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Hows it going everyone i have a 89 mx6 gt that is giving me multiple cell codes an is in a limp mode. When I ground the green connector I get this series of flashes.
5 quick, 8 quick, 3 long, 4 quick, 4 long, 2 quick an it repeats itself. Everything was in perfect running conditions started the car up an this happened. The car is in a limp mode cant go over 3k rpms really makes no boost. Spools turbo at idle super fast, 2k rpms an shes whistling loud. Its running super crazy rich. Ive never seen this before. What would cause multiple codes an a serious limp mode instantly like that. Whats failed??? Any help would be appreciated thanks.
 

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Update: I replaced the battery terminals today, also replaced the bolt that is used to ground the white grounding block to the inner fender. I inspected the grounding block but didnt really mess with it just took a wire brush an tried to get everything nice an clean. The previous bolt was rusty. After doing this an resetting the ecu, I turn key to on pos check engine light comes on code 42. Ok. Start it 5-10 secs throw a code says code 08 an code 42. So all I did was change the terminals, an scuffed up the metal that the bolt goes thru on the grounding block an new bolt. I no longer have a code 05, or 34 as previously.

So then I change the ecu out with another i have an repeat same process. Turn key to on pos get code 42. Start the car an i get no check engine light but the car is idling at 1800-2k rpm surging between there. Now this is my first time swapping out stock ecus an trying it. Interesting how 2 different stock ecus get 2 different responses. Weird.

Hooked back up the original ecu start it back up throws code 08 in 5-10 secs.

I have tried 3 different maf's an i have tried 2 seperate complete throttle bodies an it throws this code everytime an then puts the car in a limp mode where you can barely drive it. I have smoked tested hooking up vaccum to the nimple of the center of the intake manifold an had 20 psi on the air compressor an got no smoke to come out anywhere. Im completely stumped here?? Thanks for your help.
 

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Codes:
05 Knock Sensor or Knock Control Unit
08 Vane Airflow Signal (VAFSIG)
34 Idle Speed Control Solenoid Valve (ISC)
42 Turbocharger Boost Control Solenoid Valve (BOOST)

Code 5 and 8 are putting the car in limp mode and making it run rich.

What could cause multiple codes at once:
Grounds, the ECU/device grounds are white plugs that bolt to the cars body, they have multiple black w/greenish stripped wires going to them, there is one between the battery and inner fender, there is one on the passenger side in the same spot the power antenna motor is on the drivers side and there is a ground harness plug behind the ecu (easier to see from the drivers side). There are more but don't recall where.

The extra fuel is spooling the turbo up like launch control does on some cars.

Is it running like crap to 3000rpm, slow as can be, a little throttle or foot to the floor the car runs the same?

The only thing I have seen that will stop the engine from revving past 3000rpm and running like crap the hole time is ECU failure. This happened twice with 88-89 gt's and once with a 92 GT, symptoms where the same all three times, car ran like shit, wouldn't pass 3000rpm, runs so badly I never even shifted to 2nd gear out of fear (all 3 times).
The good news for you:
I couldn't pull any codes from the ecu, wouldn't even give the single ECU flash when connecting the test connector.

Also all three times the boost cut chip was fine, pulled them out and put them in another ECU and the cars ran the same as before.

1-Make sure the three harness plugs at the ECU are connected to it properly (disconnect and reconnect if necessary).
2-Reset the ECU, remove battery -, hold brake for 10 seconds, Reconnect the Battery -, reconnect test connector, turn the key to pull the codes. If the check engine light wont flash most likely the ECU is dead.
3-If the codes are still present than check the harness ground plugs I mentioned above, you can also look into the Knock sensor, Idle control solenoid and VAF, I know the VAF gets a ground signal through the harness, but for the idle solenoid and Knock I am not sure how they work, for the idle the ecu could send +voltage and Ground and simply vary or pulse the signal based on RPM or does the solenoid valve ground to frame the ECU sends +V to operate it and the solenoid sends +V back to the ecu for position reference? ... So using the workshop manual you will be able to find out if and where ground is sent to these 3 devices and which prong to check on the wire harness plug.
Find the plug, locate the ground pin in the plug, unplug the knock/isc/vav/boost solenoid, test with a multimeter + to battery 12V+, - to ground pin in the plug (Harness side), may have to turn the key to on.

