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N* 4.9L


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I have a 2004 SRX V8 N* 4.6L and am having very bad MPG, around 9-10MPG. I suspect a bad Fuel Injector on cyl #5 as it is very loud. If I disconnect #5 injector the tapping goes away.

I have a very good scan tool that lets me see the output voltage of all 4 O2 sensors. What I'd like to do if force the engine control system into open-loop so I can run a few tests and I don't want things in closed-loop because I'm looking for mixture readings from the RHS vs LHS O2 sensors without any adjustments being done by closed-loop mode.

Is there any cheap easy trick to put the ECU into open-loop? just for testing. and I want all 4 O2 sensors still connected. Would disconnecting some simple sensor (like the MAF) force open-loop? My scan tool tells me if I'm in open or closed loop so should be easy to verify.

Thanks.

Edited by sal.carceller@cox.net
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Sal, my guess is that by disconnecting the coolant temp sensor, the system will detect a cold engine and not go into closed loop, but that is just a guess, I would test that, Mike

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

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Here is its location

04SRXECTsensor.gif

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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The engine control module (ECM) controls all ignition system functions, and constantly corrects the basic spark timing. The ECM monitors information from various sensor inputs that include the following:

The throttle position (TP) sensor

The engine coolant temperature (ECT) sensor

The mass air flow (MAF) sensor

The intake air temperature (IAT) sensor

The vehicle speed sensor (VSS)

The transmission gear position or range information sensors

The engine knock sensor (KS)

The Run Mode has 2 conditions: Open Loop operation and Closed Loop operation. When the engine is first started and the engine speed is above 480 RPM, the system goes into an Open Loop operation. In an Open Loop operation, the engine control module (ECM) ignores the signals from the oxygen sensors and calculates the required injector pulse width based primarily on inputs from the mass air flow (MAF), intake air temperature (IAT), and engine coolant temperatures (ECT) sensors.

In a Closed Loop, the ECM adjusts the calculated injector pulse width for each bank of injectors based on the signals from each oxygen sensor

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I found this in "Scan Tool Output Controls"

Loop Status

Output Controls

This function changes to loop status. The commanded states include Open and Closed. When commanded Open or Closed, the system remains in the commanded state until cancelled by the scan tool.

It seems that a scan tool can command OPEN LOOP

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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On the 4.6L engine the injectors should be between 11 and 14 ohms resistance

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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First, I have no codes set at all. But MPG is real bad.

All injectors measure 12-12.5 ohms

Unplugging each injector one at a time confirms each cyl is firing. Each unplug sets appropriate code for engine mis-fire.

Took plugs out to inspect them and found cyl #7 (Passenger side rear) looks real bad. Here's a picture.

post-2721-1263758942_thumb.jpg

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OK, if you are not getting codes, you are not misfiring which is good.

Check your fuel pressure, we have had members complain of poor gas mileage with a pump putting out lower than spec pressure

Is it possible that you lost the platinum pad off of a few plugs? This plug looks like its fouled, how about the coil, putting out a weak spark?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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First thing I tested was FP it seems fine and in spec. Spec says 55-60PSI engine not running FP on.

I read 60PSI fully pressurized engine off.

It reads 65PSI at idle.

I'm going to simply get new plugs to start with. Hopefully this helps.

Will also do quick test for intake air leaks (Smoke Test).

Here's another pic of all the plugs on that side.

post-2721-1263759925_thumb.jpg

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I can't really zoom in too close but from where I am sitting those plugs look pretty bad, what is their gap compared to spec?, any real large gaps?, I find that if I lose a platinum pad, the gap is huge

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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