V6 Discussion and questions about the base carbureted or MPFI V6's and the rare SFI Turbo V6.

Help with back firing and running rough.

Old 10-30-2018, 07:14 AM
  #1  
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Car: 1990 Camaro RS 3.1L
Engine: 3.1L v-6
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Help with back firing and running rough.

I have a 1990 3.1 mpfi and I had a timing chain that had gotten slack in it so changed it. Well then I have a back firing through intake and exhaust. Got the intake one to stop but still have the other. all ignition parts are new dist wires plugs. the only electrical components from one end to the other that have not been changed is the o2 sensor and the map sensor. It runs rough popping through out the rpm range. When I park it and get back in to back out it keeps dying and smells like it's flooding. I did find a problem with the secondary are valve was letting air go both ways all the time, eliminated that still same problem. Help I don't have a lot of money to just buy parts.
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Old 10-30-2018, 10:31 PM
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Re: Help with back firing and running rough.

Originally Posted by Grandpa View Post
I have a 1990 3.1 mpfi and I had a timing chain that had gotten slack in it so changed it. Well then I have a back firing through intake and exhaust. Got the intake one to stop but still have the other. all ignition parts are new dist wires plugs. the only electrical components from one end to the other that have not been changed is the o2 sensor and the map sensor. It runs rough popping through out the rpm range. When I park it and get back in to back out it keeps dying and smells like it's flooding. I did find a problem with the secondary are valve was letting air go both ways all the time, eliminated that still same problem. Help I don't have a lot of money to just buy parts.
Check your timing .
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Old 10-31-2018, 08:09 AM
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Car: 1990 Camaro RS 3.1L
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Re: Help with back firing and running rough.

Timing keeps moving I set it it changes after a few miles.
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Old 10-31-2018, 03:50 PM
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Re: Help with back firing and running rough.

Are you setting it with the est disconnected ?
Have you ohmed out the injectors?
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Old 10-31-2018, 07:21 PM
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Car: 1990 Camaro RS 3.1L
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Re: Help with back firing and running rough.

Yes est is disconnected , no can't get to the injectors to check them. I just cleaned them a little while back right before the timing chain was installed. I had the intake off replacing gaskets that where leaking oil.
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Old 11-01-2018, 05:28 AM
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Re: Help with back firing and running rough.

If your timing is moving, you may have wear in the distributor. How much does it move from when you set base timing (10 degrees), to when you check base again?
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Old 11-02-2018, 07:23 AM
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Car: 1990 Camaro RS 3.1L
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Re: Help with back firing and running rough.

It is a new Distributor, I changed the O2 sensor and it corrected the timing issue. Runs better not popping all the time but once in a while you hear a pop in exhaust. I cleaned the IAC and it pocket it goes into Tweaked the TPS but pulles good in 1st but sluggish in 2nd 3rd is ok but still jumping between drive and overdrive a little too easy. Even on cruise.There is still the slight exhaust leak at the manifold and doughnut but Got to get more money to fix that and change the MAP sensor. Then every electrical part on the car will be new.
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Old 11-02-2018, 09:09 AM
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Re: Help with back firing and running rough.

I have an unrelated question. I have not cat and no smog pump haw can I delete the EGR and not mess the ECM up?
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Old 11-02-2018, 01:02 PM
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Re: Help with back firing and running rough.

Originally Posted by Grandpa View Post
I have an unrelated question. I have not cat and no smog pump haw can I delete the EGR and not mess the ECM up?
you will need to buy a programmer or have the code 32 and mat enable temp set to a maximum value.
tc http://tunercat.com/ or tunerpro http://tunerpro.net/ $88 definition.
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Old 11-02-2018, 05:44 PM
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Re: Help with back firing and running rough.

Thanks I'll have to wait till I can get more money together. Hopefully soon.
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Old 11-05-2018, 05:34 AM
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Re: Help with back firing and running rough.

You can delete the EGR without tuning, but you will end up with the check engine light on. EGR is only active at cruising, its shut off at accel, decel, open loop, etc. I made some block off plates and removed everything from mine. Never saw an issue with MPGs or anything. It won't "mess up" the ECM though. But yes the correct and complete way is to tune it out once it's been deleted.
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Old 11-09-2018, 05:58 PM
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Car: 1990 Camaro RS 3.1L
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Re: Help with back firing and running rough.

Well I found out today that the dang fuel filter was nearly clogged up with rust, go figure I cleaned the tank thoroughly when I changed the fuel pump. But that's what happens when they sit to much and not full of fuel. So I'll go drive it in the morning and see how much of the problem is corrected. I just dread the task of pulling that tank again but I'll go back with new tank sender as mine does not work and pump. Thanks guys for your help.
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Old 11-13-2018, 02:09 PM
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Re: Help with back firing and running rough.

Originally Posted by Grandpa View Post
Well I found out today that the dang fuel filter was nearly clogged up with rust, go figure I cleaned the tank thoroughly when I changed the fuel pump. But that's what happens when they sit to much and not full of fuel. So I'll go drive it in the morning and see how much of the problem is corrected. I just dread the task of pulling that tank again but I'll go back with new tank sender as mine does not work and pump. Thanks guys for your help.
that was my problem. we cleaned out the gas tank but we never could get all the rust out. had to redo the job with a brand new gas tank. wish I had converted to a 4th gen plastic tank.
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