Can't remember if you have any fuel modifications on your car, if you do that could explain the turbo spooling at 2000rpm and would tell me your base fuel pressure is set too high. The crappy adjustable FPR's I run default to 40psi at atmosphere (0 vacuum) no mater where idle pressure is set, running a 255lph pump I run 21psi idle pressure. Yes I can adjust Idle A/F's using the VAF bypass screw but that just adds air which means the engine is still burning the same amount of fuel, the idle will go up as air is added and the idle adjust screw must be adjusted and with all these steps it would seem to achieve proper A/F and proper idle with factory idle fuel pressure but millage went from 12mpg to 14mpg by running 21psi fp at idle. (94 octane, 3 cars 14 years no issues).
 

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Update: I replaced the battery terminals today, also replaced the bolt that is used to ground the white grounding block to the inner fender. I inspected the grounding block but didnt really mess with it just took a wire brush an tried to get everything nice an clean. The previous bolt was rusty. After doing this an resetting the ecu, I turn key to on pos check engine light comes on code 42. Ok. Start it 5-10 secs throw a code says code 08 an code 42. So all I did was change the terminals, an scuffed up the metal that the bolt goes thru on the grounding block an new bolt. I no longer have a code 05, or 34 as previously.

So then I change the ecu out with another i have an repeat same process. Turn key to on pos get code 42. Start the car an i get no check engine light but the car is idling at 1800-2k rpm surging between there. Now this is my first time swapping out stock ecus an trying it. Interesting how 2 different stock ecus get 2 different responses. Weird.

Hooked back up the original ecu start it back up throws code 08 in 5-10 secs.

I have tried 3 different maf's an i have tried 2 seperate complete throttle bodies an it throws this code everytime an then puts the car in a limp mode where you can barely drive it. I have smoked tested hooking up vaccum to the nimple of the center of the intake manifold an had 20 psi on the air compressor an got no smoke to come out anywhere. Im completely stumped here?? Thanks for your help.
Are you running the turbo boost solenoid (code 42?).
Stop swapping parts.
Put the 2nd ECU in plug the test connector in, start the car, adjust the Idle control screw on the top of the throttle body to 800rpm and disconnect the test connector (this is how you teach the ECU idle RPM), if the surging continues the idle speed control valve on the throttle body is shot or there is still a ground signal issue and the 2nd ecu hasn't picked it up yet.
Setting idle at the TB and idle A/F with the VAF screw while the test connector is connected can only (based on the available sensors and me guessing) teach the ECU what rpm pulse (from disi) to chase for idle using the Idle speed control solenoid and what voltage from the narrow band O2 sensor to chase at idle using pulse to the injectors.

The Idle Speed Control Solenoid can only control idle within a certain window/range, 2000rpm would be it's current preset idle position, the idle is too high so the ecu shuts the solenoid valve as far as it can, 1800rpm, that is still too high so the ecu sends the solenoid preset idle position voltage 2000rpm and tries to correct it from there again and repeats and repeats...
 

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The high idle can be from changing to many parts at once. The idle adjust and Vaf Adjust screw are manually set at the factory. Because of the simplicity of the ECU you can change the VAF or the TB without affecting idle or idle A/F's because they are decided by idle and O2 signals to the ECU.
However by swapping ECU's, TB's and VAF's if at factory someone over tightened the VAF flap bypass screw and opened the TB bypass screw to compensate and that throttle body is used on a car with a normally set Vaf bypass screw the amount of air passing the throttle body idle bypass will be enough to run higher rpm than the Idle control solenoid valve can control.

Also there is a heat/coolant operated valve that is next to the idle control valve, if it is seized opened it will allow too much air passed the throttle body for the electric valve to control.
 

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Discussion Starter #6
Update: So I hooked back up my standalone ecu an i noticed that it was bouncing .41-.42 volts with the key off an well that jist sent a big red flag off in my head.. That is not normal an has never done that. So now i plug back in the original stock ecu an go searching for the other grounding block located below the passenger headlight assembly, I had no idea about this until you told me Carnage that there was another one. See the first time i had 4 codes stock ecu, removed the grounding block on the inner fender by the battery cleaned the metal where the bolt goes thru an replaced the bolt, got 2 codes instead of 4. So fast forward this time I removed the metal connector out of the plastic connector on both grounding blocks, wire brushed them shiny clean, inspected all the connectors inside the plastic housing, couldnt see any signs of corrosion at all put it all back together reset ecu, started it up an it hasnt thrown a check engine light since. Like wtf?? Now my idle was still jacked an serging tween 16-1800rpm but i looked at the screw set depth on my previous TB an realized how much more mine was screwed in versus the replacement, so I put the test wire on as you stated Carnage an began to adjust an idle smoothed rite out purrs like a kitten. Waiting on my new o2 sensor for wb ruined last one, then I will recheck. Thanks Carnage for the info on the grounding block by the pass an the tb adjusting.
 
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