MAF Conversion/Idling issues

[JRPony]

A week ago, I did a MAF conversion on my stock motored 88. Got the PCM, harness and MAF out of an 89LX. I realize there is some adaptation time, but after a week it still runs worse then it did with my SD computer. When cold it barely idles (even stalling at times) and when warm it will idle a lot better, but just not at well as it did before. Under load, the motor performs fine.
I wondering if anybody had ideas on what the problem might be. Is the A9L fuel program more sensitive to temperature (possible problem with ACT/ECT/open loop fuel control)? My first thought would be the MAF I pulled out of the junkyard is not reading properly (I did clean it prior to installation).
I do not believe this to be a mechanical issue as no other work was done to the car other then the aforementioned items. The SD computer idled like a champ when cold and at operationg temp. All connectors are in place and the BAP/MAP vaccum line is plugged. Anybody have ideas?

 

[Daggar]

Disconnect the meter and verify that there's a change. Check TPS. Pull codes. Ensure that BOTH o2 sensors are functional (codes should help with this).

 

[jrichker]

Dump the codes and see what the computer says is wrong…

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Walmart.

Or for a nicer scanner see http://www.midwayautosupply.com/detailedproductdescription.asp?3829 – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $35.

 

[JRPony]

Forgot to mention that there were no faults stored.

 

[vristang]

I do not believe this to be a mechanical issue as no other work was done to the car other then the aforementioned items. The SD computer idled like a champ when cold and at operationg temp. All connectors are in place and the BAP/MAP vaccum line is plugged. Anybody have ideas?

I could be completely wrong here, so let me know if I am.

I thought the MAF cars used Barometric pressure not Manifold pressure (actually vac). Only SD uses manifold vac/psi.
If I am correct then disconnecting the BAP/MAP vac line should help your situation.
You could be showing the computer engine vac when it expects to see atmospheric pressure.

Again let me know if I am wrong, as I am just taking a guess here.

The only other thing I can think of is a repinning error, but that should have shown up as a trouble code?

jason

 

[JRPony]

I could be completely wrong here, so let me know if I am.

I thought the MAF cars used Barometric pressure not Manifold pressure (actually vac). Only SD uses manifold vac/psi.
If I am correct then disconnecting the BAP/MAP vac line should help your situation.
You could be showing the computer engine vac when it expects to see atmospheric pressure.

Again let me know if I am wrong, as I am just taking a guess here.

The only other thing I can think of is a repinning error, but that should have shown up as a trouble code?

jason

The BAP sensor functions the same as a MAP sensor. The only difference is the BAP is reading atmospheric pressure and the MAP reads manifold vaccum. So when doing a MAF conversion, the vacuum line leading to the MAP is disconnected from the sensor and plugged. This is what I did.
Also, I swapped the whole engine harness, thus there wasn't any pin relocation going on. But thanks for the input.
Anybody have any other ideas?

 

[CRASH7772]

Do you have cruise? What about the VSS? I have done the same swap but I have a Pro-M and I did H/C/I at the same time. I had real issues with the SD when I did it but I didn't want to mess with it so I just converted with the 89 EEC and harness. I have idle issues now when cold but I think my intake needs to be retorked because once warm it idles fine. I hit 2-3 of them that I could get at and they were loose and now the problem has gotten better so I need to pull the upper and do them all in order. Did you change anything else. Once my demons are figured out I'm heading to the dyno shop for a SCT custom chip. I don't have cruise so that code and others that apply will be gone with the chip install.

 

[Daggar]

The vac port on the BAP should be left open, not plugged. It's how the EEC tells what atmoshperic pressure is at startup.