I'm currently at my local mazda dealer (going on 8 hours now). Got a compression test this morning. Car was running fabulous before the test. Get the car back, and it backfires under load and acceleration. Plugs, plug wires, O2, and fuel filter were changed 1 week ago by me and car was running perfectly. Compression check came back fine. We've changed out 2 plug wires (with AC delco....only ones available), because the tech ruined one of the OEM wires (pulled the wire out of the clamp where it connects to the coil).

Anyone have ANY ideas for us to try? I'm supposed to sell the car tomorrow, which is why I was getting this compression check done, and now the tech here has somehow made my car not run right. Anything we could try would be helpful.

 

Check the vacuum line going to the boost/MAP sensor on the driver's side firewall. It's REAL easy to bump it off when working in that area, and will make the car run like garbage.

Dale

 

Already did. It's connected. Any other ideas? The tech didn't "deactivate" the coils from firing during the compression test. I can't remember, but is that necessary? At one point one plug wire was pulled out of the "connector" on the coil side. The "connector" (the part that gets inserted into the coil) got stuck in there.....could this have shorted the coil?

 

Have you checked to make sure the plug wires are on the right plug/coil combination?

 

have you tried pulling ECU error codes

 

description of ECU limp mode - car will only let you throttle a tiny bit (if you have boost gauge just as you start to get boost car will buck and back fire). but if driving car under low throtlle car drives and idles fine

 

Anyone know the reasons why it would suddenly be put in limp mode? The car was running perfect before I came in to get the compression test. Upon getting the car back from the tech, it's suddenly in limp mode. The only things he touched, were plugs, plug wires, and the relay to kill the fuel. ANY ideas why it's in limp mode.

 

12, 13, 18, 51 were the codes on the blinking CEL. Amazing, the dealer here doesn't have a diagnosis tool for the FD. lol.

 

OK. Was told that I need a TPS sensor and a Boost/MAP sensor.


My question, is how in the **** do those two things both get fucked up during a compression test? Is there anyway it's possible? It just isn't making sense to me because the car was running perfectly that morning on my way to mazda for the comp test. I'm open to any ideas as to what could have caused this.

 

have you reset the ecu? or at least pulled the ground off the battery for a few minutes?

maybe the morons fucked up the adjustment of the TPS sensor while they were monkeying around. try adjusting it like in damian's thread.

 

Thanks for the link alberto. I'm at work now, and I've just checked out Damian's thread, and I'll give that a shot when I get out of here this afternoon. Thanks for the tip.

 

Well, the service dept has closed up for the rest of the weekend with my car inside (which is nice......but unfortunately unaccessable to me now). So I guess I'll work on it monday morning.

I'm guessing the TPS sensor might have gotten out of adjustment somehow during the compression test. I'm not sure why as it's really not close to where he'd be reaching, but I'm having a difficult time coming up with scenarios as to why the car suddenly wouldn't work when it was a simple compression test.

Anyway, thanks for all the input, and if anyone else has any ideas, PLEASE post them up.

 

Before you let those guys sell you anything I would reset the ecu and see if you have any check engine codes. Mine was running like that too after a rebuild and I reset the ecu and now it runs fine.

 

I'll definitely do that on monday. Unfortunately when I was there this morning, I didn't realize they closed the service area at 1pm and I was stuck at work until 1 and didn't make it there before they all left. At least it's safe inside. (Hmmmm, with the techs.......maybe not so safe ).

But I'll definitely do that on monday. Thanks.