85 Problem
Thread Starter
Racer
Joined: Oct 2012
Posts: 298
Likes: 0
85 Problem
Hi all
I autocrossed my 85 last weekend and made 5 runs without issue. Just after I crossed the finish line on the sixth it started to run rough and backfire through the intake. The engine will start but barely idle (I have to work the throttle) the best I could check the timing was about 4 degrees at 400 rpm. I have 39psi of fuel pressure. What can I check?
Thanks
I autocrossed my 85 last weekend and made 5 runs without issue. Just after I crossed the finish line on the sixth it started to run rough and backfire through the intake. The engine will start but barely idle (I have to work the throttle) the best I could check the timing was about 4 degrees at 400 rpm. I have 39psi of fuel pressure. What can I check?
Thanks
Safety Car
Joined: Aug 2009
Posts: 3,745
Likes: 275
From: Melbourne, Victoria, Australia
Hi all
I autocrossed my 85 last weekend and made 5 runs without issue. Just after I crossed the finish line on the sixth it started to run rough and backfire through the intake. The engine will start but barely idle (I have to work the throttle) the best I could check the timing was about 4 degrees at 400 rpm. I have 39psi of fuel pressure. What can I check?
Thanks
I autocrossed my 85 last weekend and made 5 runs without issue. Just after I crossed the finish line on the sixth it started to run rough and backfire through the intake. The engine will start but barely idle (I have to work the throttle) the best I could check the timing was about 4 degrees at 400 rpm. I have 39psi of fuel pressure. What can I check?
Thanks
Did you have the "check engine" light come on?
If you did the ECM stores all the codes unless the battery has been disconnected. You can use a paper clip and short the top right terminals on the ALDC connector under the dash, the check engine light will flash codes like two flashes a pause and three flashes it will keep cycling thru the codes.
See link below for codes.
http://www.corvettebuyers.com/c4vettes/ecm.htm
I recommend disconnecting the battery (after you retrieve the codes) and let the ecm relearn, i find it fixes most issues. You see the ecm can get itself in a knot if something is out of specificiation and try to COMPENSATE to overcome the problem.
Could be anything you are only guessing until you look at what codes have been stored, disconnect the ecm connector near battery or disconnect the battery for say 10 seconds and reconnect.
Start her up and take her for a drive if she runs ok, after 20 mins driving the ecm will relearn to manage the engine and the idle and performance will be back to normal.
Good luck
Thread Starter
Racer
Joined: Oct 2012
Posts: 298
Likes: 0
The check engine light is not on. I only comes on when I start it for a few seconds then it shuts off. I can barely keep it running. Too much throttle and it backfires out the intake. The distributor is tight so I don't think it moved.
Safety Car
Joined: Aug 2009
Posts: 3,745
Likes: 275
From: Melbourne, Victoria, Australia
That usually fixes 90% rough running or problems when the engine doesnt want to run properly, you will be surprises how a ecm reset fixes a lot of issues.
The Mass airflow sensor can cope with a backfire or two, they are not as fragile as people think. If that failed you will get a MAF code.
The standard injectors are known to fail, check you have spark at the spark plugs. If you do check all cylinders are getting fuel, a bad injector will mean that cylinder is dead. Best way to check is from cold run the engine for 10 or 20 seconds and shut it off, now check the temperature at the exhaust manifold they should all be hot to touch.
If one is cold lok at the injector connector loom (people tugg the injector harness to remove them from the injectors) that usually results in a broken strip of metal in the connector.
Le Mans Master
Joined: Jul 2004
Posts: 6,213
Likes: 694
From: Clifton Park, NY ............Clearwater, FL ... 85 Original Owner
before you do anything simply unplug your MAF and see if it runs better.
Mine did the exact same thing last spring and no code. Replaced and good to go
Mine did the exact same thing last spring and no code. Replaced and good to go
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Thread Starter
Racer
Joined: Oct 2012
Posts: 298
Likes: 0
I unplugged the MAF and it started right up and idled fine but if I try to give it any throttle it still backfiring. Is that normal for the MAF being unpluged?
Le Mans Master
Joined: Jul 2004
Posts: 6,213
Likes: 694
From: Clifton Park, NY ............Clearwater, FL ... 85 Original Owner
Thread Starter
Racer
Joined: Oct 2012
Posts: 298
Likes: 0
Le Mans Master
Joined: Jul 2004
Posts: 6,213
Likes: 694
From: Clifton Park, NY ............Clearwater, FL ... 85 Original Owner
That's a great price with the coupon