300 i6 engine is sputtering and stalling only when hot?

MACK TOMYN

MEMBER
1990 FORD F-150
4.9L
6 CYL
4WD
MANUAL
181,000 MILES

I've checked codes and received: 41/Lean and 95/Fuel Pump issue.
I've replaced both fuel pumps, both tanks are brand new, I beefed up the wiring & made another ground for the pump, traced all of the wiring 100%, replaced the fuel pump relays.
The issue persists with the front and rear fuel tanks so-
I've replaced all the spark plugs and lead wires, the ICM is new from Motorcraft.

It initially takes about 20 minutes for the truck to warm up and start sputtering until it sounds like it's suffocating for fuel, I can flick the key off and back on instantly while coasting and it runs great again for only a few minutes until it starts to chug and buck again.
I put my fuel pressure gauge through the dash to watch it while driving and it's not lacking fuel pressure but sure feels like it is when it's warm. Could this be my ignition coil? Or vacuum return to the tank maybe?

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi,

Do the same codes return if they are cleared? Also, code 95 indicates an open circuit to the fuel pump. However, if the fuel pressure remains consistent, that doesn't make sense. See pic 1.

Code 41 could indicate a lean mixture, or the sensor is not responding. Have you also replaced or inspected the HEGO sensor? See pic 2

Let me know. Also, let me know if there are any exhaust leaks pre-catalytic converter.

Take care,

Joe

See pics below.

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Thursday, November 17th, 2022 AT 5:56 PM

MACK TOMYN

MEMBER
2 POSTS

Fixed! (But I have a new issue) The injectors were terribly clogged, and my fuel pump socks were clogged- the seal on my tank started to leak, so I took the complete set of injectors out of a parts truck which have a totally different part number. My old ones had one single needle in the middle E65E-B4B, the newer ones have 4 holes and no needle but it definitely has more power now and runs great (when my map is unplugged).
There are no codes or check engine light when my MAP is plugged in but my idle doesn't drop for a few seconds after letting off the gas, and I have less power with the MAP plugged in.
I basically can't shift without potentially hurting my clutch when the map's plugged in because of the high revving and throttle sticking. When it's unplugged it runs perfectly except when it starts idling (loping) like it has a cam, and of course the annoying check engine light pops up when the map's unplugged.
This problem occurred before changing the injectors, when I was replacing the sensors and came across taking the TPS off and put it back on, I started it up for a test and it started revving so high while cold I had to kill it right away. There are no vacuum leaks, I resealed my intake manifold and every gasket on the motor is new too.

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Monday, November 28th, 2022 AT 7:34 AM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi,

It is likely because the injectors are providing a different amount of fuel. The idea that it runs better with the MAP disconnected is because the engine goes into a predetermined setting. When it's connected, the system isn't making sense of the amount of fuel being delivered VS the air entering the engine. That is the likely cause of the idle issue.

Is the parts truck the same year and model?

Joe

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Monday, November 28th, 2022 AT 8:06 PM