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Old 12-07-2008, 04:58 PM   #1
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Default 1995 F150 power loss upon acceleration

Hello, all! I appended this question to an abandoned thread earlier, but no luck..

Last night my truck ran just fine until suddenly a condition occurred on the highway, leaving me coasting while feathering the throttle to keep the engine going..

I have a 1995 F150, 5.0l, auto. and now I can't even reach speeds of over 5-10 km/h - while it backfires and gives that nice, powerless throaty sound, but has NO power!

No load: engine runs ok / only Intermittently stumbles & shakes
Under load: Engine stumbles almost to stalling, must feather the throttle to keep a steady 5km/h..

-Strong smell of fuel, so we know the fuel pumps are ok - changed fuel filter anyway,
-Changed cap & rotor, plugs were fouled but no improvement with replacement,
-Re-checked my plug wires to assure correct firing order...
Smashed the EGR with a hammer a few times to see if it was stuck open - nothing
-Going to pull the throttle body off next & clean / test the IAC solenoid...

The EEC-IV gave me 3 interesting codes:

172 HO2S system indicated LEAN condition (our biggest clue) - continuos
334 EGR valve pos. sensor out of expected voltage range (high) - off, running
538 ??! What the heck does THIS mean? - off, continuous

The condition occurs intermittently (AFTER I think it's ok to take a drive,) but is at the point now that it's not at all drivable -- there was nothing wrong otherwise before this happened...

PLEASE HELP - I gotta get to work somehow!
Thank you!

Last edited by Rickter_scale; 12-08-2008 at 04:37 PM. Reason: typo
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Old 12-07-2008, 06:27 PM   #2
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Sounds like the EGR may be sticking open, causing the computer to think the truck is running lean. Inspect the whole EGR system, the position sensor, the EGR valve and the EGR soleniod. I'd also check the TPS for proper function and adjustment. 538 means you did something wrong during the engine running test.
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Old 12-08-2008, 03:12 PM   #3
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Thank you for the quick response!

Alas, here are my findings:
EGR Solenoid - vents properly to atmosphere upon energization
TPS - 3.9k ohms to 390 ohms when bottomed out (plus, it's been changed not 9 months ago)
EGR pos. Sensor - 3.9 k ohms retracted, 390 ohms bottomed-out (has been changed, again, not 9 months ago)
EGR Valve - stalls idling engine when vacuum present...

All seems fine in regards to the EGR system -- Out of frustration, I fashioned an EGR block-off plate, to no improvement...

Further help please: I'm at a loss!
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Old 12-08-2008, 08:24 PM   #4
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Well 334 means EGR closed voltage higher than expected, which means either the EGR isn't closing all the way or the sensor isn't positioned right giving the computer a higher reading than expected. If the computer thinks the EGR is stuck open it will remove vacuum from it to try to close it.
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Old 12-09-2008, 10:56 AM   #5
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I totally agree with you on this code, EXCEPT, I've been receiving such a code for 2 years now and the truck ran just fine up until 3 nights ago.. I just put the throttle body back on after cleaning it up somewhat, but I highly doubt that replacing the EGRV will perform the miracle we're looking for..

Today I'll test the actual fuel pressure, then consider setting it alight and renting a vehicle or entrust it to a (gulp) mechanic... (which I am TOTALLY against)

Thank you - I'll get back with further findings..
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Old 12-12-2008, 06:48 PM   #6
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Hey again..

I've had time to brainstorm the issue - since it now, will not happily start.
The 'symptomatic' problems (DTCs) have existed since I've owned the truck (2 years,) I was hoping that you may agree with me that the problem COULD be, indeed, the in-tank fuel pump.

Can anyone else with the same issue I've read on here tell me how they resolved their OWN issue of the SAME problem as I? Most of the threads / questions on the "power-loss woes" just end, with no return input or Thanks!

So, agreed? Fuel pump? Trying to get an adapter for the Schroeder valve for a pressure gauge, but it doesn't exactly 'soak' me with fuel spray when I press it down... Is it supposed to be around 35-45 psi?

Hilfe mich, bitte!
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Old 12-13-2008, 04:48 AM   #7
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Definitely check the fuel pressure, then you can decide if the pump is at fault. 35-45 PSI is good. See if the pressure bleeds down when the pump stops running, It may some but shouldn't do it fast. If the problems started after messing with the throttle body then the problem probably lies there. Check the adjustment of the TPS, at the idle stop it should be just under 1 volt.
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Old 12-13-2008, 10:36 AM   #8
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The is very little volume with the pumps off. The pressure may be ok but because the fuel does not compress without the pumps running there will be just a little squirt of fuel coming from the Schroeder valve. Try this test while someone else turns on the ignition or cranks over the vehicle.
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Old 12-13-2008, 02:34 PM   #9
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Thank you very much, Gentlemen.

Nah, I just cleaned the throttle body - reading took me to peoples' ports being blocked solid, but I changed out the TPS last year (which is UNDER the TB - funny!) and figured I'd install the gasket this time...

Definitely no fuel pressure - gonna beat the tank to see if I can't kick-start it or knock some crud loose from the strainer. But it's -15oC here today -- in the daytime -- need some encouragement, or just courage!

In the summer, I added a high-pressure fuel pump (from my 1990 F150) 'cos it was acting up then - I figured it would totally eliminate ANY fuel pres. problems...

Ford Canada wants $300 for a special-order pump (?!) and $50 for their upgraded wiring harness... What a f.. JOKE.
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Old 12-15-2008, 07:10 PM   #10
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yea ive been having power loss problems on my 87 f150 300 6. my automotive teacher told me the MAP sensor might be gettin insuffitient vaccum(all the ports are takin) but idki bought e reman computer and my computer has been throwing the infamous 334 code also. the thing that gets me is that when the truck is first started it dosent runn good at all stumbling and shaking and hesitating upon reving. but once it warms up correctly it runs fine. it also has a gas fume smell while idleing as rickter said. any help would be awesome
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Old 12-15-2008, 07:10 PM
 
 
 
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