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1990 Ford F150 inline straight 6 intermittent misfire

Customer's question: Truck has been looked at by other shops but can't fix the intermittent misfire.

Mechanic's answer: Went over testing procedures to see if there is a possible issue with the PCM.

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Resolved Question:

Intermittent burp, stutter, miss, whatever/

Mechanic's Assistant: What is the model/year of your Ford?

1990 300 inline 6.

Mechanic's Assistant: Are you fixing your 300 yourself? What have you tried so far?

Plugs wires distributor cap egr valve etc. actually alleged best mechanic in the area did all this looking for vacuum advance hose to plug.

Mechanic's Assistant: Have you checked all the fuses? Do you have a wiring diagram?

No

Submitted: 4 months ago.
Answered in 3 minutes by:
3/22/2018
HDGENE
HDGENE, Ford Senior Master/Diesel/Trans
Category: Ford
Satisfied Customers: 6,646
Experience: 28 years Auto experience, Ford ,GM, Chrysler, Asian & European
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Hello, and thank you for using Just Answer! My name is***** me a few moments to review your question and Ill do my best to assist you.

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Customer reply replied 4 months ago
O.K. I'll wait.

Hello, when does this happen at an idle or while driving down the road at times? How many miles are on the truck? Any warning lights on?

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Customer reply replied 4 months ago
Not at idle and random driving down road, seems to need load on to act up.
Customer reply replied 4 months ago
About 124000 miles on truck.
Customer reply replied 4 months ago
No lights on.

Ok, if its happening while driving down the road you may be loosing the rpm signal aka PIP signal for the igntiions system. You can check for diagnostic trouble codes by shorting out the self test connector as shown int he attachment and counting the check engine light flashing. Based on the number of flashes will tell if any cdes are stored. You can inspect the distributor shaft for any play.

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Customer reply replied 4 months ago
It has been diagnosed at a shop and has had multiple different parts replaced ,cap,rotor,plugs,wires,EGR valve,TPS, and new brain box and still has hiccup or buck. We think it might have to do with the vacuum system. Any thoughts?

If there was a vacuum issue it would have a poor idle. this still has a vacuum advance with the electronic ignition on this model year? I dont think it does.

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No codes are stored for the ignition system? Does this truck sit for long periods of time?

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Customer reply replied 4 months ago
ok so maybe a lose distributor or?????? Im lost with it:(
Customer reply replied 4 months ago
it has been sitting for a bit off and on. it only has 124k on it
Customer reply replied 4 months ago
not sure about the codes haven't tried that yet

If there is an ignition misfire I would lean towards an issue with the ignition module, pickup coil in the distributor or the wiring from the distributor to the PCM. Injector flow could be an issue since it is intermittent. Double check for any codes first and follow them first if any are stored. The shop can perform an injector cleaner service and also check for fuel pressure leak down if the injectors are leaking.

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Customer reply replied 4 months ago
injectors were cleaned and presser was tested and good
Customer reply replied 4 months ago
whats PCM

then it is either an ignition system issue or a problem with the valvetrain or fuel quality if the vehicle sits and it has old gas in the tank. PCM is the brain box aka engine control module/powertrain control module. if the valve springs are weak the valves could hang. It may show up on a compression test or using a vacuum gauge the vacuum gauge needle will flicker erratically.

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Customer reply replied 4 months ago
OK we will check those things and hope to hell it works thanks for the help

You are welcome, if you need more help or information please let me know. If I was helpful, please use the 5 stars above to leave a positive rating.

HDGENE
HDGENE, Ford Senior Master/Diesel/Trans
Category: Ford
Satisfied Customers: 6,646
Experience: 28 years Auto experience, Ford ,GM, Chrysler, Asian & European
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