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.

[hippieman9]

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.

David,
When I jump the Rpm relay, the FV buzzes. WOT switch seems to work. (I don’t have a smoke machine) to check for vacuum leaks, (any common places?)
I’ve installed new Bosch silver plugs, it has recent cap rotor and wires.

[David T]

Some very common areas of vacuum leaks;
Injector seals
Cold start valve plumbing
Idle motor plumbing (especially that "O" ring seal underneath the mixture unit, the one that is hard to see!).
All of the small vacuum hoses (also double-check routing)
Vacuum advance solenoid
Tamper-proof seal on the mixture unit (or whatever is stuck in there!).

With a smoke machine I have seen a lot of unusual leaks too. The vapor canister, intake manifold, vac hose to the brake booster, Fuel tank evap system, etc. Do as good a visual inspection as you can.

Make sure the air filter is clean. If the injectors aren't spraying equally and with good patterns and all opening at close to the same pressure it can be hard to get a good A/F reading.

[hippieman9]

Some very common areas of vacuum leaks;
Injector seals
Cold start valve plumbing
Idle motor plumbing (especially that "O" ring seal underneath the mixture unit, the one that is hard to see!).
All of the small vacuum hoses (also double-check routing)
Vacuum advance solenoid
Tamper-proof seal on the mixture unit (or whatever is stuck in there!).

With a smoke machine I have seen a lot of unusual leaks too. The vapor canister, intake manifold, vac hose to the brake booster, Fuel tank evap system, etc. Do as good a visual inspection as you can.

Make sure the air filter is clean. If the injectors aren't spraying equally and with good patterns and all opening at close to the same pressure it can be hard to get a good A/F reading.


Ok great thank you... I will double check all this tomorrow. I know it has new fuel lines, new style fuel pump. Replaced all hoses for evap system , new check valve , gas cap and seal..

[David T]

Wholesale replacement is great but you have to watch out for two potential problems. You can get defective parts and you can install them improperly. Everything that was touched could be a problem till it is proven to be OK. Just because the parts are new does not mean they can't cause a problem. I like to do things in steps so if anything goes wrong I know what was most recently done so I don't have to go over everything to find the problem.

[hippieman9]

Wholesale replacement is great but you have to watch out for two potential problems. You can get defective parts and you can install them improperly. Everything that was touched could be a problem till it is proven to be OK. Just because the parts are new does not mean they can't cause a problem. I like to do things in steps so if anything goes wrong I know what was most recently done so I don't have to go over everything to find the problem.

LOL, Yes I agree, I have had brand new alternators fail 1/2 mile from the house. I always say anything man made, mechanical or electrical, can fail.

[hippieman9]

Ok following the tests in the manual, I get
Test A 46°
Test B 46°
Test c 60°
Test D 20°
Test E 50°

All doubled for the 4cyl scale.

[David T]

Ok following the tests in the manual, I get
Test A 46°
Test B 46°
Test c 60°
Test D 20°
Test E 50°

All doubled for the 4cyl scale.

Check the wiring from the O2 sensor to the ECU. Test C should be 87 minimum. Also check the grounds. Refer to the schematic on D:04:12

[hippieman9]

While the engine is running, i sprayed a little brake clean around the intake and injector seals, I notice that the engine starts to stumble, wondering if it has a bad injector seal.

[Bitsyncmaster]

Since everything seems to be working but your still holding steady dwell with the value you get with a cold or disconnected O2 sensor I think you have to see it that O2 signal is getting to the lambda ECU. Hard to tap into that sensor wire since it is shielded. Maybe you can pull the ECU connector cover off and be able to measure the voltage with every still hooked up.

Working lambda the sensor voltage should be 0.5 volts DC.

Maybe your O2 sensor is faulty.

[hippieman9]

Since everything seems to be working but your still holding steady dwell with the value you get with a cold or disconnected O2 sensor I think you have to see it that O2 signal is getting to the lambda ECU. Hard to tap into that sensor wire since it is shielded. Maybe you can pull the ECU connector cover off and be able to measure the voltage with every still hooked up.

Working lambda the sensor voltage should be 0.5 volts DC.

Maybe your O2 sensor is faulty.

I'll give it a try, It is a new Sensor, but could still be bad. if someone messed with the CO screw before how far would you have to turn it to get it back in? I have read the screw only turns a half turn and to adjust it 1/16" at a time.

[Bitsyncmaster]

I'll give it a try, It is a new Sensor, but could still be bad. if someone messed with the CO screw before how far would you have to turn it to get it back in? I have read the screw only turns a half turn and to adjust it 1/16" at a time.

Your getting the constant 45 deg dwell so it's not even reading the mixture. If you mixture was way off and the lambda was working you would get 10 deg constant or 85 deg constant.

[hippieman9]

Ok well for anyone interested in knowing the final results, I ended up removing the intake and installing all new seals, replaced the injector seals. Then started all over with setting the dwell. Upon getting the engine up to operating temp I found the dwell reading at 10° (doubled for 4cyl) I started to lean out the mixture and finally the dwell fell right into place. Apparently the mixture was set very rich! Probably someone compensating for an intake leak, which I discovered before removing the intake by spraying brake clean on the intake/block joint, and discovering that the engine would stumble and act like it wants to stall.
Thank you everyone for the input! I greatly appreciate it !