9000ft enough times to rule out it being a fluke?

 

yes this a ongoing issue. every time he drives above 9k ft. almost every time he has to disconnect the battery to get it to start. its happened enough he is asking what could be the prob.

have made the suggestion to put a fuel pressure gauge on it so it can be monitored. im waiting to hear if the all clear code comes up when checking codes. also trying to verify if the tfi has ever been a issue.

 

Just a shot in the dark, but there isn't a high altitude pcm is there? I know the map and o2 sensors should compensate, but maybe they can only go so far?

 

I read about the high altitude PCM and found it interesting. Since I don't know much about such stuff I didn't post it. I did look up the O2 sensors job and they merely report a lean or rich condition to the PCM and IT makes the adjustments. I still think they could be suspect but it's down the list.

I think it is vapor lock which can be caused by high altitude and an older worn vehicle. I read where Losing power gaining altitude and not being able to process the a rich condition can cause a vapor lock. At 9000 feet you have lost a huge percentage of your power and it's worse with an older motor. What I did also read is you can wrap the fuel lines with aluminum foil to help prevent vapor lock. I have no clue what it is or if the foil works. Just something for you pros to consider.

 

AFAIK there is no high altitude PCM calibration for these trucks, they should all run equally well at sea level or up in the mountains.. but the motor won't make as much power up there.

And vapor lock simply isn't possible with the return fuel system on these trucks, the pumps are constantly circulating a large volume of fuel between the tank and engine so there is nowhere for an air/vapor pocket to develop. That assumes a fuel system in good running order however, on this truck there is the added complexity of a dual stage pump system with low pressure pumps in the tanks and a high pressure pump on the frame so there is more potential for fuel delivery issues than there would be with a later truck.

 

I have seen altitude compensation on other vehicles. Seems like there was a vent on a computer in one that had to be clear to work. Also seems like I saw a switch for altitude compensation that I thought was for a Ford. Still none of this directly is related to dying at altitude.

I have driven over 13,000 ft in Jeeps. I think we got close to 14,000.

My old 1979 F250 didn't like altitude and vapor locked.

 

I'm at work so I only have a few minutes to look but found a high altitude EEC for a 86... Don't know if they continued on in later years or not.

https://www.partrequest.com/auto-parts-detail/86-ford-bronco-engine-ecm-elec-cont-unit-ecu-8-302-5-0l-at-high-altitude-66247-281690170479

​​​​​​​also if its worn out, at 9000 ft you are down like 30% on air. I bet there's barely enough compression to fire it off. May need to advance timing too.

 

I think the situation is that High altitude emission Systems is what makers put in their vehicles. There is a Cordone rebuilt PCM that is programmed for High Altitude Emissions and I assume the vehicles made with the HA emissions had their PCM's programmed for it. So one doesn't work without the other.

I only think that this could be how it goes.
So if he is running stock and is at 6,000 feet and it still runs without dying and the higher he goes and the leaner he gets and motor is working hard, it finally dies at 9K ft. I think the two conditions could cause the dying. Tremendous motor strain causing overheating and power loss and the lack of air to fuel. PCM maxed out on performance in some area that will correct itself by disconnecting the battery or waiting a few minutes (time). Whatever that component is, is the root.

 

thanks for all the input. the last one holds water in my thoughts.

well see what we can come up with this wknd. ive lived at 6000 ft or higher most of my life so 9000 ft is really nothing to us here. the truck is in good condition afaik. well see.