Engine running rich at idle and up to 30 mph
Thread Starter
Junior Member
Joined: Apr 2004
Posts: 2
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From: Ingolstadt, Germany
Car: '91 Firebird, '88 TransAm
Engine: 3.1 V6, 5.7 V8 TPI
Engine running rich at idle and up to 30 mph
Hi,
I hope you guys can give me a few hints, first posting here, although I've been a reader for years. I got 2 3rd Gens. here in Germany, an '88 5.7L TPI, and a '91 V6.
I got a problem with the '91 V6, it's running rich during idle and up to speeds of 30 mph. When going 55 mph BLM is at 127 and INT at 128, so that's fine.
BUT, when idling the BLM is at 100, and INT going down to 70-80. Then it goes to Open Loop and when going back to Closed Loop the BLM is still at 100, and INT starts at 128 and goes down again.
According to my ScanTool the engine is running rich, and rarely going to lean.
O2 Voltage is constant then at 0.62-0.80. Unless the INT goes down to 70, then it's running lean until the INT goes up again, for a short while.
The O2 Sensor is new. So I know it's good, and everything's fine when going faster. IAC seems to work fine, and I cleaned the TB passage. MAP seems to work fine, spark plugs+wires+distributor cap are new. No trouble codes.
No exhaust leaks. Vacuum lines seem to be fine. Compression on all cylinders 160 PSI, except 1 at 148 PSI. Everything stock, no mods.
What can I look for ? Fuel Pressure ? Leaking Injectors ?
What else can cause this ? Air pump ? EGR ?
Checked the fuel pressure today, 47 PSI w/ pump running, 45 after, still 45 after 15 minutes, 25 after 75 minutes.
So everything ok I guess ?
Any help is appreciated,
Thanks
I hope you guys can give me a few hints, first posting here, although I've been a reader for years. I got 2 3rd Gens. here in Germany, an '88 5.7L TPI, and a '91 V6.
I got a problem with the '91 V6, it's running rich during idle and up to speeds of 30 mph. When going 55 mph BLM is at 127 and INT at 128, so that's fine.
BUT, when idling the BLM is at 100, and INT going down to 70-80. Then it goes to Open Loop and when going back to Closed Loop the BLM is still at 100, and INT starts at 128 and goes down again.
According to my ScanTool the engine is running rich, and rarely going to lean.
O2 Voltage is constant then at 0.62-0.80. Unless the INT goes down to 70, then it's running lean until the INT goes up again, for a short while.
The O2 Sensor is new. So I know it's good, and everything's fine when going faster. IAC seems to work fine, and I cleaned the TB passage. MAP seems to work fine, spark plugs+wires+distributor cap are new. No trouble codes.
No exhaust leaks. Vacuum lines seem to be fine. Compression on all cylinders 160 PSI, except 1 at 148 PSI. Everything stock, no mods.
What can I look for ? Fuel Pressure ? Leaking Injectors ?
What else can cause this ? Air pump ? EGR ?
Checked the fuel pressure today, 47 PSI w/ pump running, 45 after, still 45 after 15 minutes, 25 after 75 minutes.
So everything ok I guess ?
Any help is appreciated,
Thanks
Last edited by TransAMan1986; Feb 11, 2007 at 11:38 AM.
Senior Member
Joined: Jun 2006
Posts: 503
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From: Desert Heat
Car: 90 RS/90 Z-71/73 Vega
Engine: 3.1/5.7 TBI/5.7
Transmission: 700R4/700R4/350turbo
Axle/Gears: 3.23/3.42/3.42
Your car sure has issues?..the process of elimination is next on your list.A number of things can cause your symptoms.Wrong size injectors,a vacuum leak you havent detected,possible faulty ECM.My car 90 3.1 recently blew a new O2 out and a few weeks prior I found the purge solenoid was stuck open,creating a huge vacuum leak.The additional air will cause the ECM to think the engine is in a low vaccum or load increasing injector pulse width,in turn increasing fuel.Make sure the MAP vacuum line is good(no holes) also make sure the MAP voltage is between 3-5 Mv key on /eng off and either manually apply 10 inches of vacuum to it or start the car and watch the voltage,it should drop.If it doesnt your MAP isnt reacting to the vacuum change.I had a remanufactured computer in my ride and had to go back to the original one...dont buy remanufactured ECM's.Good Luck
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