BLUE C2

My recently purchased 1989 C2 has a cold start / cold running problem. The car never starts from cold on the first attempt. It fires but doesn’t catch. Normally second or third go it keeps running. Once running the car idles fine at around 850 rpm but the revs flare and fall if the throttle is used whilst low speed manoeuvring and it is easy to stall. Blipping the throttle causes a hesitation. Once on the open road small amounts of throttle cause very jerky running, which only stops if the throttle is shut. Generous use of the throttle or none at all is the only way to progress without kangarooing down the road. Sometimes opening the throttle causes a big hesitation similar to not applying enough choke to an old Mini. After 2-3 minutes of driving everything sorts itself out and the car runs and drives perfectly. Warm / hot starts are also fine.
The car is standard apart from a cat bypass with the oxygen sensor removed and a jumper plug fitted in its place. I have checked the following:
Head temp sensor seems OK with 3000 Ohms at 25 degC and 200 Ohms after 3 minutes idling (80ish degC). Also the engine runs roughly when it is disconnected. I was convinced that this would be the problem but it seems to check out OK.
Idle switch has continuity at idle and open circuit when the throttle is opened. I also checked the full throttle switch and this is open circuit at idle and sometimes makes a circuit at full throttle. The switch works but only if I operate it manually. I’m assuming this won’t affect starting / cold running and has been put down as a job for later.
On the HT side the plugs are new as are the rotor arms, coils and the distributor caps. The engine runs on all six with either coil pack disconnected so again I assume all is well.
The battery and charging circuit all check out fine.
The air filter is clean as is the fuel filter.
My next line of investigation is the air mass flow meter.
Have I missed anything?
Please help me, as driving like it does when cold may give other road users a smile but I’m not happy with an otherwise wonderful car.

Ade - C4 91

This sounds like the problem I've had for about a year or so on my C4, and proved very difficult to track down. It really needs specialist too check everything systematically, but here's what I found.

Was up to about the same point you are (replaced coils, leads, rotors/caps, DME relay) in fact replaced just about everything electrical and then sent it to JZM.

They replaced the Air flow sensor (it was sticking). That improved driving when warm, but not idle when cold. Checked ISV - no fault found.
Checked Temp head sensor - no fault found.
Checked Battery - found high resistance on the earth lead - replaced. Also replaced the Transmission earth wire with a resulting minor improvement in stability. O2 Sensor was found to be slow and replaced which improved response.Air leaks - no fault found. They then swapped out the DME with no improvement.

Finally they checked the injectors and found one 1 faulty and all others other very dirty. They were replaced or cleaned. The car runs great.

So given what I know now, I'd work the other way round - check injectors and ground wires first. then start on the Airflow sensor etc.

Good luck.

Ade.

johnfm

G'day Blue

WHy is the O2 sensor 'jumpered'?? My cat bypass has the sensor still in place. Not sure how the DME meters fuel on cold starts, but I would presume it runs closed loop & needs the data from the O2 sensor??

I would try givig Steve Weiner an e-mail (look for him in the archives or find him at <a href="http://www.rennsportsystems.com" target="_blank">www.rennsportsystems.com</a>

Christer

John

What he means is that his DME is jumpered. Mine is as I no longer have a CAT so I don't need an O2 sensor either. What 'Blue' should check is that he has an altitude sensor installed - apparently there is quite a bit of difference even between relatively small changes in elevation.

I don't know that much about O2 sensors, but I know that they don't work until they get to a temperature of about 600 fahrenheit (or nice ansd warm anyway), therefore they do not contribute at all when the car is started from cold.

johnfm

Why would you bypass the O2 sensor in the first place??

Ade - C4 91

I've never understood why some decat solutions use a Alt. sensor either. How can an altitude sensor compensate for mixture adjustment due to combustion burn rate conditions?

Ade.

DaveK

When I had my cat bypass fitted, it originally had O2 sensor. When I later had the car chipped by JZM they recomended getting rid of it - which I did. They basically said that the purpose of the O2 sensor was primarily to protect the cat from over-fuelling - see how many cars you can find that have an O2 sensor but no cat. Hence, their argument was that it placed some artifical restrictions on the fuelling which I didn't need anymore. No idea if this is true, but I don't seem to have lost anything by getting rid of it.

As for Alt. sensor - I'm sure it can't cope with that and it's primarily so that you can still drive up mountains (not that I do that often).

I guess than on a flat road, my alt. sensor would not change it's output. I wonder how much an O2 sensor would?

