Won’t go to closed loop

[hippieman9]

Ok so I’ve been searching past threads and I think now I am more confused LOL. The issue I am having is when checking the CO with my dwell meter it will stay steady at “21” reading 8 cyl scale. 42 if doubled for 4 cyl. (Engine warm of course)

Anyway I’m a bit confused as to what exactly I should be checking.

I have installed a new O2 sensor. I checked the Lambda relay, by installing a known good one, nothing changed.

Ive confirmed the vacuum lines are all installed correctly, although I don’t have a smoke machine to check for leaks.

I wasn’t sure if it’s a poor fuel spray pattern I should check, or an electrical issue.


Thank in advance.

[Bitsyncmaster]

New sensor so now I think you have a missing ground on the engine harness. Most common you missed a ring terminal that should bolt to the engine head.

[hippieman9]

I have also checked the grounds on the passenger side of the intake, all looks good.

[hippieman9]

New sensor so now I think you have a missing ground on the engine harness. Most common you missed a ring terminal that should bolt to the engine head.

I know there is a cluster of wires on the driver side and the one short black wire on the passenger side, with the spade connector, they are all attached and look good.

[Bitsyncmaster]

Pull the blue bulkhead connector and stick it back on. That connector has two ground pins that ground the lambda ECU.

[hippieman9]

Pull the blue bulkhead connector and stick it back on. That connector has two ground pins that ground the lambda ECU.

Ok will do. Unfortunately i won’t be able to till I get home from work

[DMC1890]

Although you replaced the O2 sensor, you still might want to verify the sensor input to the ECU. It should rise to about a half-volt after warmup.

I haven't done it myself, but perhaps you could also disconnect the full-throttle/thermal-switch input to the ECU to make certain they aren't overriding the ECU operation.

[hippieman9]

Although you replaced the O2 sensor, you still might want to verify the sensor input to the ECU. It should rise to about a half-volt after warmup.

I haven't done it myself, but perhaps you could also disconnect the full-throttle/thermal-switch input to the ECU to make certain they aren't overriding the ECU operation.

Where do I check the O2 sensor input? Volts on the wire from the sensor ? Sorry for the dumb question.

[DMC1890]

Sorry, I can't remember exactly where I did that. I may have had a splice somewhere that let me tap into it. I'll try to have a look later to see if I can remember.

[David T]

There are a lot of possible reasons the system won't go into "closed loop". First make sure the frequency valve is buzzing. If it isn't buzzing it can never get into closed loop. Make sure the motor is warmed up and the WOT micro is not "set" or closed. Check that there are no vacuum leaks. If the motor hasn't been tuned up for a while (or you don't know how long it's been) it needs a tune-up. If the mixture is way off, and it doesn't take much, a 1/2 turn one way or the other, it can keep you from getting into closed loop. Finally a bad connection anywhere between the Lambda ECU and it's sensors or the frequency valve can prevent closed loop. There are specific tests you can perform to try to force the system into different pulse ratios. Refer to D:04:15 in your Workshop Manual.