95 Metro Test SW Affect On Timing

[sas95]

I am setting the timing on my 1995 Geo Metro 3-cylinder. I just completed installing a low-mileage replacement engine.

When I jumper the Test SW terminal to ground in the Duty Check Data Link Connector (with the car warmed up and running), the ignition timing does not change. It is showing steady at 8 degrees with my timing light.

Should I expect the timing to change or drop? Should the timing change when the jumper is connected?

I am worried the jumpering is not working and don't know how to find out if it is or not. I observe the timing advance when I increase the throttle by hand, with jumper and without jumper.

Thanks for any info.

[GM Line Rat]

Just set the timing per instructions..... Engine off, insert the jumper, connect a timing light, mark the timing marks with a piece of white chaulk or paint marker, loosen the hold down bolts for the distrbutor, start the engine. Check the timing and set it per instructions in you manual. Turn engine off, tighten dist bolts, recheck the timing...if it's still on the mark, turn the engine off, remove the jumper and your done!....The engine timing will advance when the engine speed increases......This is normal. The timing should not change or flucuate while idling and while your setting it unless you move the distributor to adjust it. Just set the timing per instructions in your manual.

[sas95]

Thanks for your reply, but see below for the ignition timing procedure out of my 1995 Geo Metro OEM Service Manual. Why does it say to verify advance with engine speed in the last step? Why is there the notice in step 8?

--- Verbatim ---------------------------
1. Start and run engine until normal operating temperature is attained.
2. Stop engine, but keep ignition switch in the "ON" position for 5 seconds, then start engine again.
3. Run engine at 2,000 RPM for 5 minutes and then keep it running at idle speed.
4. Make sure that: all electrical loads (wipers, radio, headlights, defogger and blower) are "OFF", A/C is "OFF," if equipped, Gearshift control lever is set to neutral, parking brake is fully engaged.
5. Check to be sure that idle speed is within specification.
6. Connect a timing light to No. 1 secondary (spark plug) wire.
7. Remove cap from Duty Check Data Link Connector (DLC); located next to the left strut tower.
8. Connect a fused jumper from Duty Check DLC cavity "4" to cavity "5" so that ignition timing is fixed.
NOTICE: In this state, ignition timing is fixed.
9. Check timing. It should be 5 degrees +/- 1 degree at specified idle. Refer to "Vehicle Emission Control Information Label".
10. If not within specification, loosen distributor flange bolts and rotate distributor and repeat until timing is within specifications.
11. Remove jumper from Duty Check DLC and make sure that the timing advances according to engine speed.
------------------------------

[91Caprice9c1]

Originally Posted by sas95

I am setting the timing on my 1995 Geo Metro 3-cylinder. I just completed installing a low-mileage replacement engine.

When I jumper the Test SW terminal to ground in the Duty Check Data Link Connector (with the car warmed up and running), the ignition timing does not change. It is showing steady at 8 degrees with my timing light.

Should I expect the timing to change or drop? Should the timing change when the jumper is connected?

I am worried the jumpering is not working and don't know how to find out if it is or not. I observe the timing advance when I increase the throttle by hand, with jumper and without jumper.

Thanks for any info.

In a perfect world, the timing should fluctuate a bit and be somewhere around 10-12° BTDC with NO jumper attached while monitoring with a timing light. What then is suppose to happen is that you attach a jumper to said connector in order to stop the pcm from adjusting timing via input sensors so that you can set base timing. So this much we understand, which is why you are confused. It has been my experience with a fleet of 22 metros (model years 93-2000) that some of them do not respond when the jumper is attached, much how you are describing, accept I have been UNABLE to STOP the PCM from Adjusting timing. That is, after I attach the jumper, the timing still fluctuates normally, and the jumper has no effect. This lead me to believe that a possible open circuit existed and I did not pursue it any further until an important discovery I made one day revealed to me that I could achieve the same result (get the pcm to STOP adjusting timing, so that I could set Base timing) by simply unplugging the electrical connector to the MAP sensor located on the passenger side firewall near the top of the engine compartment which attaches to a vacuum port at the base of the Throttle Body. You seem to have the opposite problem, either A) you have a short in the DLC circuit that keeps the car in diagnostic mode constantly B) You have a disconnected or non-fucntional sensor (which is essentially what I did by disconnecting the MAP sensor; forcing it into open loop operation - in which the PCM refers to programmed tables, instead of responding to information fed to it by the input sensors), bad grounds or a faulty pcm. What is your fuel mileage like? Is your check engine light on? Check for loose or disconnected sensors (ECT and MAP primarily) check your sensor grounds at the back of the Throttle Body, and if you are handy with a wiring diagram and an ohm meter (Digital Multimeter ONLY!!) you can check to see if maybe you have a short in the Diagnostic circuit. Goodluck and report back.

