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AR97Pathfinder

Engine Choking After a Warm Start

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On my 97 Pathfinder I'm having an issue where after the vehicle is restarted after a short period of time (20 minutes) or a couple hours it would crank and start but the engine would choke or "bog" down for a couple of seconds and then the rpms would rise back up and level out to normal. If I were to shut it off after this occurs and start back, it fires up like normal. 

 

Cold starts are perfect and engine fires up without any hesitation after. 

 

I don't have any drivability issues, but recently you can feel a very slight roughness when sitting at a stoplight.

 

I am not sure if the roughness is related to the recent EVAP P1441 code that came on after I started getting gas vapors escaping from the canister vent tube. But the issue after warm starting has been occurring before this EVAP issue. 

 

MAF, plugs, leads, distributor, ECT sensor, air filter, intake air temp sensor, tps sensor have all been replace with original Nissan parts. Fuel filter has been changed within the last two years. 

 

I am leaning in the direction of fuel injectors or the fuel pressure regulator. Going to do a fuel pressure test this week.

 

Any ideas of what it could be?

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Fuel pressure regulator is known to rupture it's diaphragm allowing fuel to be drawn into the intake. Easy way (kinda) to see if this has happened, is to pull the vac hose and see if there is fuel in it. 

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9 hours ago, Mr_Reverse said:

Fuel pressure regulator is known to rupture it's diaphragm allowing fuel to be drawn into the intake. Easy way (kinda) to see if this has happened, is to pull the vac hose and see if there is fuel in it. 

Is there a way to pull the vac hose on this or even change it without removing the intake plenum? 

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I know you can get to it on the VG30 without removing anything else. AFAIK the VG33 is the same. I think I replaced that vac line on mine entirely by feel.

 

A leaky reg or injector sounds reasonable to me. If the reg is fine, the next time it struggles/starts rough, shut it off before it can smooth out and check the plugs. If you've got one leaky injector, I'd expect to see one wet plug. Also check your oil, see if it smells like gas.

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I’ll try and reach it by feel and unplug the vac line to it in order to check for fuel leaking from the regulator into the intake. 
 

If that is bad and I reach by feel maybe I’ll be able to change out without plenum removal? I know it’s held by two screws. 
 

If it’s not bad I’ll have to check plugs like you said on next startup struggle.  
 

I can also check fuel pressure with gauge at the fuel rail correct? Correct me if I’m wrong but you remove the fuel pump fuse and wait for engine to die to relieve pressure. Then tee in the gauge at the fuel rail inlet line. Plug fuse back in. Then turn ignition on and wait several seconds and turn off to see if pressure on gauge drops?  

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Yep, that is the basics for testing. You will still have some fuel spray when you pull the hose, but not as much if you don't do the pressure release you describe. The pump will run for only a few seconds unless you start the engine, so you might want to start the engine, check the pressure with the engine idling. Then rev the engine by hand while watching the pressure. It should increase when you open the throttle then drop back when you go back to idle. 

 

With the 3.3, you can get at the vac line if you work at it a bit. It is in a tight space but I have been able to get to it in the past. 

Edited by Mr_Reverse

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I just had a look at my VG30, and if I had to replace the reg on that pig, I would pull the plenum. I'm not sure I could get my finger on the bottom screw, let alone a screwdriver. The plenum's not too bad to remove, though the EGR tube may fight you.

 

And yes, if you hook up a fuel pressure gauge, you should be able to see if the fuel pressure is dropping off. That said, it sounds like your leak is fairly slow (if it takes twenty minutes for it to flood), so you may not see a fast pressure drop even if it is leaking. EC-25 of the '97 manual has a procedure for all that, but doesn't have a spec for how long it should pressure, at least not that I've found.

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So I performed the fuel pressure test.

 

With engine idling it was around 34 PSI. When engine off but turning on ignition it was around 42 PSI. After turning key to off position it dropped to 39 PSI. After 10 minutes the pressure dropped to 36 PSI. After 15 minutes 33 PSI. After 20 minutes it was around 30 PSI.

