86 5.0 In A Maverick Erratic Idle And Running Rich!

Scooby67

Member
Jun 24, 2017
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My friend installed an 86 5.0 Mustang engine in an older Ford Maverick (74 I believe). He used a Painless wiring harness. The computer and throttle body are from a 90 Mustang. It has a custom air intake with MAP sensor installed.
It will start, but the idle varies, stumbles a bit and runs very rich. Seems as if it's dumping fuel for some reason. He's been struggling with this last bit of the install for a month now. Any insight would be greatly appreciated!! Thanks you! Joe
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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In the how to/tech section is a surging idle checklist, run through it step by step and you will likely find the problem:
http://forums.stangnet.com/showthread.php?t=698148
I will add that these efi controls have several grounds that need to be copied when transplanting into another body, I believe they are covered in the checklist, there is also a thread there that covers checking codes, several people have contributed to these tech threads and I can tell you they work, I had several self inflicted problems with my fox untill I found those tech threads.
Good luck, keep us updated on you progress and welcome to stangnet.
 

wbrockstar

Member
Mar 31, 2010
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You dont need a scanner to pull codes either,so dont waste your money buying one.All you need is a short piece of wire to make a jumper out of and a test light (since you dont have a functional check engine light) The test light will flash the codes out,to replace the non existent check engine light.
1) The jumper wire gets inserted between the single terminal (STI) connector and the Signal Return terminal @ the diagnostic port.
2) The test light gets inserted between the (+) battery post and the STO terminal @ the diagnostic port.

I see a possible issue already (depending) The car is running a maf sensor,but you stated it has a map sensor too.MAF uses a BP sensor,not a MAP sensor.The same sensor can be used,but you need to remove the vacuum hose from the map sensor,leave its port open to atmosphere and plug the vacuum hose.
Is that airbox completely sealed,except for the opening on the rear where it receives its air supply from??

I only see a couple small vacuum hoses,so Im not sure how youve got things supplied?? You should have a vacuum hose running from the upper intake to the evr solenoid then another hose from the solenoid to the egr valve?? The solenoid regulates/supplies vacuum to the egr valve,so make sure those hose routings are correct.
To rule out the egr valve,as a possible cause of the rough idle,remove the vacuum hose from the valve and plug the hose.Take the car for a test drive.If the idle issue clears up,trouble shoot the egr valve & evr solenoid.
 

Dan02gt

10 Year Member
Mar 2, 2003
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Greenville, NC
So what's the deal with that custom MAF meter? It's unlike anything I've ever seen. The connector is on the wrong side or it's installed backwards. What's the diameter of the tubing? Is it properly calibrated?

Honestly, I wouldn't test one thing till I put a factory MAF meter and housing on it.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
13,046
4,121
193
polk county florida
So what's the deal with that custom MAF meter? It's unlike anything I've ever seen. The connector is on the wrong side or it's installed backwards. What's the diameter of the tubing? Is it properly calibrated?

Honestly, I wouldn't test one thing till I put a factory MAF meter and housing on it.
Good catch on that maf, it does look backward.
 

Scooby67

Member
Jun 24, 2017
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Thanks, guys. He's going to reorient the MAF sensor into the correct position and make a new housing so the probe extends further into the airflow. If that doesn't correct the issue, we're going to attempt to pull some codes to try and pinpoint the problem.
Thanks for all the info and tips!! You guys are very helpful!!
 

Dan02gt

10 Year Member
Mar 2, 2003
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Greenville, NC
How is he making these housing? A MAF meter is a precisely calibrated device. Housing design, diameter, and air flow characteristics across the metering wires are critical. It's not something you just make.

Please get a stock meter and housing or order a Pro-M meter.
 

Mustang5L5

Mod Dude
Feb 18, 2001
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Massachusetts
Sensor direction shouldn't matter. It's a hot wire manometer type setup that just measures resistance change as air flows across it.

However, housing design is a huge deal. You can't just machine one up and mount a sensor on it. The size of the orifice is a scalable proportion to the overall size of the MAF. This relation is critical, as the ECU bases it's fuel curves on this relation.

The electronics themselves are useless unless the housing is designed with this in mind. If the electronics are just in the main airstream, the ECU is going to be VERY rich as the high airflow will cool the meter's electronics off quickly, and the ECU will scale this up and dump in a lot of fuel.

The 1990 Mustang ECU is looking for a MAF similar to this design. The airflow through the tube portion might be, say, 1:15 scale to the flow through the entire meter. So the ECU scales based on this.
113082139.jpg


I see it's a Duralast DL-3070 MAF, which is the correct electronics for the 1990 Mustang ECU, but you need the matched housing. Either find a 1989-1993 Mustang MAF housing, or pick up an entire 94-95 SN95 MAF with adapter and use that.
 
Last edited:

Scooby67

Member
Jun 24, 2017
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How is he making these housing? A MAF meter is a precisely calibrated device. Housing design, diameter, and air flow characteristics across the metering wires are critical. It's not something you just make.

Please get a stock meter and housing or order a Pro-M meter.
He temporarily remounted the MAF in a housing he whipped up out of 2 1/2 or 3" pipe. The first housing didn't allow the probe to extend far enough into the airflow. I saw him yesterday and he said it's running and idling nicely. I'll have him pick up an 89-93 housing, as suggested above, for the permanaent install.
 

Scooby67

Member
Jun 24, 2017
7
2
13
52
How is he making these housing? A MAF meter is a precisely calibrated device. Housing design, diameter, and air flow characteristics across the metering wires are critical. It's not something you just make.

Please get a stock meter and housing or order a Pro-M meter.
He temporarily remounted the MAF in a housing he whipped up out of 2 1/2 or 3" pipe. The first housing didn't allow the probe to extend far enough into the airflow. I saw him yesterday and he said it's running and idling nicely. I'll have him pick up an 89-93 housing, as suggested above, for the permanent install.
 

Mustang5L5

Mod Dude
Feb 18, 2001
31,104
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He temporarily remounted the MAF in a housing he whipped up out of 2 1/2 or 3" pipe. The first housing didn't allow the probe to extend far enough into the airflow. .
It looks nice, but unfortunately the MAF and housing is a calibrated device that is matched to the ECU. Even though it runs nice, it may not be ideal.

Now, if he was a tuner with something like a Megasquirt and the ability to adjust, he might be able to make it work. But strictly plug and play I'd stick with an off-the-shelf unit
 

Scooby67

Member
Jun 24, 2017
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It looks nice, but unfortunately the MAF and housing is a calibrated device that is matched to the ECU. Even though it runs nice, it may not be ideal.

Now, if he was a tuner with something like a Megasquirt and the ability to adjust, he might be able to make it work. But strictly plug and play I'd stick with an off-the-shelf unit
His customer wanted a fuel injected 5.0 in his Maverick, even though he was urged to simply drop in a carburated, built 302. Therefore, there are some teething pains for him to endure.
 
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