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Spi Cold-start Idling Issue


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#1 Avl_Paul

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Posted 28 December 2007 - 01:56 PM

Hello Group,

I just purchased a 1995 Mini Cooper (Silverbullet special edition) and am finding it has a cold-start idle issue. I see that there is a ton of Pinned info on the SPI's which I am now crawling through. I was wondering if anyone could give a me a tip where to start the troubleshooting to minimize the number of things I have to go through.

The problem statement:
Engine runs fine once warm and idles well. After letting the engine cool down in 45-55 Deg F weather, I tried starting it. It would start but splutter and sometimes stall out. If I throttled it at all, it would stall. I tried starting numerous times and it kept dying every time I throttled. Finally, I let it rough idle for a while to warm up and then threw it in gear rapidly. Once under load, it took off.

I'm guessing it may be an issue with the "idle heater relay?" I assume there is an idle air control vavle also (stepper motor) - maybe I need to reset that?

Previous owner had little mechanical ability and just kept this thing garaged for the occasional Sunday drive. I'm betting he is going to tell me that he hever started it in the cold! He did mention it would idle a little funny at first when cold but I suspected a bit of a pulsing/wavering in speed...not dying..

Hey if anyone has a diagnostic tool in the States - drop me a line. I may want to "rent" one in the future.

Thanks for the help folks.
-Paul

#2 Sprocket

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Posted 28 December 2007 - 02:28 PM

What a coincidence, seriously! I have spoken to another US member via PM and he is having pretty much the same problems

Might be worth you two getting together and purchasing a Diagnostic code reader. The user is mogg and the link to his profile is here http://www.theminifo...?showuser=15908

I will suggest similar things. If the problem is only cold start, it may be down to the Manifold heater. This is the circular device in the base of the inlet manifold. This is an NTC heater element, as temperature rises, the resistance rises, so its self regulating. The ECU switches it off at a pre determined coolant temperature. These are known to be problematic. The connection onto the heater can burn out due to a loose connection. The relay pack PCB track can and does burn out, you can open the relay pack and see if there is any damage.

There is a possability that the stepper motor is not operating as it should. I have found that the motors themselves are usualy very reliable. Its the solder connections of the wiring onto the motor that the problem.

Ensure there are no air leaks on the Vacuum line that connects the ECU to the manifold, this will give the biggest error in MAP readings.

There is a slim possability that the Lambda sensor heater relay may have failed, swap the two yellow relays on the bulkhead for each other and see if it makes a difference, if it does, replace the relay on the left, that will now be the faulty relay and on the cooling fan circuit.

Other than that, I would be wanting to connect the diagnostic to actualy see what the ECU is thinking.

Hope that helps

One thing that could be compounding the issue, the more I think about it, is the coolant temp sensor. When these start to fail the fail low, the temperature reading starts to drift.

#3 Avl_Paul

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Posted 28 December 2007 - 11:17 PM

Thanks for the feedback. I did a quick check of the vaccuum tubes and they looked good - will try to do a more thorough check tonight. I swapped the two yellow relays and there was no change. In fact, I removed both and there was still no change! Does that make any sense? Some additional pieces of info that may help explain things:

1) It is idling relatively well when I start it but it dies the instant I push on the accelerator. On the other hand, if I throttle it under the hood (manually opening the throttle), it will throttle up much better!?!? Does that make any sense to anyone? It will start to hesistate and then immeidately respond if I manually throttle it under the hood. Seems like it should perform the same either way.

2) I discovered that it has a small coolant leak (previous owner claims he hasn't seen coolant leaking in 2 yrs). When I checked the coolant reservoir, it was down ~ 1-2 inches or a quart or so. I'm really surprised I didn't overheat on the drive home yesterday! Could this be related? Could explain your theory on the coolant temp sensor although I can't see how that sensor affects cold start conditions since the coolant should be at the same temp as ambient.

