Engine 1989 5.0 running rough - MAF


New Member
Apr 12, 2021
Sudbury, MA
Hi All - new to the forum, bust have been reading a bunch for months.

I recently installed a 5.0 in my 76 Bronco and have a couple of questions.
The engine (I bought it this way so don‘t have anymore details than this):
  • Engine was rebuilt, new bearings, rings, oil pump...
  • GT 40P heads
  • GT 40 intake (upper/lower)
  • 1.72 Scorpion roller rockers
  • Stock cam
  • 24lb injectors
  • EGR delete
Few question:
Because of the 24lb injectors, I believe I need a matched MAF. The one that‘s on it is part number E9ZF-12B579-AA AFU55-03; is this correct? If not which one do I need? Also, when I replace it how does it get calibrated?

It runs great initially but after driving for 5 mins it get super lean (backfires from intake). If I wait it out it will go back to normal however the lean condition returns intermittently. I read a bunch here and pulled the plug on the O2 sensors and it run fine no backfiring.

If the MAF is incorrect, could that cause the backfiring problem?

thanks in advance.
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Seems like sample tube size is wrong

My setup is similar and I Had 24lb injectors in mine and it ran rich even with the right MAF. Went back to 19lb and it idles better and runs quite a bit better. Still ironing out some things but the 24's were overkill on mine. I know it "should" work but I could not get mine to run right with the stock computer. Not saying thats your issue but something else to look at.
I pulled a set off a crown vic at the salvage for cheap and cleaned them up good. Nicer 4 hole newer style injectors with the correct plugs for the older car. Working great and pretty cheap. Cant hurt to try them.
Measure the inlet and outlet of the sample tube. A red tube is 0.65" inlet, 0.51" outlet.

I have a very similar setup, GT40s, Explorer intakes, 24 lb injector and C&L 76mm. I modified my tube to a unique size and thus far it is idling nice. I have a dual wideband hooked up to monitor AFR and so far the combo is behaving very nicely and as expected.

The red tube will make you VERY lean. If you are game to modify the red tube (normally recommended for 38 lb injectors), drill out the discharge side of the tube to 9/16" (0.5625"). This is what I did (based on some calculations I have been experimenting with).

According to my calcs the clear tube with 76mm MAF will make you about 15% too rich. I also came up with a Clear Tube in a 80mm C&L should work with the 24s. My calcs also put the recommended Blue tube at 1% lean. My modded combo comes in rich 0.5%. I will guarantee my calcs are not perfect, but representative. I you are not planning to run big injectors, give drilling out the Red Tube a try.
Kurisr so I’m clear, making the red one bigger means it will run richer. I’m Ok with drilling it but it looks like they’re hard to find so may not be able to get replacement If I mess it up and it turns out to be something else. Can you provide more details.
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Also what sensor is on your MAF now? I sit the factory 55mm sensor? The C&L was designed to work with it, but you said this was a conversion done at some point? Someone could have put the wrong maf sensor on the housing. Do you have a photo of the part numbers and stuff on the sensor?
Wait a minute, I just looked at the part number for the maf sensor and it's not on the list of compatible sensors.
F2ZF is the number ir should start with according to the 'junk yard parts' writeup.
Where did the harness come from?
76 bronco didn't have efi right?
I just realized he had the part number in the original post and the part number appears to be the correct early 55mm MAF. I have the 92-93 sensor in mine but looking online that F1ZF maf should be correct. Still could be a problem with a 30 year old sensor. Have you sprayed it was cleaner? K&N oil tends to cause the problems over time.