Slightly rough idle and a fouled plug on a low mileage 1990 - ZR-1 Net Registry Forums

Reichert · 02-26-2018

Hi,

So I just took delivery of a 1990 with ~20k miles (here's my intro post: http://www.zr1.net/forum/showthread.php?t=28834). It has previously been driven at least monthly the last year and a half, for 20 or 30 minutes, only in normal power mode.

After several spirited drives of my own now, there are symptoms of a problem in the fuel system:

- Cold start and idle is beautiful. Runs great for a while.
- As the engine warms up, check engine light comes on, and then off again a little later. I pulled the codes and get only H65 (O2 sensor, right bank rich)
- At full operating temperature, idling at a standstill and especially with A/C on, it runs a little rough and causes the flywheel to start knocking a little bit (I am pretty sure this is just a symptom of the rough idle and not a problem in and of itself, but I could be wrong)
- I pulled the plugs, and #4 cylinder is dry fouled (picture below)

I replaced all of the spark plugs since that was easy, but no change in behavior. it still has the original plug wires stamped with "Corvette LT5". So far my best guess is a bad injector, and/or plug wire.

Before diving in and taking apart the intake plenum to diagnose further, I wanted to get your opinions and advice here.

2018-02-26_07-37-00

02-26-2018	#1
Reichert Join Date: Feb 2018 Location: Austin, TX Posts: 104	Slightly rough idle and a fouled plug on a low mileage 1990 Hi, So I just took delivery of a 1990 with ~20k miles (here's my intro post: http://www.zr1.net/forum/showthread.php?t=28834). It has previously been driven at least monthly the last year and a half, for 20 or 30 minutes, only in normal power mode. After several spirited drives of my own now, there are symptoms of a problem in the fuel system: - Cold start and idle is beautiful. Runs great for a while. - As the engine warms up, check engine light comes on, and then off again a little later. I pulled the codes and get only H65 (O2 sensor, right bank rich) - At full operating temperature, idling at a standstill and especially with A/C on, it runs a little rough and causes the flywheel to start knocking a little bit (I am pretty sure this is just a symptom of the rough idle and not a problem in and of itself, but I could be wrong) - I pulled the plugs, and #4 cylinder is dry fouled (picture below) I replaced all of the spark plugs since that was easy, but no change in behavior. it still has the original plug wires stamped with "Corvette LT5". So far my best guess is a bad injector, and/or plug wire. Before diving in and taking apart the intake plenum to diagnose further, I wanted to get your opinions and advice here. 2018-02-26_07-37-00 Last edited by Reichert; 02-26-2018 at 09:58 AM.