1996 240sx: Intermittant Startup problems - Shudder and failure

[offtheline]

My car for the most part has run well recently. It starts up and idles at 1000 rpms for a minute or two and then drops down to about 800 a bit later.

However, twice now my car has refused to start altogether. It is very odd and I will explain the circumstances each time:

1. I had left school after a rain storm and my car started up just fine. I drove to a friend's house on the highway with absolutely no problems at all. When I got to the house, I shut it off. A while later when I attempted to turn it back on, the car turned over but then would die quickly. It would shudder and slowly the revs would drop from ~500 down to 200 and then it would just die. The response varied in how many seconds it would take until it died, and sometimes it would not turn over at all. If I gave it gas while it was on, it would immediately die, so I couldn't rev it up at all. I spent some time checking the vacuum lines and the connectors, but nothing seemed loose or disconnected. So, I called a tow truck to have him tow it to my apt for a closer look. When he arrived, he said that he'd seen this before and he told me that he would lift the rear end of my car up in the air and bang on the gas tank with a wrench while I tried to start it. I thought, "this guy is crazy, but Okay." So we did just that and the car started up to my surprise. He left and my car ran well except for a puff of white smoke that came out after I started it the next two or three times.

Jump forward to this morning (4-5 weeks later) :2. I go to buy a burrito and when I get back in my car, the same thing happens. It barely turns over and when it does, the car just dies almost immediately. So, in an attempt to replicate the tow truck scenario, I jack up the rear end of my car and ask a guy nearby to knock on the fuel lines and gas tank while I start it.... No dice. It wouldn't budge. After more tries of various things, the car wouldn't even turn over. It would only grind the ignition. After sitting there for a while, eating my buritto and buying one for the homeless guy that tried to help me, I decided to try a few things. While the car was off, I just opened the throttle a few times manually where the cable connects to the metal piece. I tried starting it and VOILA. It worked. I did notice some moisture coming out of the exhaust though.

So what gives? I assumed all along that it was an aging fuel pump. I thought maybe somehow it was being flooded or wasn't getting enough fuel. But then why would opening and closing the throttle make any difference?

Any ideas?

BTW: I searched and didn't come up with anything

Modified by offtheline at 11:11 PM 10/7/2006
Modified by offtheline at 11:25 PM 10/7/2006

[rogoman]

It seems that you may have a fuel delivery problem.

If you haven't replaced the fuel filter, it should be replaced because the filter may be plugged up causing your problem.

An easy way to test the fuel pump and filter is to disconnect the fuel hose from the top of the fuel filter and insert a long length of spare hose into the top of the fuel filter with the other end draped over the fender going into a catch can placed on the ground. Now turn the ignition key to the run position but DO NOT START THE ENGINE. You should see fuel going into the can at a good rate for several seconds.

Also consider installing a tempory fuel pressure tee'd into the line coming off the top of the fuel filter. The pressure reading should be around 34 psi.