Hi, I have been deeply frustrated with the following problem and and hoping that someone has any ideas to get me in the right direction.

Model: Mazda6
Year: 2003
Mileage: 38,000

Mods:
CPE Intake and MAFci Customizer attached to ECU harness.
Viper791 alarm.
NOTE: both the above mods have been removed and set back to stock. While I have been trying to determine cause of problem.

Problem:
Vehicle doesn't start up. The engine turns over perfectly. The fuel pump initiates. But the engine doesn't catch. Sometimes rolling or rocking the car has helped get the car to finally start up. Often if I wait until midday it starts up fine.

Conditions Under Which Problem Occurred:
Early in the morning and late at night. It appears to happen when moisture levels are high... The problem is intermittent but almost guaranteed to happen in the mornings or evenings. Especially if it has rained.


Steps Taken to Address Problem: Vehicle was taken to dealership for service. Supposedly ran general diagnostics. Replaced fuel pump but problem persisted. Upon taking the vehicle back a second time warranty was voided for modifications to ECU harness. Dealership thinks problem may be with ECU and want it replaced for $1500 along with new $300 wiring harness.

Resolution of Problem: none

Current Status: problem still persists.

_____________________________________
Workshop manual quick diagnostic chart for symptom: "cranks normally but will not start" shows the following checklist:

Fuel Quality
Engine Overheating
Air Leakage from intake air system
IAC Valve improper operation
Vacuum leakage
Ignition coil malfunction
Initial Ignition timing misadjustment
Spark plug malfunction
High tension leads malfunction
CMP sensor damaged

I have been told to check engine crank sensor by a mechanic.

Please send me your ideas. It will be greatly appreciated. Thank you.

 

Now that your warranty is voided, you could try pulling a computer/harness from a vehicle at a pick & pull yard. I know I've seen a few here in Michigan.

Did it just suddenly start doing this out of the blue or did it start doing this right after one of the mods you did? Are you getting spark out of the coil? You could try running some dry gas (ethyl alcohol) through the engine to dry up any water that may be in your gas tank (from condensation.)

 

Yeah the problem happend all of a sudden. Not near the installation of any of the mods.
I am still going to have to go through my own testing for spark etc. I was just looking first for anyone who might be able to get me started in the right direction.

Thank you.

 

With the humidity correlation, I would start with the dry gas (cheap to do) and work your way up the list to the mroe expensive items.

You'll want to put a full bottle in that will treat your entire tank, then burn that tank down to fumes, then repeat it again. Thisshould clear the lines/tank of any water that might be in there.

 

Here is the dealerships inspection note:
Check fuel pressure had good fuel pressure. Check for spark had no ign. Spark on all coils. perform pcm harness inspection. Found a lot of splices in harness and after market PCM controller harness splice into the PCM harness. Pin 88 wire was cut and splice into after market maf controller harness. Poss. Inspect coil wires cyl. 5 G/Y wire had B+ Voltage and black wire car cranking had .5 to .0 voltage. Poss. PCM is faulty. Not sure if that is the fault of the system due to cust. installing after market parts.
I done think it is PCM because I don't understand how humidity would effect the PCM... The car always starts Midday when there is low humidity. It is almost guaranteed not to start if it is high humidity and the engine has cooled down.

 

I don't know man...intermittent no spark at all coils is a wierd one. Sounds like a computer/wiring issue to me. High humidity and a cold engine are harder to start than a warm engine in dry air.

 

The conclusion.

The problem was caused by a broken crank sensor. Oil then came through the broken crank sensor and migrated through the cable plugged into it. The oil migrated all the way out to the end of the cable to the harness and shorted and fried a few wires. Beside the fried wires the computer was also damaged.

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It was a battle getting the car fixed. That is why it took nearly 7 months to get it finally repaired.

When I first brought the car to the dealership they didn't know what the cause was because the computer was sending faulty data. So they replaced the fuel pump and the throttle body. They were able to get car started so I picked it up and drove it home.

Soon afterwards the same problem happened. I took it back to them and this time they decided to call out the after market parts and void the warranty. I decided to take car back and remove all after market parts at this point, even though I was fairly certain they were not the cause. I brought the car back to the dealership and they did another diagnosis. They couldn't find the cause but decided they wanted to replace the wire harness and computer for $5000.

I declined repairs after paying diagnosis fees and took it to another repair facility. They right away determined it was the crank sensor and fried wires. They had the computer tested at a ECU repair facility instead of buying a new computer. It was determined to be functional. After fixing wire problems and crank sensor the car still wouldn't start. Mechanics thought it was part of the cars security system and said I had to take it back to the dealership. I payed $800 to them to for ECU check, replacement of crank sensor, diagnosis and labor.

I then towed the car to the dealership and they didn't want to work on the car at all. I had to get a hold of the manager and was able to finally convince him to have the car looked at once again. After telling them about diagnosis from latest mechanic.

The dealership put 13 hours looking over the wires and found more issues with the wires and that the computer was fried.

So finally after the dealership realized that the car was broken all along from the crank sensor and not the after market parts they decided to cover the new computer, more wire repairs and 3 hours of their time under warranty. I still had to pay 10 hours of work at $120 hour.

I am at least happy that it is finally fixed.

First brought car to dealership for repairs Aug 01 07 - car finally repaired Feb 28 08.