question on cylinder head temp sensor

[rnln]

I have had an intermittent starting problem (twisted the key and nothing happens, while voltage is ok). I read a lot about the starter solenoid and starter relay. A while back, I replaced the starter, battery, alternator, etc. Problem is lessen but is still there once in a while. Most of the times, it happened after a long idle such as after a smog check, or an AC recharge. Sometimes it happed after several cold starts.

A friend went to my place a while ago. We chat on many problem we discussed on the board. I told him about this and he pointed right at the cylinder head temp sensor after listening to my explanation (my car ran great when he was there). He was pretty sure about it. He also found that my CHTS is a single wire.

Is it possible to test it? And how? Is it a “maybe”, or is it a “definitely” the problem so just spend $75 bucks and a day under the car?

Mine is a Carrera, engine is 1988. Is this the 2 wires one I should get? 930-606-915-00-M14. It has 2 photos. One is
http://www.pelicanparts.com/cgi-bin/smart/imgdsply.cgi?pn=93060691500-M14
and one is


Thanks in advance.

[ianc]

If the engine does not turn over at all when you turn they key, then the CHT is not the problem. A bad CHT would prevent the engine from starting\running well, but the engine would still crank. My guess would be a dodgy ignition switch.

ianc

[ZOA NOM]

Originally Posted by ianc

My guess would be a dodgy ignition switch.

+1

The ignition switch is a wear item. Think of how many times it has to perform it's function.

[rnln]

If it's the ignition switch, then it should heppend "whenever it wants". My problem happen only in 2 situation. 1- when it's really hot after a LONG LONG idle. 2- sometimes it happend after many starts.
Also, it is happening right now. I went under the seat and hold the fuel pump relay (main relay?) in my hand while starting the car, I can hear/feel the relay click. It is cold, not hot. Also something else is moving while twisting the key, sounds like a fan somewhere in the hood.
Do you still think it's the ignition switch?

edited:
ok, 2 people think it's the switch. Then to test it, I can hot jump the wire right? If I supply the yellw wire with some 12v, without twisting the key, I would activate the starter. Am I correct. Let me come out and try it right now. Will report.

Back:
It can not be the ignition switch. I measure the voltage at the mid size yellow wire underneath it. It got voltage (almost 12v). I remember now that I did measure it many times when it happend and it always got the same voltage. Before I replace the starter, it happen more often that I had to keep the voltage meter in the car to make sure voltage go through this wire.
I play with the main relay a little more careful and found that it click when the key twisted once, and click again when key at start position. So look like the ignition key is ok to me.

I also tried different things with the alarm while starting the car, such as at unarm, arm, door open, door closed, etc. without help.
Any other things I can look into?

[ianc]

Do you still think it's the ignition switch?

I don't know if it's the switch or not, but if the engine does not crank, one thing is is NOT is the CHTS.

If it's happening right now, get under the car, pull the wire off the solenoid and check it for juice while your wife cranks with the key. You should see voltage there, and with the wire on, the solenoid should click. If it does, then the starter may not be getting enough juice for any number of reasons.

Take a look at the wiring diagrams here and be sure the ignition switch is actually passing current to where it's supposed to for your year when the key is in the 'start' position. That should get you pointed in the right direction at least,

ianc

[yelcab1]

Either the ignition switch, or your starter. Was it a rebuilt one, or brand new one? One in a while you get a rebuilt one with a bent shaft so that the slider gear does not slide out when it is HOT. Yes, it happened to me.

[rnln]

ianc,
Thanks for the hint on the CHTS. One thing to filter out.

Yelcab1,
oh man... this is a disappointment. I just replaced it and this task is hell

Time to get under the car again. Will be back.
Note: no wonder wives hate old car. We were getting to go somewhere before I realized it won't start.

[yelcab1]

Originally Posted by rnln

ianc,
Thanks for the hint on the CHTS. One thing to filter out.

Yelcab1,
oh man... this is a disappointment. I just replaced it and this task is hell

Time to get under the car again. Will be back.
Note: no wonder wives hate old car. We were getting to go somewhere before I realized it won't start.

Yes, the starter is hell on a G50 tranny. You do a partial drop right? You also need some funky tools, which I have learned to have.

[ZOA NOM]

You never mentioned replacing the DME relay. Did you do that FIRST?

[yelcab1]

Originally Posted by rnln

Note: no wonder wives hate old car. We were getting to go somewhere before I realized it won't start.

No worries, you can always have her push the car, it will start.

