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Discussion Starter #1
Alright it is been a journey on this car, but I still need the help from the guru. So first let me do a review before diving in.

First of here are the specs on the car:

•1994 mazda mx-6 LS ( for the shell and interior) manual transmission

•Engine 2.5 L V6 from a ford probe GT, I think. On top of the headers, I can see FORD ( how can I know the Gen )

When I first got the car, I had the following behaviors:

•Rough idle

•I could not get passed 75 miles per hour and losing power. I had to constantly downshift

•Very bad fuel efficiency no more than 18mpg.

I ran a diagnostic and got the following codes: 15,16,17,18,23,41,42.

What I have done:
• Replaced O2 sensor upstream ( driver side)
• Replaced O2 sensor downstream ( passenger side)
• Replaced VRIS 1 and 2
• Installed fuel pressure regulator solenoid( it was missing)
• Replaced the spark plug and wire set
• Replaced distributor cap

After those replacements, I ran another diagnostic and got 15, 16, 17. The car was doing better.
My fuel efficiency was 25.6 mpg. Then the rough idle came back so as loss of power.
I ran another diagnostic: 15,16,17,8,5. 8 and 5 were new (I think there are related to MAF sensor and knock sensor).

What I have done again:
•Adjusted the Idle Air Control, since while idling the rpm dropped to 500 with the car acting like it was going to shut down.
o Adjusted to IAC until Rpm stayed around 900rpm during idle.
•While the car was running, I tried to unplug the spark plug wires on the front (2, 4, 6). During that the engine behavior was not getting worse, no change whatsoever.
oReplaced again the spark plug wire set, some would not go in easily. So I used electrical tape to close the gap between distributor cap and boot from the wire

The car is running better, but loses panache when outside temperature is scorching hot. After running another diagnostic, I am still getting 15, 16, 17.

the questions and helps
1. EGR
I know that 16 is related to the EGR. As stated in previous post, the previous owner attempted to do a delete. But quite frankly, it is obnoxious to have your clothes smelling like carbon. So I want to put the EGR on it, unfortunately I cannot find a well detailed vacuum diagram. I have used so far:
• Repairsurgemanual
• Alldatadiy
• Autozone
Any pointer like a well detail diagram or a step by steps video?

2. Code 15 and 17
After changing the O2 sensor twice, I am starting to believe that the problem lays in the PCM/ECU.
Mine has the following info( I will try to mimic the bar code) on it :
3 KL55B
KLL55 18 881B

1. What are the year make and model that will be compatible with 94 mx-6 MTX for a PCM/ECU swap?
2. I noticed that the intake air system is after market. It looks like a MAF from Duralast. Will that means that I need to a do MAF swap?
3. What is a MAF swap and how to do it? ( a step by step guide will be so awesome)

I know that it is a long post but some guidance are much needed.

2,700 Posts
If a bad ECU/PCM was causing the O2 sensor codes, I think it would cause the O2 codes for both banks, not just one bank of cylinders. Are you sure the front bank cylinders are getting a good spark (you did mention difficulty in getting the plugs wires connected to the distributor cap, which is strange)? And is there any possibility the timing belt has slipped, so the valve timing for the front bank cylinders is off (maybe check compression for the front bank, because all will have low compression if the valve timing is off)? Either of those problems would cause low power and fuel efficiency.

The stock engine does not have a MAF (Mass Air Flow) sensor, it has a VAF (Volumetric Air Flow) sensor. It's a black plastic cone, that slides inside a cylinder according to the volume of air flow, while a MAF is heated wires. What does your MAF/VAF look like inside? I vaguely remember some owners replacing their VAF with a MAF, to increase air flow and power, but I know nothing about what else is needed.

Premium Member
422 Posts
If you can borrow another VAF from someone, give it a try. A faulty VAF has been the grief of a lot of people over the years. Either that or you may have a vacuum leak somewhere or vacuum plumbed wrong somewhere. Either of those would possibly explain your issues.

Back years ago it used to be a saying on these forums that we would keep a spare VAF in the glove box because that's how good and reliable they were.
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