Backfires or pops through intake under load

FRITZ HYATT

MEMBER
1994 FORD F-150
5.0L
V8
2WD
AUTOMATIC
238,000 MILES

When in gear and slight acceleration the motor backfires or pops through intake and loss of power occurs until more gas is applied then it takes off and accelerates.

Monday, August 19th, 2019 AT 7:36 PM

5 Replies

JACOBANDNICKOLAS

MECHANIC
108,164 POSTS

Welcome to 2CarPros.

The issue can be the result of a few things. First, take a look through this link to see if anything helps.

https://www.2carpros.com/articles/engine-backfires-while-running

Next, I need you to see if there are diagnostic trouble codes stored in the system. This has an OBD1 system. Here is a link that explains how to retrieve codes. You will need a test light to perform this.

https://www.2carpros.com/articles/ford-lincoln-mercury-obd1-1995-and-earlier-diagnostic-trouble-code-definition-and-retrieval

Let me know what you find.

Joe

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Monday, August 19th, 2019 AT 8:58 PM

FRITZ HYATT

MEMBER
2 POSTS

I read codes from check engine light flashes. I read as 111 pause 111. Or is this a 33, or do I need to use the test light method for codes? We cleaned maf, replaced fuel regulator, replaced a cracked hose on intake. None of this solved the problem of intermittent bogging down and then a pop out through air intake when in gear and slight power load. If you let off the gas for about 20 seconds problem clears power is restored but will bog down again about 20 seconds later under load in gear. Starting to wonder if it's ECM?

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Wednesday, August 21st, 2019 AT 6:32 PM

JACOBANDNICKOLAS

MECHANIC
108,164 POSTS

Welcome back:

The 111 indicates the system passed the test.

Have you checked fuel pressure? Based on your original description, it sounds like it's starved for fuel.

Let me know.

JOe

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Wednesday, August 21st, 2019 AT 8:23 PM

FRITZ HYATT

MEMBER
2 POSTS

Yes, fuel pressure was running 39 psi. We also swapped EGR and coil from a donor motor which changed nothing. It recently had a fuel pump replaced to rear tank by previous owner. The front tank was removed he said it didn't work, whatever. We put new cap and rotor on it. I cannot get any code from Koeo or koer now. Not even the 111. May take out ECM and look at it next. Just bought this truck and got the problem dumped on me as they did not tell me it was running rough intermittently.

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Thursday, August 22nd, 2019 AT 3:32 AM

JACOBANDNICKOLAS

MECHANIC
108,164 POSTS

When the problem is happening, does it feel like a misfire or as if it is a throttle issue. It clears up so I have thoughts, but can't confirm without being there.

I'm starting to question of the crankshaft position sensor or a camshaft position sensor issue. The cam sensor's info is used by the PCM. The PCM uses this information for fuel injector timing and calculating ignition timing advance.

The vehicle also has a profile ignition pick up which functions as a crankshaft sensor. The Profile Ignition Pickup (PIP) sensor is a Hall-effect type switch located in the distributor. It sends the Powertrain Control Module (PCM) information on engine speed and crankshaft position. If that is failing, it is possible for these symptoms. However, most times when they fail, the vehicle doesn't run or there is no change in the poor running condition.

See pic 1 for the PIP

Image (Click to make bigger)