08 Boxster Misfires

[JFP in PA]

Should be.

[vza]

.25 volts at idle to 5v when engine is reved over 3500rpm. Can't identify correct pin for checking resistance. Looks like red/grn and gry/brown wires at solenoid connector.

Edited January 7 by vza

[JFP in PA]

This may start out sounding weird, but bear with me.  You have two pin connectors on the harness coming from the DME to the solenoid, using a multimeter set to at least 12V DC, you should read around 3V on one pin, and battery voltage on the other (engine running).  The low voltage pin is seeing the transistor or fet in the DME that is the ground (yes, I know grounds do not normally show voltage, but in this case it does because of the electronic device the DME uses, it has a low voltage DC signal on it).  The second pin should show battery voltage (~13V DC) when the engine is running.  Obviously, that is not what you are seeing, and as a 9V battery can trigger the solenoid, it looks like the solenoid is good, but the voltage on the harness is low and wavering with RPM's, which it should not be doing.  That wire gets its power from the ECM relay, left side of the engine bay (if memory serves), which may be going south.

[vza]

Hobbyist mechanic so bear with me.  ...1st off not too sure how to check voltage on each pin. Do I ground multi meter to engine and just use the pos lead on multimeter to check voltage from those 2 pins?(one at a time) I just had the multimeter connected to the 2 pins on the connector is that incorrect ? I started investigating DME relay ...is that the same as the ECM relay? There's 2 relays near L tail light in the trunk. One green w 5 pins and one black w 4 pins. Is the 5 pin one the ECM relay? Other may be fuel pump relay.

Also remember both solenoids don't activate with the Durametric. I just checked bank 2 solenoid w the 9v battery and it activated as you know.  Didn't try bank 1 solenoid cause it's not as easily accessed. Would a failing ECM relay cause both not to activate, if so maybe that's the prob. I noticed it's also intermittent, CEL lights blinks sometimes then goes to solid CEL and then it just goes off sometimes. 

Edited January 7 by vza

[JFP in PA]

Yes, positive lead to pin being tested, other lead to ground; you should see DC voltage.  Yes, the DME and ECU relay are the same thing.

[JFP in PA]

Slot #11

[vza]

Ok, thanks John great help. Where is this relay bay in the footwell near the fuse box. Don't recall anything in the engine bay.

[JFP in PA]

That relay panel is under the driver's side dash, it is in the rear on some Caymans.

[vza]

4 minutes ago, JFP in PA said:

 

Ok maybe that's the wrong one in the trunk I found, I'll look under dash and get back. Thanks again

[vza]

I ordered 2 Bosch relays for 17.00(one spare) it was easier than checking all the voltages, especially on bank 1. Figured I'll give it a try. Would a bad relay cause the solenoid in both banks not to activate? Thanks V

Edited January 9 by vza

[JFP in PA]

Without sitting down and tracing the wiring diagram for the car, I would say my answer would be a "qualified" yes as the two different bank solenoids do not act independently of each other, so the simplest system would be one circuit to trigger both.

[vza]

Makes sense. Fingers crossed. Thanks JFP

 

[JFP in PA]

And ten seconds after I posted that, I realized I have to be wrong on that point as the Durametric can activate either one independent of the other, so there has to be separate circuits, at least for diagnostic purposes, and the DME can by throwing different codes tell you that one specific bank is not assuming an active position.  There has to be two circuits.

[vza]

Crap...had my hopes up. Maybe theres 2 circuits downstream from the relay...spitballin here!!  I'll try the relay anyway. See what happens. Maybe the relays totally shot, I did have a hard time starting at one point. 

Car cranked but wouldnt start. Then it did after a number of attempts. 

Briefly looked at wiring diagram. Both Red/Blu are shared with both solenoids maybe thats the issue with the relay? 

 

Edited January 9 by vza

[JFP in PA]

Remember, both solenoids are electrically "hot" when the car is running, regardless of the cam activation, which happens when the DME active position conditions are met (read RPM levels), and the fets create a path to ground, which is what causes the solenoid to move and the cam positions to change, so there can be common wire colors to both that are carrying battery voltage.

[vza]

Right so one part of the circuit is shared...so it still might be the relay....no?

[JFP in PA]

Possible.....................

[vza]

Ok, Ill report back after I try the new relay. Thanks again. V

[vza]

Same results with new relay. I then checked voltage on each wire of bank 2 solenoid. 

14.9 red/grn with little or no fluctuating when revved.

14.6 on brn/gry with lower voltage when revved...maybe down to 10v

So kinda lost here. I guess I could swap plugs/coils see if it follows, doubtful cause they were replaced. 

Then check for low resistance in the wires from solenoid connector to pins for DME. 

Was looking at wire diagrams but couldn't find pin # on any DME connectors for red/grn and brn/gry wires. 

Edited January 14 by vza

[JFP in PA]

It is sounding more like the fets in he DME are not functioning properly.  Again, the way the solenoids are supposed to function is one wire carries battery voltage to the solenoid when the car is running, the second wire runs to the fet in the DME which functions as a gate or switch that changes at a fixed RPM.  In my experience, the wire going to the fet reads low (~3 volts DC) until the RPM target is reached, at which that wire turns into ground and the solenoid activates.  You are indicating battery voltage on both solenoid harness wires, which will never activate the solenoids. 

 

As for the misfiring cylinder #3, electrically there are only three possibles: the plug is bad, the coil is bad, the coil harness connection is bad.  So if you have power at the coil harness connector, and the connector is fully seated, you are left with the coil or plug.  Pulling and replacing the plug is simple enough, and the coil pack can be tested by moving it to another cylinder to see if the fault code reappeared there.

[Vincent Venezia]

Bump

Edited February 22 by Vincent Venezia

[vza]

Ok, Getting back to the issue here. (I took a break) So I have 2 issues the 1.misfires and 2. the solenoids not turning on? I thought the solenoids not engaging would cause the fault code but I suppose the solenoids aren't activated until a certain RPM is reached.   V

[JFP in PA]

The DME has to see the solenoids not activated multiple times before throwing a code.  Which cylinders are showing the misfire?

[vza]

Cylinders 4 and 6. I swapped the coils and plugs with 1 and 3 and ran the car for a bit with no cels. So not sure what that means. 

[JFP in PA]

Could just be a fluke misfire, I'd wait to see if it returns.