trouble starting when sitting while warm

[nissanconvert]

93 240 with 100k milesThis car starts beautifully all winter long and in the summer when it has been sitting and the engine is cold. It also starts fine for about 10 minutes after shutting it off on the hottest days after running on the freeway.

The problem is that after the engine is up to temp and it is a hot day, if i let her sit for more the 20 minutes or less then a few hours she is very stubborn to start if at all.

It cranks and catches always the first time but then chugs and shakes and loses control of the idle. If i do anything it dies. Give it gas, use the radio, turn on lights, put it in gear, anything. Sometimes it works itself out after a minute or two and runs fine. Sometimes(like today) it stalls out and then won't catch at all. It cranks a few times and then occasionally just clicks and does nothing. If I open the hood and let her cool down for about 15 minutes i get another good try of stumbling and eventually running.

Currently replaced the fuel and air filters.ECU gave knock sensor and o2 sensor codes which I ordered and are on the way but I doubt this is giving me starting issues, these are to correct the bogging during acceleration problems.Battery, starter and alternator tested good at autozone but on a cold day.Plugs are new and gapped correctly.Used different gas stations and grades to no avail.I've been told it might be gas vaporizing in the line but this sounds like baloney.

Any ideas as to what I might be trying to test?

[vancouverbc]

zerothread?id=254375
Modified by vancouverbc at 3:13 PM 5/31/2007

[nissanconvert]

No dice.I get .35kohms when fully warmed, .65 after about an hour and 2.3 when cold so its working fine.I just replaced the rotor and cap on the distributor because they were pretty corroded and original. Same problems but is now having trouble when under load, the motor is bogging down and rpms drop whenever i hit the gas on a hill.

[vancouverbc]

I dont know but you could check timing. Also,Disconnect O2 sensor to see if things improve.

Knock sensor info:

zerothread?id=253121

THere is a hard starting when warm article in my tutorial link in signature. Its not very good.

double check resistance between negative battery terminal and engine chasis. s/b less than 2ohms.

Your battery must be in bad shape from all the starting. check cables too.

check colour of spark. should not be orange.
Modified by vancouverbc at 2:21 PM 6/1/2007

[nissanconvert]

Ok I replaced the O2 sensor and knock sensor.It runs a lot better with more power but still had a starting issue again.It caught and then stumbled and died a few times before evening out.Also the computer threw a knock sensor code again,even after replacing it, is this a sign of a bad new sensor?

Battery resistance is good and timing is ok after checking. I'll check cables tomorrow.

[nissanconvert]

OK everything checks good that you suggested.I just checked the fuel pressure and i seem to only be getting 25 psi, is this the sign of a weak fuel pump or something?

[vancouverbc]

Not sure about that.

At idle, the pressure should be approximately:

235kPa / 2.4 kg/cm2 / 34 psi.

Disconnecting the vacuum hose, you should see:

294 kPa / 3.0 kg/cm2 / 43 psi.

[nissanconvert]

thats it! I replaced the fuel pump and it works great. no problems starting at all in high heat. Runs with oodles more power and no more hesitation.

[vancouverbc]

Good work:)