-MechanicMatt

[sas95]

91Caprice9c1,
Thank you for you thoughtful response. Your experience with multiple Geos is quite valuable. I will plan to unplug the MAP sensor connector tomorrow, watching the timing as I do. Will get back to you with results.

[95OLDSGA]

Hello, This is my first post and I am not familiar with navagating around the site yet but I need to know what the rotation of a Geo Metro 4 cyl engine is.
If I am standing by the right front tire and face the belts (engine front), what direction are the belts turning? CW or CCW.
If you are curious I have a complete A/C unit from one (serpentine belt) that I want to modify and install on my VW Air Cooled.
Thanks, Marvin

[91Caprice9c1]

The engine rotates clockwise, toward the front of the car.

[95OLDSGA]

Thank you,
Marvin

[sas95]

91Caprice9c1,
I pulled the MAP sensor elec. connector as you described, and it worked! The timing dropped down instantly. I set my base timing to 5 degrees, then plugged the connector back in and the timing jumped up into the teens or 20's. With MAP sens. conn. pulled out, the engine rpm also dropped to just a few hundred. I had to twist the throttle by hand to increase it back up. I didn't have a tach reading of the engine, so did it by ear, based on the sound of the engine at normal idle. Not as accurate but I think it sufficed.

To answer your other questions, yes, I have been having a recurring DTC 51 - EGR malfunction. I've spent a lot of time checking the electrical, vacuum and mechanical aspects of the EGR system. They all check out OK. By accident yesterday I may have solved the problem. The battery neg. cable was lose easier then before. I couldn't tighten it down enough, so I went to AutoZone and got a replacement cable. Installed it and went for a 20-mile test drive. The MIL never came on! The MIL had been coming on after driving at highway speeds for a while. I figuring now that it may have been engine and road vibration enough to create inermittent ground faults, but still enough to provide all the other systems adequate power. My manual says the ECM turns OFF and then ON again the EGR SV and watches for a MAP sensor change. If the change isn't large enough, DTC 51 is triggered. Suspecting ground faults interrupted this process.

I haven't been measuring my mileage yet. Will now start to do so.

Thanks again for your help.

sas95

[91Caprice9c1]

Glad it worked for ya. If the ground cable contact was able to support the load of the starting system, I would not expect it to be causing a specific system fault. I assume you removed the EGR from the intake manifold, and inspected the passages for carbon build up? You ought to get to the bottom of your EGR issue ASAP, as neglecting this system can result in burned and broken valves and/or piston damage, not to mention excessive NOx emissions!

MechanicMatt

Originally Posted by sas95

91Caprice9c1,
I pulled the MAP sensor elec. connector as you described, and it worked! The timing dropped down instantly. I set my base timing to 5 degrees, then plugged the connector back in and the timing jumped up into the teens or 20's. With MAP sens. conn. pulled out, the engine rpm also dropped to just a few hundred. I had to twist the throttle by hand to increase it back up. I didn't have a tach reading of the engine, so did it by ear, based on the sound of the engine at normal idle. Not as accurate but I think it sufficed.

