Service engine soon light comes on when slowing down - Third Generation F-Body Message Boards

andy625 · 09-21-2009, 06:00 AM

I've just had my 5.0 1987 Carbbed Firebird (with cat removed) tuned by a diagnostic tuning co. They identified that the emissions were quite high (although its passed the annual MOT test here, with no problems) and that the MAP sensor wasn't connected.

They reconnected the MAP sensor, and got the emissions within the right range. The car now runs better and smells better. However, when I'm cruising at say 60-70mph, and take my foot off the gas to slow down, the Service Engine Soon comes on. If I then put my foot back on the gas lightly, it goes out.

I think there might be a problem with a vacum connection somewhere, and haven't had a chance to have a proper look yet, but I wondered whether anyone else has had similar symptoms??

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andy625 · 09-21-2009, 03:38 PM

I just had a quick look over the vacum pipes, and all seems to be connected ok. The component that I think is the MAP sensor is located on the passenger side of the engine attached to the firewall. The pipe from it goes to a 5 way connector near the distributor, and one of those goes on to the manifold.

I do have one pipe that has a slight leak, I don't know what it does, or if its likely to be the cause of my SES light. Heres a pic of the area. The one thats bad has the tape on it, but I'd be interested to know what this whole assortment of components actually do. I know theyre all related to the fuel cannister and the fuel fumes etc. But can anyone brak it down for me??

andy625 · 09-22-2009, 05:43 AM

bump

Ronny · 09-22-2009, 10:51 AM

I would suggest you need to pull codes from ALDL. Or stop at auto parts store and they will connect for free with their tester.

andy625 · 09-23-2009, 03:22 PM

Quote:

Originally Posted by Ronny

I would suggest you need to pull codes from ALDL. Or stop at auto parts store and they will connect for free with their tester.

Thanks, but unfortunately its not as easy to get the codes read over here in the UK.

I replaced the hose that was bad yesterday. It went from the connector up by the carb down to the cannister at the front drivers corner of the car. However it has made no difference at all to the SES light. It still comes on when I slow down from speed, and goes out when I put my foot back on the gas.

akmusclecar · 09-23-2009, 04:34 PM

Grab a paperclip and bend it so you can stick it in the top right 2 ports in the ADL port. The port is by your right leg under the driver side dash. The codes will appear as blinks from the SES light.

grumpygreaseape · 09-24-2009, 03:01 PM

is there no vacuum hose routing diagram sticker on your car? i believe the map sensor needs its own dedicated vacuum line run directly to a manifold vacuum source. map stands for manifold absolute pressure. it needs to read true manifold vacuum to operate properly.