 

And when connected with engine on and raising rpms, the pressure does increase.

 

It looks like a gradual drop in pressure, but isn't that normal? I pulled the vac line from the regulator, but from the intake end not the regulator end. Didn't see any signs of gasoline in the hose. 

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Not sure if it could be the IACV causing these issues. I have no code for that though. 
 

From the fuel pressure test with the results in the post before it seems as if it’s holding pressure properly. Are these signs of dirty injectors? 
 

Right now I am between injectors and IACV. 

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Yeah, the fuel pressure will bleed off eventually on its own. The only other check I can think of there (short of pulling plugs) is to remove the intake boot, open the throttle (engine off obviously), and see if you can smell gas after letting it sit for the 20 minutes or so that gives it issues.

 

IACV's not a bad thought. I can't remember if the R50's also got a wax element for the cold high idle (holds the throttle open a little more when it's cold). Something to check. The IACV on mine gets sticky and idles lower than it should, sometimes to the point of stalling at lights. The last time it did that, I shot some carb cleaner down the hose that feeds air to the IACV and that cleared it up, at least for a while.

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2 hours ago, Slartibartfast said:

Yeah, the fuel pressure will bleed off eventually on its own. The only other check I can think of there (short of pulling plugs) is to remove the intake boot, open the throttle (engine off obviously), and see if you can smell gas after letting it sit for the 20 minutes or so that gives it issues.

 

IACV's not a bad thought. I can't remember if the R50's also got a wax element for the cold high idle (holds the throttle open a little more when it's cold). Something to check. The IACV on mine gets sticky and idles lower than it should, sometimes to the point of stalling at lights. The last time it did that, I shot some carb cleaner down the hose that feeds air to the IACV and that cleared it up, at least for a while.

Didn’t think of that, I definitely try that out next time it happens. 
 

Yes it does have a wax element for the cold idle. And as a matter of fact when checking it the roller doesn’t go back to the first mark when vehicle warms up. Maybe something to check out. It’s between the first and second mark. 
 

I will also pull the line on IACV and spray some card cleaner. Did you spray it in and connect back line then start engine right away? Or did you wait a bit before restarting? 
 

Thanks

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Isn’t a high idle really the worst problem those thermo wax elements can cause? I do get the fast idle when cold that kicks down. Doesn’t end up going all the way down due to the wax element not expanding all the way. But it goes down to around 800 or 850 rpms. 
 

Gonna try spraying some carb cleaner into the IACV before replacing that for my issue. 

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My thought on the wax element is that it might not be extending when it's supposed to. The element's supposed to open the throttle when the engine's cold. If it's getting lazy and not opening the throttle until the engine is dead cold, it might not be giving the engine as much air as it expects when it's cold-but-not-dead-cold--so it starts, isn't getting as much air as it expects, then bogs for a moment until the IACV picks up the slack. I dunno, I've only seen VG33 idle controls in the service manual, and I haven't worked with one. I don't know how much accuracy the computer expects from a pot of wax with a piston in it, and I'd expect the IACV to do a better job of picking up the slack if it was working right.

 

When I sprayed mine, I sprayed the carb cleaner down the hose towards the IACV and then started it pretty much immediately (don't remember if I hooked the air hose back to the intake pipe first or not). I was hoping the spray would soften whatever schmoo was in the valve, and engine vacuum would suck the cleaner and the dissolved schmoo through the valve. If you let the spray evaporate, it's just moving the schmoo around inside the valve, if it even makes its way to the valve. I think I repeated this process a few times. The engine did not want to start because it was flooded with carb cleaner, but once it cleared that out, it was back to normal. The right way to do this would be to remove the valve and clean it out on the bench, or just replace it, but just spraying it did seem to clear up the stalling issue I'd been having.