To answer your other questions, yes, I have been having a recurring DTC 51 - EGR malfunction. I've spent a lot of time checking the electrical, vacuum and mechanical aspects of the EGR system. They all check out OK. By accident yesterday I may have solved the problem. The battery neg. cable was lose easier then before. I couldn't tighten it down enough, so I went to AutoZone and got a replacement cable. Installed it and went for a 20-mile test drive. The MIL never came on! The MIL had been coming on after driving at highway speeds for a while. I figuring now that it may have been engine and road vibration enough to create inermittent ground faults, but still enough to provide all the other systems adequate power. My manual says the ECM turns OFF and then ON again the EGR SV and watches for a MAP sensor change. If the change isn't large enough, DTC 51 is triggered. Suspecting ground faults interrupted this process.

I haven't been measuring my mileage yet. Will now start to do so.

Thanks again for your help.

sas95

[sas95]

I read the wikipedia page on Geo Metros just after I bought my Metro back in January, where it warned of EGR problems damaging the engine. I compression- tested the engine: left 190, middle 135, right 190psi. And, it was loosing oil. The center cylinder was shot. The check engine light was on with DTC 51. Subsequently I decided to buy a low mileage replacement engine and installed it myself. Reused the existing intake and exhaust manifolds.

I cleaned out the exhaust passage in the intake manifold - it was alsmost completely clogged. Cleaned out corresponding passage in the exh. manifold. I inspected the exhaust transfer passage in the engine block. It looked OK so didn't try to clean it. I cleaned out the EGR valve, itself and tested operation with a vacuum pump and gauge, blowing air through it all the while . I tested the EGR solenoid valve (EGR SV) and EGR pressure transducer for proper operation. Also followed the EGR electrical circuit fault tree with multimeter and jumper wires. Seems to be all working.

Upon reading what DoctorBill in this forum did to clean his passages, I may go back and repeat his procedure if I run into problems or have the intake manifold off for any reason.

The only behavior that seems out of place is EGR operation with cold engine. My OEM manual says the EGR system should not operate until the engine coolant temperature has come up. I can start up my car with a cold engine, wait 5 or 10 seconds, then open the throttle with my hand and watch the EGR valve open when the engine revs up. (I verified the EGR SV does not open with conditions: engine off, ignition on.)

Have you seen this on any of your Metros?

[91Caprice9c1]

Originally Posted by sas95

I read the wikipedia page on Geo Metros just after I bought my Metro back in January, where it warned of EGR problems damaging the engine.

The EGR system on these cars often stops functioning due to carbon build-up, which then results in high combustion temperatures, which results in burned exhaust valves or broken exhaust valves which end up finding their way into the piston. While an over-active EGR system will cause driveability problems (stalling, rough idle, lack of power) it will not cause the engine damage associated with an EGR system which has stopped functioning.

Originally Posted by sas95

The only behavior that seems out of place is EGR operation with cold engine. My OEM manual says the EGR system should not operate until the engine coolant temperature has come up. I can start up my car with a cold engine, wait 5 or 10 seconds, then open the throttle with my hand and watch the EGR valve open when the engine revs up. (I verified the EGR SV does not open with conditions: engine off, ignition on.)

EGR should not operate with a cold engine. The purpose of EGR is to cool combustion temperatures to reduce emissions. Specifically, oxides of nitrogen (NOx) which form when nitrogen and oxygen from the atmosphere combine in the combustion process. Since nitrogen and oxygen are a fairly odd couple, they only combine under extreme heat/pressure, such as is found in the combustion chamber. A 'cold' engine is cool enough to keep NOx low enough to not warrant the use of EGR which would otherwise hinder the perfect combustion that is aspired for. I would suspect first and foremost that your ECT (coolant temp sensor) is to blame, the computer may very well be under the impression that you've got a warm or even hot engine when in reality it's cold. Your temp gauge uses a seperate single wire thermosistor that is independent of the two, three wire coolant temp sensors used by the ECM to interpret engine temperature. This will generally cause poor driveability either at cold start, or after the engine has reached operating temperature, but there is a gray area that the sensor may be feeding to the computer, which may not have a severe impact on performance. I would backprobe both ECT's (one at the outlet, and one mounted in the throttle body) and compare to spec.

