300ZX (Z31) Performance / Technical Discussions related to Turbo charging, Supercharging, Engine, ECU, exhaust, and etc. performance enhancements and Techical related.

Fun with the CHTS

Old 10-13-2016, 10:03 AM
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Join Date: Apr 2015
Location: Iowa
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Fun with the CHTS

Last spring I had a strange "warm start" issue, where the car would start hot or cold but not when it had run for 5 minutes or so. I replaced the FPR and a most of the vac hoses at that time and this seemed to fix the problem. The car ran great for the next 16 months, so well in fact that when I had the timing belt changed I didn't do the CHTS. Big mistake, less that 4K miles after the timing belt job the warm start issue returns and quickly morphs into a hot start issue too. After the car would warm up the only way to get it to start is to pull the fuel pump fuse, otherwise is massively floods out, cold start is never a problem. This isn't usually a CHTS problem according to what I read nearly everywhere I looked, so I check the other likely suspects.
All of the other stuff is working fine, no codes on the ECU, no leaky vac lines. I dig into the EF & EC section of the FSM and the only other system related part is the CHTS, I check and it OHMs out as no resistance. I hadn't heard of the 1987 models with the "fail safe to full rich" settings on the ECU this sounds like it might be my problem. So I'm going to change the CHTS. The part is only $18.00, that and 3 hours of my life.
I used the "CHTS the easy way" method from Z31.com, basically it is spot on other than the following changes. If you have A/C installed on the car you need to remove the bracket for the A/C belt tensioner pulley. It is completely in the way of everything you have to do. Second, once you find the CHTS down there shove a rag into the gap between the block and the back side of the timing belt cover. I dropped the new CHTS while trying to thread it and then spent the next 45 minutes getting it out of the 5" deep hole behind the timing belt cover. That sucked. Last, always buy the new connector assembly when you go to do the job. Mine was fried (like 1/2 melted off) and it cost me 40 minutes running to the parts store to get the CHTS plug end and another 20 to rebuild the harness.
Lots of descriptions make this job sound like a nightmare but really it isn't so bad. Other than losing the new CHTS into the gap of death (pack it off with a rag, I'm serious) nothing was all that difficult. The Z31 has run for a week now and both warm and hot start issues have gone away completely. I also think that I will get better gas mileage since the car isn't fail safe to full rich.
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