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Discussion Starter #1
Hey all you folks so much smarter than me. In the last couple of days my spider's idling and running rough until engine gets up to temp.
It does idle, doesn't stall. When I press the accelerator it feels like it will stall then surges past this point and the engine runs fine. When trying to start off in first it hesitates and feels like it will stall, then the revs come up and it drives okay. It also seems to surge when under constant throttle. I'm driving with a steady throttle and the revs go up and the car goes faster.

After 4 or 5 minutes it smooths out and there is no problem.

Seems pretty clearly a "cold start" fuel delivery issue.
Any suggestions with what I should be looking at first?

Thanks
 

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Trained (ex)Professional, , 1953-2018 RIP,
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Not sure about the Motronic, but a shorted coolant temp sensor/sensor wiring can give that symptom in an L-Jet system. At the next cold start, try disconnecting the sensor to see if the symptom changes.
 

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Your symptoms are classic of a bad O2 sensor heater. The engine controller expects the sensor to be working properly at a certain time. Which it will with the help of a properly operating heater.

If the sensor is cold, it will read <.2V, and the Montronic will think that it's running lean, and will keep putting more fuel in until it reaches a clip. It will still run, just not too well....

And when you drive, you heat the sensor up with the exhaust stream, and it works ok.

I'd suggest replacing the O2 sensor- you can find a universal one at your local Bosch supply store- should be in the phone book.


Eric
 

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Question for Eric. My response was based on a GM ECM system which, in a cold start and for the first few minutes of running, is in open loop which ignores the input from the O2 sensor. Fuel delivery is based on a predetermined fuel map until the O2 sensor heats up and the system goes into closed loop. So the question is, does the Motronic system validate the O2 input in open loop?
The symptoms that Paradiso described sound to me like the engines running lean when cold. Could be wrong, though.
 

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Jim, the Motronic does ignore the sensor when it's open loop. Well, I would assume so, as all my experience is on another OEM system. But reading through the Bosch handbook, theirs and ours work the same, just like the GM one.

The real question is about time. I would expect a 91 Spider to go closed loop at about 40-50 seconds from a normal ambient start, not sure about a GM one.

I also factor in a little bit of odds- O2 sensor failure is pretty common, especially the heater. Temp sensors are very robust, since they are so simple. While it very well could be a number of sensors, the odds on favorite, to me, would be the sensor heater. Especially since the symptom goes away.

Eric
 

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Didn't know heated O2 sensors would go closed loop in less than a minute. That's much quicker than the unheated sensors I'm only slightly more familiar with. Knowing that O2 sensors are consumables, as opposed to the temp sensors, I'll change my mind and go with the O2 sensor (males are allowed to change their minds....aren't we?). ;)

Thanks for the education.
 

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I have state of the art hardware that is ready in 8 seconds. This just went into production on the '03 Focus PZEV.

Can't retrofit to old cars, though- requires a rather elaborate heater control to not burn it out.

Fun stuff...

Eric
 

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Discussion Starter #9
Thanks guys for the advice and for the opportunity to listen in while 2 guys who know what the heck they are talking about discuss the issue.

As soon as I get home from work I'll disconnect the temp sensor ( because its easy) and see what happens. I MIGHT get lucky.
Thanks again.
 

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Discussion Starter #10
All hail Papajam - Jim looks like you nailed it.
I got home, disconnected the sensor wire and taped it out of the way. Started the car up and it idles smoothly and exhibits none of the previous behavior. I pulled away with no hesitation whatsoever, smooth as silk.
Of course since its an Alfa, an hour from now I may need to replace the O2 sensor!

Dude, you are a genius.

Thanks

John
 

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Discussion Starter #12
So other than the fact that I have no temp gauge reading, what is the effect of having the sensor disconnected?
Is it that the ecu thinks that the car is up to temp as soon as it starts?
What does that mean in terms of fuel delivery?
Is it okay to drive around while I hunt down a Bosch temp sensor?

