Fubu6913

So i have had my 92 RS v6 5speed for around a year or so, two weeks ago the fuel pump died. After replacing the fuel pump the car starts and idles fine but has no power under load. The ECM seems to be working yet its not giving me any codes idicating an error. It does give codes when certain sensors are dissconnected so im assuming the ecm isnt bad. When i ground the aldl with the engine running it tells me its in open loop mode...
now fuel pressure checked good after the pump change, the car starts and idles fine.
ive changed the O2 sensor, the IAT sensor, dist cap and rotor and the ign coil with little to no improvement. I have reset the ecm several times and it still seems to be stuck in open loop.... Need some advice please

PaulyC

O2 needs to be up to temp, coolant temp sensor needs to be above 150 degrees (roughly 575 ohms or less read on the sensor) and engine running for 2.5 minutes for closed loop mode. Personally I would suspect a coolant temp sensor or circuit, its the usual suspect in this situation.

Fubu6913

Thank you for the reply.
although we did check the CTS before, we did pull it out and due proper resistance test in hot water and observed the sensor operating correctly. I am getting 5v at the cts connector. Im not sure how to test if the ecm is receiving the info correctly. Also not sure how to check the o2 sensor for proper operation,although it was replaced. Thanks again for the help this problem has me stumped and can use all the advice available.

RBob

iTrader: (1)

Scan tool.

RBob.

jeffas000073

Purchase a ALDL cable that connects the OBD1 ALDL port to a USB port on your laptop computer. You can get them from several different places for about $60. Don't waste a lot of time trying to find one cheaper since they are all about the same price (unless you want to make one). Here is the first one I found on Ebay:

https://www.ebay.com/i/121938262168?chn=ps

Then download Tunerpro RT software (free, but it's suggested you donate) which will tell you all sorts of things that are going on with your ECM/Ignition/Sensors/Engine:

http://www.tunerpro.net/downloadApp.htm

These are the best two things you can start with that will begin to tell you what's going on with your car.

Have fun!!

Fubu6913

Thanks alot for the info.. Will be getting that adapter ordered in the morning. Curious if its worth the extra for the bluetooth adapter from 1320 electronics or just stick with the wired one?

Fubu6913

Ok... So used a Bosch scan tool at oreillys this w eekend and everything seemed to be operating correctly from the little bit it showed me.. The ecu is switching back and forth between closed loop and open loop, yet only after the o2 sensor read above 560mV. Yet at idle with the engine at temperature the O2 is only reading around 420mV. This is a new O2 sensor. Not sure if the little info i got was helpful or not. In process of aquiring a proper scan cord. Will update with any changes.. Thanks again

PaulyC

Ok so the 420 is approximately the ECU reference (450mv) and is used when started cold or idling and when/if the sensor is cools below 600deg but it cant be there too long; no more than one minute after the engine has been running for 2-2.5 minutes I believe. So long as you are not setting a code 13 that should be fine. You should see that voltage vary from above 600mv to below 300mv when it is up to temp so what you are seeing is a bit low. Again however if you are not setting a code it is probably functioning ok and maybe the scanner wasn't showing it or you weren't watching for voltage over time. Have another look while somebody is driving if you want to verify the sensor operation and verify closed loop during driving conditions.

Fubu6913

So assuming the ecu, and sensors are operating correctly, what are some mechanical issues that would cause the rich conditition without throwing codes?

PaulyC

If everything monitoring the system is functioning properly and you had something causing a rich condition you would know about it. Lets say you had a leaky injector just dumping fuel. If the sensors and ECU were functioning the O2 sensor would signal the functioning ECU and it would do its best to correct the situation and when it could not it would set a code. Similar with something like a vacuum leak. A severe lean condition could result but the functioning O2 sensor would see it and the functioning ECU would try to correct it and if not be able to do so and set a code.

Are you experiencing this now?

Fubu6913

Im still not getting any codes coming up,the engine idles fine, revs slower then it should in neutral. Out driving there is very little power and takes way to long to get the rpms up. There are no misfires or stumbling. No backfires. The ecu does store codes if i pull a sensor plug. It doesn't seem to be showing any telltale symptoms. Never had this issue before the fuel pump quit.

PaulyC

That sounds like more of a timing thing but since you just changed the pump you should verify fuel pressure just to make sure that problem is corrected. I don't have the exact pressure numbers for a 3.1 but i believe you should see 40-47 psi at the prime and idling in the 30-37 range, basically a 10psi or so drop when engine is idling.

Fubu6913

It does seem like a timing issue, base timing is set at 10, the ecu does control the timing with the Est plug connected. Watching the timing mark as i rev the engine it seems a little rough in spots. But does advance and retard with the throttle. What could be causing timing trouble thats not thowing a code or causing a misfire?

jeffas000073

Fubu6913

drove the car around last night with the fuel pressure gauge hooked up to the fuel rail. The gauge showed 42psi at prime and it dropped down to 37-38psi at idle. In gear on acceleration it would rise to 45-47psi. Seemed to be a slight fluctuation of 2-3psi around 3k rpms.

GeneralDisorder

iTrader: (1)

That would be about normal fuel pressure for GM's.

GD