[rnln]

Yelcab1,
yes, the shop did partial drop. I couldn't do without droping the tranny, for 2 days on the lift. Well, 5 hours today well worth it. When she came out and asked if I need help, I am done and cleaning up :lol:

Zoanas,
oh on the relay. I didn't replace it. Some nights reading the board, I took it off and opened it up. Resoldered all the points and nothing change. Once in a while, I also touch it after the drive, both when it happen and when it not happening, and it's not that extreme hot. It's normal.

Thanks you so much. Problem finally found and temporary solved after over a year searching and replacing. The magic words you guys were saying were "FOR SURE it is either the ignition switch or the starter". That makes sense to me too but after too long and too much searching and replacing, my mind must got out of the loop.
I finally got under the car with the feeling of hating the car, but finally found that the voltage on the yellow wire was only 7v+, while it is carrying 11v+ under the dash. Second test was jumping a long wire from the starter solenoid to the engine bay:
1- Got all the wire ready to jump a 12v+ from engine bay to the starter's solenoid.
2- start the car with key, no start. To make sure the problem is still there.
3- jump a 12+v to this wire,
Result was VROOOOM. Problem found.

In the past, the problem was when it happend, it always happend when you are on the road. There is no way to get under the car. I know and plan to connect a wire to the engine bay to measure it when it happen but I thought I would rather replace the starter first, since it's too old anyway. But when the old starter came out, it still look good. Another thing that made me feel lazy to connect connect the solenoid wire to the engine bay is because the yellow wire at the dash always carry 11v+. I never thought one wire can have 11v+ at one end and 7v+ at the other end.

Thank you so much. It's my good day, instead of a bad day as I thought. Now time for the wife and kid to go christmas shopping. Again, thanks.

[ZOA NOM]

I still recommend you replace the DME relay, and keep the one you re-soldered as a spare. Congratulations on finding your problem.

[rnln]

This is the second recommendation on this, must be a reason. Will do, when I need to order something from PP, I will add it to the order. Thanks.
Today, I am so happy because of this.
Now my mind is (and will be) busy thinking of the best/safe way to run a bigger wire from starter to engine bay, and to the front cabin.

[yelcab1]

Originally Posted by rnln

Now my mind is (and will be) busy thinking of the best/safe way to run a bigger wire from starter to engine bay, and to the front cabin.

Are you saying your yellow wire is the problem? That it carries 11V at one end, and drops to 7V at the other when there is a big current going through?

[RoninLB]

my car's yellow wire from switch had a Y connector tucked under dash going to the AC and to starter solenoid. All connectors have voltage drops.

Then there is the aftermarket alarm starter kill that inserts another voltage drop.

A hot starter solenoid could draw much more amps than when it's cold.

I installed 10 ga yellow wire from solenoid up along alternator wire, going to starter, into engine compartment. Cole Hersee sells a large current momentary on switch.

New 8 ga from starter switch to starter is in the future.

I'd say the easiest way to determine if you have a wiring problem is a starter jump test when problem happens. No matter, an engine comp starter momentary on switch is worth the time to install.

[rick-l]

Originally Posted by ZOANAS

I still recommend you replace the DME relay, and keep the one you re-soldered as a spare. Congratulations on finding your problem.

Since you are familiar with how the DME relay functions and have repaired the fatigued metal joints I don't see the advantage of buying another relay.

[ianc]

One other bit of maintenance to do while you're in there is to remove the engine\transmission ground strap from the body of the car, clean it, and replace it. On a G50 car, it is on the passenger's side, forward of the sway bar near the front of the transmission. You can have all the voltage you like to the yellow solenoid wire, but if it has a poor ground, it won't work...

ianc

[Jascha]

Great communal fix…

It seems you were at the threshold (~7.5V) of what it would take to get the solenoid energized.

You might want to check the ‘yellow wire’ going to the A/C system and heater/blower control unit (‘87-‘89 models) in case that one of these circuits pulls-down the ignition switch (terminal 50) supply voltage that splits-off @ [starter terminal 50] to these two circuits


(I just checked the circuit diagram to confirm that to be the case)

[rnln]

yelcab1,
yess. 11v+ at the dash and 7v+ at the stater while twisting the key. At the starter, I measured it many times while twisting the key to make sure and everytime, it's only 7v+.

Jascha,
Just in case, do you know where the splits are? Under tha dash, in the trunk where some AC components are, or in engine bay?

One more general question. Does any one know what is the required voltage to activate the general purpose relay, term 86? I am thinking of adding a relay on the yellow wire between the engine and the starter. In case when it happen, 7v+ will activate the realy to draw 12v from battery to the stater solenoid.

Thanks guys.

[Ned, NYNA11]

rnin,
From the ignition switch the yellow wire goes through a plugin connector in the firewall. I found the plug had backed out and that gave a bad connection on the yellow wire.