1995 Buick Riviera Check engine light

Tiny
JWOOLUMS
  • MEMBER
  • 1995 BUICK RIVIERA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 168,000 MILES
I have a 95' Riviera with a supercharger. The supercharger has been replaced, it has had all new plugs, wires and three new coils. I have had the transmission serviced and have oil changed regularly and add fuel additive every other tank. When drive I feel a vibration and with my experiece I feel it is a combustion issue. After a few minutes driving the check engine light comes on and it is to the point that I can tell when it will happen (usually once I reach 40 MPH and then let off the throttle). The testing device says the check engine light is emmission related and could be one of three things; the EGR valve, the O2 sensor or an electronic fuel sensor. This car is running better than ever and I even get 24 MPG but this rough idle vibration is driving me nuts. One other note; sometimes when I start the car back up after only sitting a few minutes, it has a toughtime staying running so I have to do a power brake take off until it straightens out in a few seconds. Do these symtoms suggest a bad EGR?
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Wednesday, October 15th, 2008 AT 8:44 AM

11 Replies

Tiny
MERLIN2021
  • EXPERT


http://www.2carpros.com/forum/automotive_pictures/62217_GM_DLC95_Older_17.jpg

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Wednesday, October 15th, 2008 AT 4:54 PM
Tiny
JWOOLUMS
  • MEMBER
I have no idea how your post is supposed to help. You asked no question and you show some diagram as to entering diagnostic mode. First off, I have already had a mechanic do that. Second, what am I supposed to jump those two connectors with? Third, how is that going to help?

Why don't you try typing a question or give me some feedback to my detailed post.

I have no idea what you are wanting.
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Wednesday, October 15th, 2008 AT 5:06 PM
Tiny
JACK42
  • MEMBER
Use a piece of wire or paper clip to jump the two and count the flashes, this will give the code that the computer stored. So the vibration feels like a misfire? The way you describe it, it could be an EGR issue or possibly a weak injector. Those 3.8's had some issues with injectors. The stalling after restart could also be an injector issue as well, or possibly a idle speed control motor. Try removing the isc motor and cleaning it with carb cleaner.
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Thursday, October 16th, 2008 AT 12:30 PM
Tiny
JWOOLUMS
  • MEMBER
Hello Jack and thanks for the response. This started after I had the superchager replaced and I thought it was a misfire. I replaced the three coils and it still ran rough so I took it back to the mechanic and he replaced the wires and plugs. This vibration did get less noticeable but it still did not run like it had before. I only replaced the supercharger because the bearings were shot and it was making a lot of noise. The mechanic told me he cleaned the throttle body when he reassembled but I will try and clean the injector item you mentioned.
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Thursday, October 16th, 2008 AT 2:16 PM
Tiny
JACK42
  • MEMBER
Do oyu get the vibration at idle? If so try removing and securing the supercharger belt out of the way and starting it to see if the vibration goes away
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Thursday, October 16th, 2008 AT 2:56 PM
Tiny
JWOOLUMS
  • MEMBER
Yea Jack we have tried that as well. In fact, I was so convinced that it was maybe a warped turbine or misaaligned pulley that I got the supercharger replaced as the company I bought it from gave me a lifetime warranty.
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Thursday, October 16th, 2008 AT 3:26 PM
Tiny
MERLIN2021
  • EXPERT
I did type in the instructions on my post, but sometimes when we upload the pictures, it clears the text, sorry. What I would like to know is if you already read the codes, what were they? This will be of some help, since we are diagnosing over the web! Here are the instructions to do it yourself, use the picyure above. Cross these two terminals as shown, then turn the key on. Count the flashes, a 22 will flash as 2 flashes then a short pause, then 2 flashes, if more than one code is stored, the pause will be longer. The codes will display three times and end with 12. Write them down and post here. This connector is right under the middle of the dash.
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Thursday, October 16th, 2008 AT 3:44 PM
Tiny
JWOOLUMS
  • MEMBER
Hello Merlin,

Sorry to just be getting back but I got pretty ill fo a few days. Today I tried sticking a paper clip into the first two spots of the connector and then turned the car on. I tried the first two from both ends since the plug does not really look like your diagram. I did this several times with each but I saw nothing flashing as in lights or numbers. Can you advise?

Jim
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Monday, October 20th, 2008 AT 3:43 PM
Tiny
MERLIN2021
  • EXPERT
Yep..maybe! Some 95's have the newer OBDII connector, on all 96 and new cars, if it looks like this, scan with an OBDII scanner, Autozone does it free, or you can buy one here.
http://www.2carpros.com/affiliate/uid/merlin2021_1


http://www.2carpros.com/forum/automotive_pictures/62217_DLC96_1.jpg


Hope you feel better!
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Tuesday, October 21st, 2008 AT 1:25 PM
Tiny
MELLOWDE
  • MEMBER
Do not try the paper clip trick. On OBD1.5 as it's called by some all you'll do is burn open fuses under the back seat. And by the way you can get a scan tool to read the code for free at Auto Zone. Not Orielly or Advance though as there brand does not work. You will need the Actron or similar and you must plug the scan tool into the cigar lighter as you need voltage direct from the car or the scan tool will not communicate. I used an Actron 9185 with the obd2 cable. It had the 95 buick riviera in it's software. Get the code but don't do what it says. It will tell you if its an ignition related problem. Most times it's the ignition module that's bad or has a bad contact to the plate it sits on. It must be grounded with thermal grease. If that has broken down or was never applied you will not get good ignition. This is a known issue with the 3.8 but no one will tell you. If you buy a gm oem replacement module it will come with instructions and a tube of thermal grease. The plate on the rear of the module is a cpu like you have in your computer. All ignition passes through this module. Both input from the crank and cam position sensors and the voltage from the cars computer. The like to go bad and they like to take out the coil packs too. Now check all plug wires for short. Go out at night with a spray bottle of water and a flashlight. With the engine running in the dark spray the wires and coils all the way out to the plugs and watch for arcing. Turn the flashlight on to id the location if you see sparks. These are famous for burning open wires. Chared inside of plug boot is a defiinite sign of issue and will cause severe misfire from time to time. Do not use any paper clips in your obd connector on this model. You will need a lift to get to the rear 3 plugs and wires. Access in in the back of the engine from underneath the car while on the lift. I doubt you will be able to jack it up enough to see into the area. Ignore all codes that mention cam or crank shaft position sensors or 18 crank codes etc until you replace the module, coils, wires and plugs. Those codes are often displayed when the problem is actually with one of these items. Process of elimination is key.
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Tuesday, May 21st, 2013 AT 7:51 PM
Tiny
JACKPOT39
  • MEMBER
Excellent answer. Few people know about the module plate with the CPU located under the coil pack. Went out on mine and I played hell trying to find the problem.
Also correct on the 95 Riviera OBD. Trying to find a place to read it is in possible.( I agree NO paper clip trick!)
It is a 1.5 obd or other words a OBD2 plug in with a OBD1 operating system. Few readers have that operating system in its system. (Had to take mine to the college).
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Tuesday, September 29th, 2015 AT 4:44 PM

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