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I have a '95 Jimmy with a VORTEC V6. The engine runs
Sent to Car Experts September 27 08:38 PM

I have a '95 Jimmy with a VORTEC V6. The engine runs rough at idle. I get Missfire codes when the check engine light comes on. The engine runs very rich, but not lot of black smoke. The timing at idle around seems to jump 30 degrees from - to +. The oil pressure seems a little jumpy around idle. The oil pressure is OK, it just jumps up when you touch the gas. Many parts have been replaced including the injector.

 

Optional Information:
1995 GMC Jimmy Vortec V6

Already Tried:
Just about all the sensors. including the invector.

Customer (name blocked for privacy)
Status:  Closed   Value: $30
Answer
September 27 8:42 PM (3 minutes and 27 seconds later)
         
REPLIEDCheck Mark

Greetings! Have u checked fuel pressure?

What is the o2 sensor doing at idle? Has it been replaced?



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PictureAMEDEE -- ASE MASTER TECH -- 98% Positive Feedback on 1098 Car Accepts
ADVANCED LEVEL SPECIALIST
Reply
September 27 8:49 PM (7 minutes and 17 seconds later)
         
Reply to amedee's Post: Yes the fuel pressure is OK. The pump has also been replaced recently.

The O2 sensor has been replaced.

The MAP, Throttle Position and EGR have been replaced.

New plugs, wires, cap and rotor also.
Customer (name blocked for privacy)
Answer
September 27 9:06 PM (16 minutes and 50 seconds later)
         
REPLIEDCheck Mark

What is fuel pressure?

What is the o2 sensor doing at idle?

This information is very important! I cant get u correct info if u give me false readings!



If this has helped in any way, please hit the ACCEPT button. If my answer is unclear or if u need more info, just ask! Thanks!   
PictureAMEDEE -- ASE MASTER TECH -- 98% Positive Feedback on 1098 Car Accepts
ADVANCED LEVEL SPECIALIST
Reply
September 27 9:17 PM (10 minutes and 46 seconds later)
         
Reply to amedee's Post: I don't have the data at hand.

I figured I could get some more ideas besides what regular shops look for. It has been diagnosed multiple times. Each shop checking all the basics like fuel pressure, oxygen sensors and the like. I guess I need to know what would make the timing vary so much at idle. What would make the oil pressure change 20 PSI when just touching the gas pedal. How these two items could be related.

How can I continue this on the weekend, when I can have the car in front of me, to answer all your questions with real up to date info?
Customer (name blocked for privacy)
Answer
September 27 9:26 PM (8 minutes and 53 seconds later)
         
ACCEPTEDCheck Mark

Well with the info I got so far I will do my best!

The only thing I can think of is internal.

First the distributor! Usually when timing bounces around that much, it means the distributor shaft is loose, the gears on the cam or distributor shaft are worn and not contacting properly, or the pickup inside the distributor. Also if the timing chain is loose! Because the distributor is driven by the camshaft which is driven by the timing chain. All these can lead to timing bouncing around. Specaily if the oil pressure is acting up, I would rec to pull the timing cover off and have a look.



If this has helped in any way, please hit the ACCEPT button. If my answer is unclear or if u need more info, just ask! Thanks!   
PictureAMEDEE -- ASE MASTER TECH -- 98% Positive Feedback on 1098 Car Accepts
ADVANCED LEVEL SPECIALIST
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