Run Problem

The Crown Vic computer uses a different firing order from the HO engine. It will not run smoothly or give the best performance.

This doesn’t prove that the block is a HO block. Some trucks evidently use a HO firing order with a low lift cam (this will result in less than the desired HP output). However, it will definitely prove that a block can’t be HO because the firing order is wrong.

Remove the #1 & #3 spark plugs. Put your finger in #1 spark plug hole. Crank the engine over until you feel compression on #1 cylinder. Slowly turn the engine until the TDC mark and the timing pointer line up. Mark TDC on the balancer with chalk or paint. Put your finger in #3 spark plug hole and crank the engine 90 degrees. You should feel pressure trying to blow past your finger. If you do not feel pressure, repeat the process again. If you feel pressure, it is a HO engine.

No pressure the second time, remove spark plug #5. Put your finger in #1 spark plug hole. Crank the engine over until you feel compression on #1 cylinder. Put your finger in #5 spark plug hole and crank the engine 90 degrees. If you feel pressure now, the engine is not a HO model, no matter what it says on the engine.

Using a small carpenter or machinist square to mark the harmonic balancer off into 90 degree sections may be helpful here.

A 15/16 deep socket & breaker bar or ratchet may be used to turn the engine.

The HO firing order is 1-3-7-2-6-5-4-8.
Non HO firing order is 1-5-4-2-6-3-7-8


You best be would be a Mass Air conversion and a computer out of an 89-93 5.0 Mustang - A9L or A3M.

MASS air conversion instructions from http://www.stangnet.com/tech/maf/massairconversion.html FREE

Revised 2 Aug 2014 to add new links to conversion harness suppliers, diagram for repining computer wiring connector and YouTube video

A9L (5 Speed) computer from junkyard $100-$150
A3M (5 Speed) computer from junkyard $100-$150
A9P (Auto or in a pinch, it will work in a 5 Speed car) computer from junkyard $100-$150
70MM MAF from 94-95 Mustang GT - $40-$70
MASS Air wiring harness kit $30-$85

The whole thing is probably less than $300 using junkyard parts.

A9L computers are 5 speed only
A9P computers are automatic, but will work with a 5 speed.

The conversion harness seems to work well for most folks. It avoids the compatibility problems in using a harness from the junkyard. Simple and cheap, actually less work that swapping the wiring harness.
Conversion Harness kits & parts
http://www.mass-air.com/
http://www.latemodelrestoration.com...ustang-50L-Mass-Air-Conversion-Wiring-Harness

Youtube video how to do a Mass Air conversion using a conversion harness kit (somewhat long but useful)
View: http://www.youtube.com/watch?v=mnnTgXkHU9Q




Wire side 60 pin computer wiring harness connector

Computer side 60 pin computer wiring harness connector



If the idea of moving & soldering wires scares you, here's a list of compatible Mass Air wiring harnesses.

Copied from bbunt302
Just for reference, here's a list of all the compatible years:

89 harness should work for 86-89 as long as you're using mass air.
90 harness will only work in a 90. (because of air bags and dual dash connectors)
91 through early 92 harnesses should be compatible (single dash connector, fuel pump relay under driver's seat)

Late 92 through 93 harnesses may be compatible (single dash connector, fuel pump relay under the hood). You may end up running some extra wire for the fuel pump relay. Comments and input from someone who has actually used the 92-93 EFI harness would be nice.

Larger MAF to go with Mass Air conversion:
94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

*1.) Metal flange adapter http://www.kustomz.com/cat3.html Buy the TR70 for $40-$45 depending on if it’s on sale or not. Or spend some time on eBay looking for one that may fit.
Try AutoZone and ask for 81413 - Spectre / 3 in. Aluminum Intake Mass Air Flow Sensor Adapter at $12.00. You may have to order it online.

*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.

Use the wrong computer and the fuel injectors are squirting at the wrong time. This can play havoc with the fuel distribution and fuel mixture.


