I have a 1990 Honda Civic. I have been having this odd intermittent starting problem for a year now. It ONLY has difficulty starting when the weather is hot. In the morning, everning/night, and during the fall/winter it starts like a champ, on the first crank every time. But during the hottest parts of the day it just won't. It sounds like it wants to but just doesn't. Now if I wait 30 minutes or so and try again it starts normally.

I have gotten a tune up, changed the fuel filter, air filter, flushed the radiator, and checked the battery but the problem persists in this very predictible way. I read from someone else's post that for many Hondas the main relay is the culprit so last weekend I bought a new main relay from the auto parts store. Much to my dismay, the starting problem persists.

What am I not thinking of?? What else could pose such a specific problem--starting problems during the hottest part of the day only, reliably starts 30 minutes after first attempt, never a problem at night or during winter?

Here's some additional info. I'm not certain it's truly related or a red herring. Now what I've also noticed is that my power door locks do not work during the day as well but work perfectly fine at night after sunset. I had hitherto ignored it because I assumed they were apples and oranges. The starting problem behaves for all the world like a Main Relay problem but after having replaced it I've had to do some extra thinking....I wonder if it's possible for there to be a POST-relay problem, i.e. there is a circuit or harness which is shared by the power lock and Main Relay. If this can occur it may explain why the problem seems so much like a Main Relay problem. Although possible, I doubt the stars were so misaligned that I bought a defective Main Relay too. LOL. I sure would love to hear what you guys have to contribute about this problem. (Btw, I have already checked all the fuses).

Well I'm hitting myself right now. Just discovered that I DID NOT replace the main relay a week ago. I replaced the 'fuel pump relay'. I placed myself at the mercy of the auto store...since I didn't know what the main relay looked like I asked them for one and then found the identical part in my car and swapped them out. If it wasn't for a bit of fortune I may have gone on thinking I replaced the right part. Well ok, I'll keep an eye on the car now and let you guys know if all is well.