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Discussion Starter #1
Hi everyone, My freshly bought Seville ('92 with the 4.9l HT engine) has developed a weird problem : engine runs fine but when I put the headlights on or touch anything electric, the RPM gets significantly lower and the engine doesn't rev smoothly anymore. Also the dash's VFD panel gets dimmer when I put the brake on. The battery is brand new and reads 14v on the dash. I also cleaned the fuse box's contacts with no success.
Any opinion?
Regards,
Joel
 

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Discussion Starter #3 (Edited)
When I bought the car it had a bunch of codes that came:
e031 H Shorted MAP sensor signal
e052 H PCM memory reset
e091 H PRNDL Switch problem
I033 H Loss of Supplemental Inflatable Restraint Data
I039 C Loss of Road Sensing Suspension Data
I052 H Keep Alive Memory Error
A047 C Low Refrigerant Charge
A015 H Sun Load Sensor Circuit
R021 H Driver Initiator Circuit Resistance High
R034 H Dual Pole Arming Sensor Ignition Feed Open

I cleared all the codes and now the AC works again. The original battery was shot so it has been replaced.

We worked on it a bit today. We found the side white lights that come with turn signals were missing bulbs (maybe some local regulation thing) and in the rear right tail light one bulb was a single filament bulb instead of a dual filament one causing a short. The dash does nor dim anymore with turn or stop signals. It still hiccups with headlights on though. I have 14.2V at the alternator but only 13.6 going to the big red wire on the fuse box.

EDIT:
I came back to see if codes had popped again and these showed up:
E031 H Shorted MAP sensor signal
E052 H PCM memory reset (my father fussed in the fuse box...)
I022 H Panel Dimming Switch Pot Circuit (I forgot it on ON while leaving the car at first, did that trigger a code?! We touched a lot of lights bulbs too)
I039 C Loss of Road Sensing Suspension Data
There's definitively something with the MAP sensor as the code comes back, the car's exhaust stinks and it failed emissions...
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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20,220 Posts
check the grounds -
 

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Discussion Starter #6
Thanks for your answers! Eventually a new MAP sensor from Rockauto showed up (along with new rear air struts, front ball joints, and rear brake pads and discs, quite a lot of unrelated work! ) when I finally could start the engine, it started immediately and ran smoothly. I didn't expect this huge engine to be so snappy! It stalled on a test drive, about a Km away from home, then idled very rough, the tachometer playing yoyo between 0 and 2K RPM, then got fine and it never happened again for the remaining 10Km.
I think it was an air bubble that snaked in the gasoline line.

Any thoughts on that?
 

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Discussion Starter #7
Well problem not solved yet!
My father took it for a drive (early morning, headlights on) and the engine got rough and stalled on the highway, leading to a backfire that exploded the muffler like an old can!
573646
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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20,220 Posts
check the fuel injectors -
I suspect you'll find one or more stuck ON - constantly dumping fuel -
 

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Discussion Starter #9
Thanks for the advice :) But the problem showed up only with lights on or any strong energy demand. Stuck injectors would do the problem anytime right?
Meanwhile the service manual I bought on ebay showed up and I started again checking the grounds, with the list helping. I found one that I did not notice, call me stupid, the big one near the battery under the front shroud was all loosy goosy ! I drove around 100km (60miles) yesterday, smooth drive (except for the muffler vaguely put back to shape but still leaky as hell), no worries at all. Let's pray for the best but I'm pretty confidant that this loose ground was the cause (voltage loss giving misfires or injection problems) !
 
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