cht sensor, need to change? Options

[nycchef]

73 1.7 idles @2000rpm and stalls every 15 minutes is back only now it has a re-epoxyed gas tank, tune up ,new filters, fuel pump has 12 volts and 34 psi at the fuel rail and still won,t run. been told i have to change the cht sensor but cannot reach it .is there a special tool or am i just one? hoping to finish car for less $ than a new 911. not as optimistic as i used to be need help!

[brp914]

20 yrs of djet experience tells me a cht wont cause your idle to double. sounds more like vacuum leaks and/or idle screw set too high, possibly combined with too advanced timing. a bad cht can cause intermittent stalling - thats what happened in my case. the way to verify is to put an ammeter in line with the cht, run the engine and wait. in my case, after a few minutes the engine would stall and simultaneously the current would drop to zero. good luck.

btw, if you replace the cht, depending on where you buy it, the hot/cold resistance values may be different and your engine may not idle well (it might hunt), so you may need to compensate with the mixture knob on the ecu.

[DNHunt]

Sounds like vacuum leaks to me too. A dead CHT makes it butt rich and it won't run. Been towed home cause of that one. Adjust the idle screw first then if it's still idling high look for vacuum leaks.

That tow job got me started on the path to Megasquirt because I felt the writing was on the wall and D-jet was obsolete. Maybe, maybe not!

In fact, I had a CHT come unplugged with MS and it was worse because it openned the injectors even longer than D-jet. It just put out the fire and I coasted to the side of the road. After a few cranks on the starter, the engine was locked and gas was pouring out of the exhaust. Luckily, I could walk home. Later I came back plugged the sensor in and drove it home

Dave

[ConeDodger]

73 1.7 idles @2000rpm and stalls every 15 minutes is back only now it has a re-epoxyed gas tank, tune up ,new filters, fuel pump has 12 volts and 34 psi at the fuel rail and still won,t run. been told i have to change the cht sensor but cannot reach it .is there a special tool or am i just one? hoping to finish car for less $ than a new 911. not as optimistic as i used to be need help!

I didn't read the previous thread but if I understand you correctly, your 1.7 runs fine for 15 minutes and then dies? If so, consider this possibility...

Your relay board could be heating up and expanding as the motor warms. Try another relay board.

If this works and it probably will not (murphy's law) I cannot take credit. I read it this morning in the Q&A at PCA national site... Ed Mayo's answer to someone with a similar problem.

[Cap'n Krusty]

34 PSI? That's a problem. 30 PSI is optimal, 29 works, 31 is questionable. A loose or bad CHT can cause intermittant stalling, as can a poor connection at the plug. I chased THAT particular gremlin for a while! Best get the valves, the dwell and timing, and the mixture set properly before you start looking for more exotic problems. TYhe Cap'n

[nycchef]

20 yrs of djet experience tells me a cht wont cause your idle to double. sounds more like vacuum leaks and/or idle screw set too high, possibly combined with too advanced timing. a bad cht can cause intermittent stalling - thats what happened in my case. the way to verify is to put an ammeter in line with the cht, run the engine and wait. in my case, after a few minutes the engine would stall and simultaneously the current would drop to zero. good luck.

btw, if you replace the cht, depending on where you buy it, the hot/cold resistance values may be different and your engine may not idle well (it might hunt), so you may need to compensate with the mixture knob on the ecu.

agree about the vacuum lines putting all new this week. car also tops out at 4000rpm that i think might be the cht

[rmital]

.is there a special tool

hey chef...yes there is....you just have to make it. I forget off hand what size socket it was, but found a lesser quality one in the pile, put it in a vice and sliced up the side with a grinding wheel. Easy if you got the tools to create the tool.....

I cut the old wire off the existing CHT, then removed.

Most IMPORTANT....put a couple drops of super glue on the copper washer and attach to the sensor so you don't drop it down into the engine tin. Then slide the wire up the slot, and feel you way into the cylinder head. I got lucky the first try and went in like a charm.

...let me know if you want me to ship my socket to ya...you could give it back at our first East Coast BBQ.

[Joe Owensby]

Once, I changed this sensor by using a deep well socket. I took an old extension (3/8 drive), and ground off a corner of it to allow the wire to come through the socket and out by the extension. I am just now rebuilding an old engine, and the sensor was permanently stuck in the head, and broke off. Now it has to be retapped.
Joe

[orthobiz]

I know this is an old thread but am curious about two points:

1. Is there only one CHT for all models? I have a 1974 1.8 liter
Part no: 0 280 130 017 ??

2. Where can I get a new CHT??

Thanks,

Paul

[r_towle]

Every chat is matched to the fi
,system you have. There are more than a few.

Pelican should have what you need.

[Dave_Darling]

Looks like they've all been superceded to one part number now. (IMG:style_emoticons/default/sad.gif)

The threads love to come out along with the sensor. Pain in the *ss to repair once that happens. I'd save that for a last resort.

--DD

[jim_hoyland]

What size socket ?

[BeatNavy]

13mm. I did what Mr. Owensby mentions in post #8.