-MechanicMatt

[sas95]

Wow! Two engine temperature sensors! I'm shocked, amazed, ... dissapointed. I will do some measurements with my Fluke for resistance of the two sensors - cold/ambient, and then with warm engine. If the engine ECT circuit is not working properly, it will affect fuel injector operation, I think. Not good.

One other bit of information that might be perplexing: as the engine is warming up, and when the engine temperature gauge in the instrument panel shows about 3/5's the way up from C to H, the radiator cooling fan turns on. The gauge drops down 1/2 and the fan turns off. And then cycle repeats with time, as one would expect.

Does this draw suspicion away from the ECT circuit?

Thanks for the explanation of EGR function. I may not have metioned I only have between 50 - 100 miles on the car since I replaced the engine and cleaned out the EGR passage ways. Also verified EGR valve operation with it off the intake manifold by blowing in the exhaust inlet hole while increasing vacuum to the diaphram with a vacuum pump.

Will still keep in mind your warnings about the importance of the EGR system.

[91Caprice9c1]

Originally Posted by sas95

If the engine ECT circuit is not working properly, it will affect fuel injector operation, I think. Not good.

Indeed, the ECT(s), IAT, O2 and MAP sensors are the big reporters for the ECM, which uses the data from these specific sensors in order to adjust fuel injector pulse width/duty cycle, or the amount of time the injector stays open.

Originally Posted by sas95

One other bit of information that might be perplexing: as the engine is warming up, and when the engine temperature gauge in the instrument panel shows about 3/5's the way up from C to H, the radiator cooling fan turns on. The gauge drops down 1/2 and the fan turns off. And then cycle repeats with time, as one would expect.

Does this draw suspicion away from the ECT circuit?

Well, this does appear to be pretty normal operation. Which would tell us that the ECM knows when to turn the fan on and off, which would conflict with the theory that our premature EGR operation is due to a faulty ECT. Unless (and I do not know for sure) one ECT is used for fan cycling and the other is used for fuel trim and other control parameters, such as EGR operation. I do know that not all of my metros have two ECTs, but the couple I know for sure have two ECTs are OBDI vehicles (like yours), and once when diagnosing a driveability problem, it was when I unplugged the ECT at the TB that the driveability problem went away. When an ECT is disconnected that is responsible for fan cycling, the ECM should turn the fan on immediately by default for reasons of self-preservation. If you disconnect one of the ECTs and the fan does not turn on automatically, but disconnecting the other ECT does turn on the fan, then we know that the duties between the two are indeed divided and we can continue to suspect a faulty ECT as a culprit for the improper EGR operation.

-MechanicMatt

[sas95]

Follow-up report on my ECTs. I'm confident the ECT mounted in the thermostat housing is the one used by the ECM, and the other temperature sensor is used simply for the instrument panel gauge. I studied the schematics in my repair manual closer to come to this conclusion.

When I unplug the ECT connector, (with engine running), the radiator fan immediately turns on. Plugh the connector back in the fan turns off.

I questioned my ealier assertion about EGR valve operating with cold engine. I let the car rest over night, went out in the morning, and with the hood up, started the engine, and immediatedly ran around to the fron of the car. Let it idle for 5 to 10 seconds, then revved the engine way up. The EGR valve did not open. After maybe 30 seconds of engine runnging, the thermostat housing was hot to the touch. I revved the engine again and the EGR valve opened.

Turned the engine off, unplugged the ECT connector, measured the resistance at about 280 ohms. This is about 180 deg. F. from the chart in my repair manual. Earlier I had measured the resistance with the engine cooled overnight, and it was about 1700 ohms - about 80 deg. F. This is making more sense now. I think the ECT circuits are working properly.

What I am concluding now is that the coolant in the thermostat takes hours to cool down enough to drop below the threshold in the ECM for EGR operation. This is with outdoor temperature in the 70's/80's and strong sun.

And for the timing ... I had set the timing using your suggestion of removing the MAP sensor connector, but gauged the engine rpm by ear to what it was with the MAP sensor plugged in. I'm looking at buying a Vetronix Tech I scanner on eBay, which should give RPM, along with many other ECM parameters. Will reset the timing then.

Thanks again for all your help.