I really held off buying an SPI for just the reason that I knew a diagnostic tool would be hard to come by in the States. Now, I'm in that situation within 1 day of owning one.

-P

#4 elvisthepizzaman

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Posted 29 December 2007 - 12:13 AM

the coolant temperature sensor tells the ecu how cold or hot the coolant is. If its cold the ecu will activate its cold startup procedure and adjust the stepper motor to a predetermined point and as the motor warms up the ecu will read from the sensor and adjust your idle accordingly so the coolant sensor has everything to do with cold startup.

#5 Avl_Paul

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Posted 29 December 2007 - 12:29 AM

the coolant temperature sensor tells the ecu how cold or hot the coolant is. If its cold the ecu will activate its cold startup procedure and adjust the stepper motor to a predetermined point and as the motor warms up the ecu will read from the sensor and adjust your idle accordingly so the coolant sensor has everything to do with cold startup.


Man, Elvis, there really are sightings of you everywhere! Here and MiniMania (and you give good input in both locations). Thanks.

#6 Sprocket

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Posted 29 December 2007 - 01:08 AM

If the actual coolant temp is 42 degrees F, but the sensor is telling the ECU that it is 28 degrees F, the ECU will add more fuel than is actualy required on warm up. Infact when the engine is warm, the ECU may still run in warm up mode and run rich.

Check the manifold heater connections, the heater is responsible for heating up the air entering the engine to help prevent the fuel condensing out on the inlet tract.

There is one possability, but i have only ever experienced it in all conditions, not just cold start and warm up. There is a Rover buletin that describes a problem with the Vacuum sensing line to the ECU. This can become liquid locked with fuel. This affects the MAP sensor inside the ECU and cand give symptoms you describe. What needs to be done, you need to remove the ECU from the car, screw up a piece of cotton wool, small enough to insert it into Vacuum sensing port on the ECU no more than about an inch to an inch and a half. Place the ECU with the vac sensing port downwards ontop of a warm radiator, or in a warm place. Leave it overnight. Before you refit the ECU, remove the Black vacuum lines, check carefully the elbow ends, no splits whatso ever, and blow them through. Check the fuel trap is also clear, thats the black rectangular box thing on the left of the inlet manifold.

Failing this, without a code reader, all I can suggest is replace parts until it sorts the problem. Unfortunately on injection systems that have been neglected, it is more often than not, a combination of several faults rather than just one.

Start with the usual maintenance items, plugs, leads, dizy cap, rotor arm, air filter, then the next likely suspect is the coolant temp sensor, as this is one of the major components to control the fueling.

Then the Air temp sensor, this alters fueling in relation to the density of the air, this is only changes fueling slightly, but if its totaly open circuit, it could be reading -40 degrees centigrade and that is a fair change in fueling.

Manifold heater resistance should be quite low when cold, and almost infinity when above 50 degrees Centigrade. Dont forget to check the connection and the relay pack.

Stepper motor, when the engine is warm, rev the engine from the engine bay and let thenthrottle snap back, watch the plunger of the stepper motor, it should catch the throttle and move it back to idle position almost straight away, if it almost stops before idle and then returns to idle after, or, it moves past idle and then extends again, the stepper is out of adjustment. Again check the stepper motor wire connections on the motor itself, you will have to remove it from the housing.

Lambda sensor, has been described how to test and is now a pinned topic, have a look in the pinned section

Throttle position sensors do fail, but that would be the same for a warm engine.

Make sure the coolant thermostat is an 88 degree Centigrade item.

Check the general tune of the engine, Rocker clearancies, compression test. Dont rule out mechanical issues.

The ECU should be the VERY last thing that you ever consider as the fault if everything else has been PROVEN to be satisfactory. The ECUs are very robust and only really fail when they have had a dead short.

Oh and is the ECU a one plug or two plug version?

Theres a bit to be getting on with there. :thumbsup:

Its something simple, it usualy is.




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