Computer & interchange information for 5.0 Mustang

Revised 16-Oct-2011 to add O2 sensor harness warnings

The Mass Air computers from 89-93 are interchangeable with a few exceptions. Just be sure you use the MAF & MAF sensor from the same series computer. The auto transmission computers use a different start circuit than the manual computers. You can use an auto trans computer in a 5 speed car with no problems or changes. I have done it in my original 89 Mustang GT, and I know it works OK. I would recommend avoiding using a 5 speed computer in an auto trans car due to the possibility of damaging the computer’ internal signal ground circuitry.

The odd duck is the 93 Cobra computer, labeled X3Z which is internally calibrated for 24 lb injectors. Use the MAF & MAF sensor from the X3Z computer to avoid problems with the computer's internal calibration. Try and avoid the 93 Cobra computer if you can.

Some cautions about O2 Sensor harnesses need to be observed to avoid damage to the computer.
Only run a 5 speed trans O2 harness with an A9L. Do not run an Auto O2 sensor harness with an A9L. Doing so will damage the computer’s internal signal ground.
Only run an Auto trans O2 sensor harness with an A9P in a car that has an Auto trans. Using a 5 speed trans O2 sensor harness with an Auto trans will cause no crank problems.
See http://forums.corral.net/forums/general-mustang-tech/1094179-oxygen-sensor- harnesses-manual-auto-differences-year-differences.html for more O2 sensor wiring harness info
If you have a damaged computer with signal ground problems, See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix to the computer internal signal ground.

A9L 5.0 89-93 Mustang MAF / Manual
A3M 5.0 89-93 Mustang MAF / Manual
A3M1 5.0 89-93 Mustang MAF / Manual
S0Z 5.0 89-93 Mustang MAF / Manual
D3D 5.0 89-93 Mustang MAF / Manual
D3D1 5.0 89-93 Mustang MAF / Manual
A9M 5.0 89-93 Mustang MAF / Auto
A9P 5.0 89-93 Mustang MAF / Auto
C3W 5.0 89-93 Mustang MAF / Auto
C3W1 5.0 89-93 Mustang MAF / Auto
A9T 5.0 89-93 Mustang MAF / Auto
A9S 5.0 88-93 CA Mustang MAF / Manual
8LD 5.0 88-93 CA Mustang MAF / Manual
8LF 5.0 88-93 CA Mustang MAF / Auto
8LG 5.0 88-93 CA Mustang MAF / Auto
DA1 5.0 87 Mustang SD-SFI / Manual
DB1 5.0 87 Mustang SD-SFI / Manual
DC 5.0 Mustang SD-SFI / Auto
DE 5.0 Mustang SD-SFI / Auto
GJ1 5.0 Mustang
VH2 5.0 86 Mustang SD-SFI

Lourdalfe said:

Ok so your saying I should get a mustang gt pcm because of the ho engine but you recommend going to maf

Click to expand...

Yes, unless you have a cam specifically ground to run speed density, you need to use a Mass Air Computer and matching MAF.

If he had the stock ho Cam can't he run a stock SD ECU? Or is that item in question?

Lourdalfe said:

I beleave it's stock I just didn't realize sd doesn't like anything over stock and ho motors are high output witch means bigger cam then the stock sd motor

Click to expand...

Bigger isn't really the word, but the non ho ecu like said before utilizes a different firing order and is set up for 14lb injectors, not the 19lb units you are running. I'm surprised the car even ran at all. I may have an SD computer kicking around. If I can find it it's yours for the price of shipping. It worked when I pulled it 7 years ago, but I offer no promises on it.

How bout that. It was exactly where I left it all those years ago. That never happens.

Run codes.

Glad to see the ecu helped out.

If the cam really is messing with the MAP sensor there is a cheap solution to smooth the signal it receives. (This is in no way a fix all just something to try) place a small engine fuel filter (lawn mower or the like) in the vacuum line feeding the map sensor. It needs to be 6" or so from the sensor itself, the small volume and paper element act as a signal buffer smoothing the vacuum pulses.

Check the plugs, but definitely get some 19lb injectors. The crown vic parts will hold at idle but you will be running lean and missing HARD with those injectors once you start to give it gas.

Well I'm glad it worked for you. Hopefully it's just a matter of dialing in the timing and ensuring you have adequate fuel.