 

 

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11 hours ago, Slartibartfast said:

My thought on the wax element is that it might not be extending when it's supposed to. The element's supposed to open the throttle when the engine's cold. If it's getting lazy and not opening the throttle until the engine is dead cold, it might not be giving the engine as much air as it expects when it's cold-but-not-dead-cold--so it starts, isn't getting as much air as it expects, then bogs for a moment until the IACV picks up the slack. I dunno, I've only seen VG33 idle controls in the service manual, and I haven't worked with one. I don't know how much accuracy the computer expects from a pot of wax with a piston in it, and I'd expect the IACV to do a better job of picking up the slack if it was working right.

 

When I sprayed mine, I sprayed the carb cleaner down the hose towards the IACV and then started it pretty much immediately (don't remember if I hooked the air hose back to the intake pipe first or not). I was hoping the spray would soften whatever schmoo was in the valve, and engine vacuum would suck the cleaner and the dissolved schmoo through the valve. If you let the spray evaporate, it's just moving the schmoo around inside the valve, if it even makes its way to the valve. I think I repeated this process a few times. The engine did not want to start because it was flooded with carb cleaner, but once it cleared that out, it was back to normal. The right way to do this would be to remove the valve and clean it out on the bench, or just replace it, but just spraying it did seem to clear up the stalling issue I'd been having.

 

 

Thanks! I’ll try it out and see if there’s any improvement. 

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I forgot to ask, is using the sea foam spray through the intake a good idea as well as some through the line that feed the IACV? 
 

Is it okay for a vehicle with this age and 180,000 miles? I’ve seen people do it on the pathys and qx4s. If so do you feed through the brake booster line as well or through the throttle body boot. 
 

And should you perform an oil change right after? 

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Seafoam's probably less aggressive than carb cleaner, but it also doesn't evaporate as fast, so you could suck some into the valve and let it soak for a few minutes. Might work.

 

This writeup looks like a good place to start. The guy says to change the oil afterwards, but he's also flushing his crankcase. I doubt much of it ends up in the crankcase if you're just doing the intake, but still, probably not a bad idea to wait and do it when you're about to change the oil anyway.

 

I didn't see a change when I seafoamed my '95, though to be fair I don't know that I did it properly. I used a spray can version with the straw in between the throttle body and the intake pipe and all I got out of it was a lot of smoke and a headache. Speaking of which, before you start, make sure you're upwind of the tailpipe. :doh:

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19 hours ago, Slartibartfast said:

Seafoam's probably less aggressive than carb cleaner, but it also doesn't evaporate as fast, so you could suck some into the valve and let it soak for a few minutes. Might work.

 

This writeup looks like a good place to start. The guy says to change the oil afterwards, but he's also flushing his crankcase. I doubt much of it ends up in the crankcase if you're just doing the intake, but still, probably not a bad idea to wait and do it when you're about to change the oil anyway.

 

I didn't see a change when I seafoamed my '95, though to be fair I don't know that I did it properly. I used a spray can version with the straw in between the throttle body and the intake pipe and all I got out of it was a lot of smoke and a headache. Speaking of which, before you start, make sure you're upwind of the tailpipe. :doh:

Doesn’t sound too bad. Did you get any misfires or roughness long after restarting the engine? 
 

I’m only going to do the intake method then change oil after giving it a drive. 
 

I heard about another one called CRC intake cleaner, many use it for GDI engines but it is also for PFI engines. Same method like sea foam, but you leave it to heat soak for an hour then drive. 

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Nope, no misfires, at least not that I remember. I wouldn't be surprised if a heavy application (or the heat soak stuff) made it hard to start and stumbly until it burned off, but I'd expect it to clear up pretty quick once it's running unless the dislodged schmoo fouls a plug or something. I like the idea of the CRC. The more time it has to work, the more I'd expect it to actually do something. I'd definitely change the oil after that one though.

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So I used the CRC Intake cleaner instead. Ran about 3/4 of the can through the brake booster and left it for an hour (enough time to change out my front wiper linkages).


