CIS Issue

[lsf911]

I have read a lot of posts here but none seem to describe my exact problem. Most posts are either cold start issues or warm start issues. Mine is neither, well more of a warm issue but not with starting.

Some back ground. I have an 83 SC (US) that I have owned for a couple of years now. The engine is stock 3.0 with the exception of the usual upgrade mods (i.e., chain tensioners, heat backdate, pop off valve, etc.). Engine always starts right up, whether it’s cold or warm.

The problem, rough warm idle for a short time, appears in 2 scenarios :

1) if the engine is warm, parked for a bit, then restarted, the car starts right up, but the idle will be low (500) and run rough for 5 minutes or so, then normal out.

2) if the ambient temperature is warm to hot, after normal engine cold startup, approximately 5 to 10 seconds later the idle drops to 500 rpm and will stall if no gas is applied. Again, after 5 minutes or so, the idle comes back up to normal (around 1000).

I do not have a fuel pressure gauge to take reading at this point. I am just looking for some thoughts to what parts I should be focusing on to test. I have done some reading on CIS and it seems there is a lot of component overlap so I am confused on where to start testing.

BTW, this problem has been with the car since I purchased it. I did check for vacuum leaks and I don't think I have any. At least not any that would be a problem. Removing the oil cap definitely drops the RPM's.

Any ideas? I appreciate your feedback.
Thanks.

[schumicat]

the place to start testing is fuel pressure, google jim CIS primer for some good info.

[tirwin]

More reading here:

CIS Troubleshooting for Dummies

The five minute time you mention is around the same time as it takes for the bimetallic strip in the WUR to warm up. A quick test there would be to make sure you are getting 12v at the electrical connection on the WUR with the key in the ON position (but not started). Also, the AAR uses a similar electrical connection/bimetallic strip to close it's valve. Without that happening, it would have to rely on engine heat to close off.

The thread I linked to above has a test for the AAR. I would do that and check the power to the WUR first since those are relatively easy to do. If that turns up nothing I would move on to the fuel pressures test.

[tirwin]

Edit. Duplicate post.

[lsf911]

tirwin,

Thanks for the tips. I will check out the voltages and do some more reading.

[Bob Kontak]

Originally Posted by lsf911

Any ideas? I appreciate your feedback.

Put a fat nail in the timing retard hose for fun.

Plugging the retard hose at the dist will give you a wee bit more advance at idle and that sometimes overcomes some of the "age" issues if the CIS components.

This assumes no false air leaks and all the other stuff mentioned is correct.

If it helps, still buy pressure gauges and perform some assurance work as there may be issues that are correctable that you are masking by a slight nudge in timing.

[lsf911]

I finally got a round to taking a couple of measurements.

With the WUR power connector unplugged, I turned the ignition to the on position (without starting the car) and measured power. I got a reading of 29 milli volts. I guess that is as close to zero as it gets.

I also measured the WUR resistance and got 9.4 ohms.

Both these measurements were taken with a warm engine. Not sure that matters or not.

Any suggestions?

Thanks.

[boyt911sc]

Originally Posted by lsf911

I finally got a round to taking a couple of measurements.

With the WUR power connector unplugged, I turned the ignition to the on position (without starting the car) and measured power. I got a reading of 29 milli volts. I guess that is as close to zero as it gets.

I also measured the WUR resistance and got 9.4 ohms.

Both these measurements were taken with a warm engine. Not sure that matters or not.

Any suggestions?

Thanks.

Lou,

Allow the car/engine to sit over-night and measure the WUR resistance. Or do at night when it is cooler. Do you have WUR-090 (0-438-140-090)? Without a fuel pressure gauge, there are so many things we assume to be good which complicates the troubleshooting process. Keep us posted.

Tony

[lsf911]

Tony,

Yes, I do have WUR-090. I will take the measurements again later tonight and report back.

Thanks!

[tirwin]

Lou,

I had to look back over the thread. I forgot to tell you that you'll have to jump the fuel pump relay. My bad. If you read the post in the Dummies thread I posted earlier, the instructions on how to test the fuel pressures are there and it covers how to jump the relay.

As Tony said the fuel pressures are the key test. I was just thinking that your symptoms seem like one of the components in the start up process isn't working correctly. Checking for power on the wiring harness for the WUR and the AAR is easy -- they are on the same circuit as the fuel pump -- but you'll have to jump the circuit to test it because it normally isn't energized until the car is started.

[lsf911]

Ah, that makes sense. I did read your CIS For Dummies. I should have picked up on that.
I did read somewhere that 9 ohms is out of adjustment for a WUR. Is that for a cold WUR?
Thanks for the help.

[Bob Kontak]

Believe 9 ohms is a little lean. Tony can confirm. In the high 20's for my 81 US WUR.

[boyt911sc]

Lou,

I could give you a loaner (WUR-090) and try it on your car. PM me if your are interested. Please do it quick because I'll be leaving for Carmel, CA this weekend and would be away for another 4 weeks.

There are couple of WUR-090's that I recently refurbished, tested and calibrated. All you have to do is mount it and connect the fuel line and electrical plug. PM sent.

Tony

[manbridge 74]

From my 74 owners manual... one must still pull up the hand throttle when engine is at operating temp. I'm assuming because a hot 4 stroke engine demands more air on restarting.

Not familiar with your year CIS, but perhaps you could try and start with gas pedal depressed some to see if starts are easier and to take into account a malfunctioning AAR valve etc.

[lsf911]

Tony,

Sent you a PM.

Bob and Manbridge, thanks for the replies.

I did measure the resistance again on the WUR this morning when it was cold. The resistance was the same, 9.4 ohms.

[jchris]

Lou, My 83 is doing exactly the same thing as yours was. I'm in the middle of tracking it down. Can I ask what ended up being the culprit?

Thanks,

Chris

[lsf911]

Chris,

Sorry to say, I am not sure yet. I put off the repair until Tony (boyt911sc) gets back from vacation.

Tony thinks it's my WUR. When he returns in September, he is going to loan me one to see if it fixes the problem.

I will certainly keep you in the loop with my results.

[boyt911sc]

Lou,

I'll be back home on the 27th of August to continue my unfinished work regarding this WUR loaner arrangements. I had two (2) overseas commitments that need to be tested multiple times before shipment. And one for South Carolina.

And a couple more awaiting for the arrival of the cores. PM sent regarding shipping address and other information. I've been very cautious lately because I have a successful unbroken streak with this exchange and wants to keep it going.

Tony

[jchris]

Lou, well I just timed my WUR warm up time. It went from a cold press of about 2 bar to warm press of 3.4 bar in about minute 10 seconds. I believe that is way too fast.

[lsf911]

That does seem fast. According to my Bentley manual chart, that's a temperature range of 57 to 93 degrees F in 10 seconds.

Hopefully one of the experts will chime in.