Please save me from my ignorance.
 

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Theoretically, the computer will use some base value if it sees some kind of fault. So it will run reasonably well, but not perfect.

On the Bosch manifold on my turbo car, there are 2 temp sensors- one for the dash and one for the compter, and they are really close to each other. Interesting that when you un-plug the computer sensor, the dash still works... Interesting that yours does not work that way.

Eric
 

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Discussion Starter #14
ACTUALLY - I realized that I had misunderstood and disconnected the dash gauge sender, not the bosch sensor. So now go figure!

Only thing that makes any sense is that Jim was right and that in finagling the dash sender plug loose I jostled the Bosch connection and that had the desired effect.

I plugged the dash gauge sender back in. Let's see what happens tomorrow morning when I go to start it up.

I'm so confused!
 

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Paradiso said:

...Dude, you are a genius.
Hardly! Your accurately described symptoms indicated (to me) a lean mixture. But I wouldn't do any backflips just yet; nor hunt down a temp sensor. By disconnecting the sensor, three things were tested; 1) the ECU went into fault (113 deg. F) and (apparently) richened up the mixture which cured the symptom, 2) the sensor to ECU wiring is OK and 3) the engines running lean at startup.
The closest Motronic specs I have at hand are for a '94 Saab 900 but I'd think that the principles of operation and the test specs would be very similar, if not the same.
To check the CTS, use a DVOM and note the resistance of the sensor at different engine temps. For example, at 77 deg. F, the resistance should be 2000 ohms; at 176 deg, 320 ohms. If the resistance doesn't change with engine temp, or it's zero or very low with a cold engine, then the sensor is NG. If the sensor tests OK, then something else is causing the lean condition.
To me, a vacuum leak would be the next place to look. A cracked hose, loose clamp or even a broken engine mount that stressed the MAF to plenum hose.
My though now is, although the O2 sensor may be bad, it is simply telling the ECU to richen up the mixture when it goes closed loop. However, if the heater in the O2 sensor is NG, then the system would take that much longer to go closed loop prolonging the symptoms you describe. If that's the case, then Eric's the genius! I've got virtually no experience with Motronic and I'm just reasoning this out! :p
Don't know why you lost the temp gauge though. I thought there were two temp sensors; one for the gauge and one for the ECU.
I wouldn't run too long with the sensor disconnected. O2 sensor and cat failure will result.
 

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Jim's right- when he started listing things that can go wrong. I'm sure both of us listed what, in our expereinces, would be the likely failure. But it may turn out to be something completely different.

IF you do go down the path of the O2 sensor, before changing parts, see if you can get an tool that pokes into wires to check their voltages. Then, start the car, and watch the sensor wire to engine signal while the engine is running badly. BTW, the wire to look at is the black one- the 2 white ones are the heater.

If its running rich and thinks that its lean, you'll see <.2V, the problem with that is if Jim is right, it will show that anyway.

Jim, I'd be pretty sure that your Saab's Motronic is virtually identical to the Spiders.

I wish I could help more, but I leave for the convention tomorrow morning, and will be away from the internet...

Eric
 

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Discussion Starter #17
Thanks guys.
Eric have a safe trip and lots of fun. I was planning on driving down but had to change plans.
Oh well, next year it'll be a 2 hr drive from my house!
 

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Discussion Starter #18
So I guess there are 2 possibilities:
1) I'm delusional and I hallucinated the rough running.
2) Jiggling the FI temp sensor connection was all that it took to fix this.

This morning the car started and idled smoothly, I gave it about 30 seconds to warm up and the engine responded smoothly to throttle.
 

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We'll bill ya!:D
Just kidding. There may have been some oil or road grime on the contacts and just moving the connector re-established contact. It probably wouldn't hurt to spray some electrical contact cleaner on all the FI connector plugs.
 

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Hmmm, sounds like my problem.

The only thing is, what is a "Motronic" and is it only found on SPICA models?

Was it on older spiders as well? A 74?
 
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