need help diagnosing why car did'nt start during hot day, but started 1st try later on at 10pm that night ?, the first thing i thought of was bad main relay ?

car is 90 crx si, 250,000 miles w/ ZC DOHC motor swapped in 2003, (estimated 140,000 miles on it about)

i was driving around during a hot day in stop and go traffic for couple hours, then i stopped at jack & the box right before i was almost home, when i left and went to start the car to leave, it did'nt start, i tried several times, it just did a "no crank, no start" thing, seeing the lights on the cluster, then i tried using a battery booster i have but it did'nt work cause was'nt charged up enough, then i got a jump off a guy in a truck parked next to us and tried couple times and did'nt do anything ?

so i locked the car up and walked home since it was only couple blocks away, and later on at 10pm i went back over there with some tools and stuff and look at it some more, and i tested the battery with a multi-meter and it said 12.78 volts, so looked good, then i tried starting it and it started the first time !!!, so i was glad it was'nt anything real problematic, and i drove to a couple places later and it still started fine each time, but i just want to figure out what caused it to not start so it does'nt happen again and leave me stranded in 100 degree heat like that ??? any thoughts what it could be ?

battery said 12.78 volts, and its around 2 years old, started is good and was rebuilt recently, alternator is 2 years old and have'nt had any alternator symptoms lately, connections are good on battery and starter and alt, cap/rotor new, new plugs, one thing i have'nt changed for a while is the main relay, might of been several years ago when the other one went bad and i put a new one in, so the current one could be going bad now maybe ? any thoughts on what else it could be ?

 

main relay forsure. us to have that issue with 2 efs i owned. only in summer. and cold cold days winter. u can fix it with solder youtube it or jus go grab a couple from junk yard. its located by hood latch behind the plastics its a bit tuff get to cuz a 10mm bolt holds it down but its do able with out removing much. i remember i did unbolt the hood latch tho another 2 10mm bolts good luck

 

could also be the igniter which is also affected by the heat - do you have any codes showing on the ECU, like maybe 15?

 

no i did'nt check the code on the ecu, even though i was meaning to do that, but i guess after seeing the car start 1st try, i just drove it home and did'nt worry about anything, but then later i realised i need to still find out the cause of why it did'nt start so it does'nt happen again and leave me stranded in 100 degree heat, so i will check the ecu for codes

i had my main relay unbolted from the mount bolt on the body and its been hanging down by the wires cause i was thinking i would unplug it as an easy cheap anti-theft device, but really have'nt done that once, but would it matter if the main relay is'nt bolted to the body like it should be ?, like does that ground it or anything important ?

 

I had the same problem. Replaced my main relay and its all good now. Mines was also hanging loose lol... but when I replaced it I placed it where it should be.

 

Sounds like a cracked solder joint on the main relay somewhere causing it not to get fuel. Its a common problem on EF's being that their 25+ years old. Give re-soldering a shot before you fork over cash for a new one. Worked for mine, its been running flawless since. The relay is located on the drivers side to the left of the fusebox. Little bit of a pain to get out but worth the time to fix! Heres a vid to help -

 

ok, i checked to see if i had an ECU code, and i did have a code 7, which is TPS (Throttle Position / Angle Sensor), and i read that it has to do with adjusting the fuel injectors according if its wide open throttle or closed throttle, etc..., and the O2 sensor corrects the mixture to match ..., so does'nt seem like that would have anything to do with why my car did'nt start after driving around long in the heat? would it?

i have a ZC DOHC motor, and i have heard a lot of them having damaged TPS sensors on them or misadjusted ones that you needed to mess with to make so it performs the best way it should, but i have never checked mine before.

it said to take hazard fuse out for 10 seconds from eng bay fusebox then start car and see if it still has a check engine light and the code on the ecu still ?, and if not, then could just be an intermittent problem, and test drive and see if shows it again, otherwise if it does still have check eng. light and code on ecu then says to unplug 3P connector from TPS and test the voltage to make sure its .5V at least.

if i end up needing one, it says the TPS from a crx si throttle body is the same as one for ZC.

 

would it be ok to drive my car to a couple stores this evening ? will it damage anything if i have a code 7 for the TPS sensor ?, or does it just affect only stuff like MPG or throttle & performance stuff? and not anything that damages and makes worse the more i drive it ?

 

i took the hazard fuse out 10 seconds, and started car, and check engine light was gone and ecu code was gone, which is good, but not sure if that means the TPS is ok or not ?, i mean car drives fine, but TPS is something hard to know if its good or not since it might just be affecting MPG or performance or whatever, cause not adjusted right or right voltage or damaged or need replacing, but i drove around all day in the heat and was in stop n go traffic jam on highway and car started every time and did'nt have check engine light or code again, but i guess maybe still worth testing the TPS voltage to just see what it reads.

 

I had the same, it might be main relay. I got it fixed for 5$ by a professional electrician.