Hard Start When Hot

[stocker2000]

Hi all.

2000 Altima, 110K km (68K miles). My problem is just like the title says;. If the car sits overnight, or at least long enough to reach ambient temperature, it seems to start just fine. If I then drive around and bring it up to temperature, stop the car for a few minutes (say long enough to go grab a coffee), and then start it:

a) the engine takes longer to crank, andb) the engine stumbles for a second like it's not getting enough fuel or air or something, shaking the whole car; I hear this "thrumping" noise, which I could swear is something bouncing off of the underside of the hood, as the engine shakes violently beneath.

Despite these theatrics, it has always started on the first turn of the key.I checked, and I have no stored codes on the ECU.

Here's what I have done so far:

1) Replaced spark plugs. Checked wires and distriutor cap and rotor. OK2) Fuel filter was replaced recentlyand air filter cleaned (it's a K&N).2) Battery is only about 5 months old.3) Replaced ECT sensor with new & checked voltage at harness. OK4) Checked IAT sensor resistance at various temperatures (using my freezer and a hair dryer) and checked voltage at the harness. OK

I'm not sure what else to check, so I'm posting here for ideas. I've been trying to do a lot more of my own work on my car lately, and have been enjoying it. I just don't have the troubleshooting expertise yet.

Any help is appreciated.

[NISTECH]

The K&N oiled air filter is known to cause air flow meter problems when over oiled so besure that filter is pretty dry, A properly oiled filter should not glisten when bright light is shined on it.

You say you checked your cap? Where was the cap made? should have a stamp somewhere on it either inside or out.

[stocker2000]

You were right about the filter; I did over-oil it last time I cleaned it. The "clean" side of the airbox looked like it had some oil staining around the wire mesh, and the bottom of the airbox on the dirty side was pooling filter oil. So, yeah, I'll lighten up on the oil when I next get a chance to clean it.

In the meantime, I put in a standard OEM filter I had lying around.

So, what's the best way to rid the MAF of the oily film? Or does it need to be replaced?

I didn't get around to checking the cap for it's manufacturing location. How does that make a difference?
Modified by stocker2000 at 10:16 PM 4/18/2005

[NISTECH]

Guys on here metion cleaning it with carb clean or brake clean, I dont endorse it as i havent done it myself, But they mention they had success with it so its up to you if you want to try before you go out and buy one.

On the distributor cap if its made in italy it will likely cause internal cap arching under load. It is very common with the italy made cap.

[stocker2000]

Researched cleaning the MAF a little. Not surprisingly, there are those who say go ahead and do it, and others who don't dare since it's such a delicate piece of eqiupment (and very expensive too).

I'll have to try to test it before I go fooking it up or dishing out the money for a new one.

Some other possibilities I was thinking of as for the cause of my problem:

- idle air control valve blockage,- injectors that need cleaning.

What do you think about those?

[NISTECH]

I dont think its your idle air control valve since hard starts from that usually show them selves on a cold start up. If it were the injectors it would not be just a hot thing.

The noise under the hood when it does start I am interpiting as intake poping due to a lean misfire condition. How does it run after the engine stabilizes after it goes through its theatrics?

[stocker2000]

The noise sounds is more like a thud, which at first I thought the engine was bouncing off the underside of the hood. And I have enough vibration in the car to suspect that the engine is moving a little much on the mounts. I did have my mounts checked by a mechanic very recently, and they said that there was no unusual amount of play.

After start-up, the engine stabilizes almost immediately; the "theatrics" last only seconds (for now). In general, the car runs just fine, but my fuel economy is slightly lower than normal, and I have a slight loss of power (but that could just be in my head). Those last two items are what made me think that maybe my injectors were dirty.

My latest research today had me looking at the fuel delivery system, which would go along with your thinking of a lean misfire (I think). And, my Hayne's manual lists "Fuel not reaching fuel injection system" as a possible cause of "Engine hard to start when hot". So that seems like the next logical place to look.

Edit: I just checked my service records, and my fuel filter was changed only 17K km ago. Still pretty new.
Modified by stocker2000 at 11:06 PM 4/19/2005

[NISTECH]

if your fuel economy is down that means you have a rich condition, but that may only be showing up when the car actually runs. really get a look at that airflow meter with a volt meter,that is your primary input for fuel.

If the injectors where dirty it would restrict fuel slightly and not give you the rich condition to bring your economy down. Further more you would tend to see the injector problem more so at idle in the form of a miss fire, not really when starting. If they were that bad the car would likley not start and certainly would not run well at any time following an actual start up.

Another thing you could do as a test is to hook up a fuel gauge inline between the fuel filter and injector rail. Get the car to a condition when you'll have a hard start and see if your loosing fuel pressure before you start the car. When you first turn the key to the on position before actually going to crank poistion the system should build the usual 36psi and hold it after the pump stops. If after the pump stops the pressure drops significantly it would indicate you have leak down of fuel pressure, probably into the cyl from either the injectors or their base seals. This in theory could cause a rich missfire on start up which would make the engine shake violently untill the mixture drops closer to a 14.7:1 ratio.

After reviewing what I just wrote I would suggest starting with the leak down test as it kinda points to all your symptoms.

[stocker2000]

The caue of this leaking would have to be something that is sensitive to the temperature of the engine i.e. cold engine, no leaking; warm engine, leaking. So, ya, I suppose it could be a seal or something where the warm, expanded metal has made the seal ineffective.

I think at this point I'm gonna bring it to a mechanical and let them have a look. I'm not so comfortable working on my fuel system. I will definitely let them know of our conversation to try to point them in this direction.

Thanks for you help NISTECH.

[stocker2000]

Brought my car the dealership today, gave them all the info I had, and let them have at it. In true fashion, the car behaved. They checked for codes, timing, fuel pressure, adjusted idle, and a few other things, but didn't find much there.

But, they did replace a small piece of vacuum tubing, which they said was from the EGR valve. When I looked under the hood, the newest looking piece of tubing was the one connecting the EGR valve to the BPT. So, if this line were broken, then the BPT couldn't regulate vacuum to the EGR valve? Would that effect starting AND fuel economy? Fuel economy I could sort of see.

Complicating matters is that the car didn't exhibit hard starting yesterday (before repiars) OR today (after repairs). The only common element was the temperature outside, which was a good 10 degrees C cooler than atanytime I really noticed the problem. So, not only does the hard starting seem to be engien temp. related, it seems to be ambient temp related too.

Only time will tell if this is resolved. I'm just pissed at myself for not having looked at ALL the hoses more closely

[NISTECH]

that hose would have no effect on its starting ability and not noticable enough of a difference on your fuel economy.

[stocker2000]

So, I shouldn't expect much to change then, I'm gathering. I'll have to wait for the temperature to pick up before deciding what to do next. Thanks.