Running Issue
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4wd Low
Joined: Jun 2024
Posts: 11
Likes: 1
Running Issue
Hi all,
New to this forum, I am hoping someone out there has dealt with the issue I am having.
I have just bought an 86 F100 ex Ambulance, 302 EFI, runs really well for 20-30 minutes, then starts coughing and loses power.
I have replaced spark plugs, Distributor's rotor button and rear fuel filter.
The truck has dual tanks, the problem exists regardless of which tank is being used so I am assuming the problem is somewhere between the high pressure pump and the engine.. There also seems to be air in the fuel rail. I am thinking that if it was the injectors the problem would be there from start up?
Any feedback/thoughts greatly appreciated
New to this forum, I am hoping someone out there has dealt with the issue I am having.
I have just bought an 86 F100 ex Ambulance, 302 EFI, runs really well for 20-30 minutes, then starts coughing and loses power.
I have replaced spark plugs, Distributor's rotor button and rear fuel filter.
The truck has dual tanks, the problem exists regardless of which tank is being used so I am assuming the problem is somewhere between the high pressure pump and the engine.. There also seems to be air in the fuel rail. I am thinking that if it was the injectors the problem would be there from start up?
Any feedback/thoughts greatly appreciated
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
You need to check fuel pressure with engine running long enough to reproduce the problem, I suspect you have a failing pump. The fuel delivery system in these trucks normally pushes more fuel than the motor can ever use so there is always some going back to the tank and there should never be air in the lines. The fuel system is complicated however with a frame mounted high pressure pump, in tank low pressure pumps, a resovoir/switching valve on the frame that manages flow to and from the tanks, and a frame mouned filter. There should be 32-35psi pressure at the rail with the engine idling and upwards of 40-45psi with vacuum removed from the fuel pressure regulator, pressure should never drop below the 32-35psi level.
Thread Starter
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4wd Low
Joined: Jun 2024
Posts: 11
Likes: 1
Thanks Conanski,
The pump does look quite old, possibly the original! I'm guessing air in the fuel rail could only be the HP pump or a leaky fuel line. Given the is no leaking fuel the pump is probably the most likely.
Think I'll just shell out for a replacement.
The pump does look quite old, possibly the original! I'm guessing air in the fuel rail could only be the HP pump or a leaky fuel line. Given the is no leaking fuel the pump is probably the most likely.
Think I'll just shell out for a replacement.
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