m103 W124 coolant temp sensor error for CIS

[89-300ce]

1989 300ce
I'm trying to chase down a warm start issue. Starts fine cold. Starts fine fully hot. Won't start if I shut it down before it gets fully hot. If I let it cool down again it starts no problem. Runs fine otherwise.

I've checked the CIS temp sensor and it seems to read low
ie. @ 23C it reads 3.5kohm instead of 2.5kohm so it reads for approx. 10C
@ 80C it reads 0.650kohm instead of 0.325kohm so it reads for approx. 60C

Are these readings in the range of acceptable error or would they be enough for a warm start problem?
I believe at 80C CIS goes to closed loop and no longer uses enriched start. If the ECU thinks that coolant temp is 60C and it actually is 80C would it use enriched start and create my warm start problem?

Thanks
Jorg

[optimusprime]

Could be is yours a twin temp sensor or a three pin ? remove the plug on the top and start your engine. Could be a number of items that will give you this problem . Only thing i can think of is if you can try is another ht coil . Might be the ht system - plugs - distributor cap, or rotor arm . Its an hard one and a bit like my problem .Replaced everything other than pumps - 2 on the m103 .I need to do a fuel pressure test .It starts fine cold but when its hot it starts and stops right away .But it will always start and run fine after that .

[89-300ce]

It's the two pin sensor, green with red o-rings near the firewall. When it won't start it never starts. It might backfire if I give it full throttle but it won't start until it cools down again.

[Frank Reiner]

89:

Try this as a test of mixture:
Remove air cleaner
Bring engine to the "warm"/no start temperature
Cycle the fuel pump 2 or 3 times (key to on, listen for pump run/stop, key off, key on again, etc.)
Press down on air flow sensor plate ~ 1/2"
Hear fuel squeal through metering valve and injection valves?
Try starting

If the engine starts, the basic adjustment is lean. The basic adjustment is done with the screw between the air flow sensor and the fuel distributor.

[89-300ce]

Frank,
I'll give this a try. Is the screw you are talking about the allen head that's adjusted to get a zero amp reading at the EHA in closed loop?

Jorg

[Frank Reiner]

Originally Posted by 89-300ce

Frank,
I'll give this a try. Is the screw you are talking about the allen head that's adjusted to get a zero amp reading at the EHA in closed loop? Jorg

Yes, it's in a tower, and is spring loaded. 3mm hex driver, push down and turn a bit until you feel the spring loaded piece engage the actual adjusting screw. No more than 1/8 turn at a time. CW=rich. Make adjustments with engine stopped, then re-start.

[Duke2.6]

Originally Posted by 89-300ce

1989 300ce
I'm trying to chase down a warm start issue. Starts fine cold. Starts fine fully hot. Won't start if I shut it down before it gets fully hot. If I let it cool down again it starts no problem. Runs fine otherwise.

I've checked the CIS temp sensor and it seems to read low
ie. @ 23C it reads 3.5kohm instead of 2.5kohm so it reads for approx. 10C
@ 80C it reads 0.650kohm instead of 0.325kohm so it reads for approx. 60C

Are these readings in the range of acceptable error or would they be enough for a warm start problem?
I believe at 80C CIS goes to closed loop and no longer uses enriched start. If the ECU thinks that coolant temp is 60C and it actually is 80C would it use enriched start and create my warm start problem?

Thanks
Jorg

I'm pretty sure the KE system goes into closed loop at 60C coolant temperature. Also I don't recommend messing with the mixture adjustment unless you do it "by the book" looking at duty cycle. There was a good writeup here years ago. Try a search with the words landiss duty cycle.

I've also experienced longer than usual cranking when the engine is "warm". I found that once the engine is cranking if I press the throttle about a quarter to half down it starts much quicker.

Duke

[89-300ce]

FYI

So I replaced the temp sensor with no improvement.

Performance deteriorated to the point that the car would stall if I sat at a red light for more than a few minutes and then would not restart until cold again. The car ran fine at speed. I tried running some injector cleaner though the car thinking that an injector was dribbling at idle and loading up the engine. No improvement.

In desperation I installed a new O2 sensor and problem solved. The sensor I replaced was still sending signal and I had the mixture set with the EHA amp method. I guess the sensor had gone out of calibration. It was covered in soot.

I must say that I drive the car very little and it will sit for 6 months at a time (with fuel treatment). I will often start the car and idle it to operating temperature just to keep things lubricated. The car had gone through periods of similar poor performance before but always improved once it had been driven enough. Not this time.


Jorg

[Duke2.6]

Originally Posted by 89-300ce

FYI



I must say that I drive the car very little and it will sit for 6 months at a time (with fuel treatment). I will often start the car and idle it to operating temperature just to keep things lubricated.
Jorg

I've been storing cars including my '88 190E 5-speed for six to eighteen months for over 30 years. Prior to storage I fill the fuel tank, change the oil, set TP at or near the maximum placarded on the sidewall and may change the brake fluid and/or antifreeze if they expire prior to the end of storage.

Once they're asleep, I NEVER start them, and on those that have modern FI systems I cycle the key several time prior to cranking to pressurize the fuel system. Then they start right up, and the oil pressure comes up within a second or two.

This question comes up a lot in the vintage Corvette community since guys in most climates store their cars during the winter, and I and others who are retired automotive engineers give the same advice.

Duke

[89-300ce]

Thanks Duke,

Coming from you that's good enough for me.

Jorg

[Air&Road]

Don’t stop your testing with the sensor. You need to verify the entire circuit.

[89-300ce]

Originally Posted by Air&Road

Don’t stop your testing with the sensor. You need to verify the entire circuit.

I'm not sure I understand. The closed loop seems to now be working as expected. What else should I be looking at?

Jorg

[optimusprime]

I have this same problem .And i have replaced everything in the ht system also fuel injectors seals o rings sensors filter accumulator only thing now is fuel pressure .What points me in this direction is on the day i reoplaced the injectors i forgot to release fuel pressure and removing the hard line to injector i found that no fuel came out .This told me it was low on pressure . The car is in staorage now untill March ,,then soon after i get the car back then it will let me check the fuel pressure,. My M103 has twin pumps i am now thinking that one is not doing its job or fuel is returning via the non return valve .

[Diseasel300]

Originally Posted by optimusprime

I have this same problem .And i have replaced everything in the ht system also fuel injectors seals o rings sensors filter accumulator only thing now is fuel pressure .What points me in this direction is on the day i reoplaced the injectors i forgot to release fuel pressure and removing the hard line to injector i found that no fuel came out .This told me it was low on pressure . The car is in staorage now untill March ,,then soon after i get the car back then it will let me check the fuel pressure,. My M103 has twin pumps i am now thinking that one is not doing its job or fuel is returning via the non return valve .

CIS injectors pop at something like 10-15PSI, which is very low pressure. There shouldn't really be much of anything stored in the hard lines since after the pintle pops, pressure in the line drops below that of the pop pressure. The pressure line that should be storing pressure is the incoming fuel line to the fuel distributor from the fuel pump(s). Don't go chasing a problem that doesn't exist.