Andy Roe

I may be wrong, but just a theory...does the O2 Sensor measure Oxygen content? Wouldn't the Atl. Sensor do the same - ie. the higher you go, the less "O2" there is in the air?

DaveK

I think that's the idea. But I guess Ade's point is that the oxygen content (as measured at the exhaust) is dependent on more than just altitude, so the O2 sensor can cope with all of the variables.

Christer

No, the altitude sensor does not measure oxygen content - I know that much. I don't know how it works though, perhaps the same way as a Casio watch does?

JZ Machtech seem to be the people to ask. Now that Dave mentions it they also told me that that the main reason for the O2 sensor was to protect the CAT, in my case the O2 sensor was going bad anyway so it was a 'no-brainer' for me. One jumpers the DME to use different maps without the restrictive O2 sensor.

DaveK

I don't think Andy was saying it measured oxygen content directly. Just that the higher you go, the less oxygen is in the air - hence it can provide the same function if it has some kind of mapping table between altitude and O2 content. I'd assumed this was basically what it does.

Are you saying it definitely doesn't do this? (Or are you saying you didn't read Andy's comment properly......) <img border="0" title="" alt="[Wink]" src="wink.gif" />

johnfm

Calling all blind men....calling all blind men....

I think Christer hit the nail on the head here...talk to Jonas at JZM, he is very very helpful & knows a lot more than we do!!

Christer

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by DaveK:
<strong>Are you saying it definitely doesn't do this? (Or are you saying you didn't read Andy's comment properly......) <img border="0" title="" alt="[Wink]" src="wink.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I seem to remember JZM explaining its actual function at which point my eyes glazed over. I am 90% sure it does not measure actual oxygen content though - I would have remembered that.

I third my own advice which was duly seconded by John, speak to JZ Machtech if you really want to know.

Dave, I never misread posts. People mis-write them.

Ade - C4 91

Firstly - I agree that Jonas is very knowledgeable, but I really wanted to hear some technical knowledge from someone who doesn't have a financially vested interest (with all respect to JZM).

Secondly - I do know there are some very knowledgeable people on this board (some with electrical/mechanical engineering degrees in engine management for example)..so where are you all...answer the questions damn you...

I guess what I'm saying is that removing the O2 Sensor just doesn't make any sense.

My understanding is that main purpose of the O2 sensor is not to protect the Cat (although that maybe a side effect of it's function), it's to provide feed back to determine the burn effectiveness of the cycle (determine the enrichment on the next cycle). The DME will try to get the burn as lean as possible (as close to the mappings optimal values) without causing the mixture to go too lean.

So if you remove the O2 sensor what do you get?
For a start - no feed back! Your engine can run lean or rich and it wouldn't know. The only detection would be the knock sensors telling it the engine is pinging if too lean under load. You are simply basing the enrichment on the predetermined values in the mapping - plus an adjustment for altitude if fitted.

Ade.

BLUE C2

The oxygen sensor removal and cat by-pass were fitted before I bought the car so I cannot say what difference this made to the way the car ran. However as the O2 sensor takes some time to heat up (even with the heater coil) so I can’t see that it will have any affect on cold starting or the initial period of cold running as the engine will run “on the map” until the O2 sensor reaches operating temperature.
Catalysts only work efficiently over a narrow air / fuel ratio hence the need for a closed loop system. As the cat also needs to be hot to “light off” (start working), the delay whilst waiting for the O2 sensor to warm up is not a problem.
The altitude sensor is almost certainly just an absolute pressure sensor and used to correct for the reduced air density at altitude. But as the engine uses an air mass flow meter surely some level of compensation will take place anyway as the reduced air density will give a smaller flow meter reading for a given throttle opening / engine speed. At altitude it may just be that the resolution of the flow meter is too wide to cope and hence the need for extra compensation be it from an O2 sensor or pressure sensor.
My area of experience is on race engine management systems where the main inputs are load (throttle position and rate of change) engine speed / position and temperature (engine and air). The ambient pressure input is used to compensate fuelling and ignition for air density changes from the “as mapped” values (due to altitude / weather) and air box pressure recovery at speed, which can be substantial on a well developed air box. Wide range lambda sensors are used to monitor air / fuel ratio and can be used closed loop but tend to give laggy throttle response in the car.

Ade, thanks for the pointers on earth leads, which I’ll follow up. The cleaning and flow / pattern testing of the fuel injectors is also on my list of things to try but in my experience dirty / low flowing injectors usually give problems with hot and cold engines and my problem is only when cold. I will also check out the ISV.
Thanks
Blue C2