Did some highway driving (50miles) and then changed the oil. Looks like it cleaned something because the oil was dark and only 1700 miles in.  
 

Not too much smoke really, did get a code initially for random misfire but I cleared it out before restarting. No issues driving afterward. 
 

I’ll have to say it fires right up now on startups, warm or cold, with no issues so far. It’s only been about 4 days but have been driving everyday. And idling at stop lights are very smooth. Not that it was terrible before but it is definitely smoother. 
 

Only time will tell if this solved the problem at startup and how long it works for. I’ll probably give it another dose before next oil change. 
 

Going onto my next project now. Changing out the accelerator cable. Shouldn’t be bad at all. 
 

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Hopefully it stays fixed! I might have to look into that stuff before my next oil change. Good luck with the throttle cable.

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On 11/3/2020 at 4:26 PM, Slartibartfast said:

Hopefully it stays fixed! I might have to look into that stuff before my next oil change. Good luck with the throttle cable.

I guess I spoke too soon. The issue came back today again. Went for a 15 min drive to the store and came back to the vehicle after 25 minutes. Started it and it stumbled for a few seconds. Did not get the fast idle on restarts that you would usually get. 

 

But interestingly right after, heavy gas vapors were coming out from the evap canister vent tube. I had this issue a month ago and changed the vacuum cut valve and the bypass valve by the canister and it didnt happen since. Only until today after the stumbling on startup occurred.

 

Is this issue related? Is it the canister and the valve on it that need replacement? 

 

Could it be the purge valve under the hood? I have no code for that though. 

 

It was also warm here today in NYC about 75 degrees but before was cool for the past two weeks. Not sure if the weather is also making the issue more prevalent. 

 

thanks. Really need the help here

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Damn. Would've been too easy, I guess.

 

I'm not familiar with how the R50's evap system is supposed to work, but looking at the diagram on EC-20 of the '97 manual, it looks like there may be an issue with the charcoal canister itself if it's venting fuel vapor out of what's supposed to be an air inlet. I would expect that inlet vent hose to have a one-way valve in it, though the diagram doesn't show one, and the test procedure has you pinch that line off, which suggests there's no check valve. The diagram on EC-231 does show some kind of valve there, though, so, hell if I know. Hopefully someone on here understands that system better than I do and can fill you in. For all I know, you could have a blocked canister purge control valve or vac line that's leaving the fuel vapor nowhere to go except forcing its way out of the inlet.

 

I have read that the R50 canisters can spew carbon into the vac lines, causing valves to jam up, but that's generally discovered because it's setting codes, not because it's dumping fuel vapor.

 

Without a better idea, I'd run through the troubleshooting in the manual to test the components of the evap system and see if one of them comes up as faulty, or if charcoal dumps out when you remove a vacuum line.

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On 11/8/2020 at 3:50 PM, Slartibartfast said:

Damn. Would've been too easy, I guess.

 

I'm not familiar with how the R50's evap system is supposed to work, but looking at the diagram on EC-20 of the '97 manual, it looks like there may be an issue with the charcoal canister itself if it's venting fuel vapor out of what's supposed to be an air inlet. I would expect that inlet vent hose to have a one-way valve in it, though the diagram doesn't show one, and the test procedure has you pinch that line off, which suggests there's no check valve. The diagram on EC-231 does show some kind of valve there, though, so, hell if I know. Hopefully someone on here understands that system better than I do and can fill you in. For all I know, you could have a blocked canister purge control valve or vac line that's leaving the fuel vapor nowhere to go except forcing its way out of the inlet.

 

I have read that the R50 canisters can spew carbon into the vac lines, causing valves to jam up, but that's generally discovered because it's setting codes, not because it's dumping fuel vapor.

 

Without a better idea, I'd run through the troubleshooting in the manual to test the components of the evap system and see if one of them comes up as faulty, or if charcoal dumps out when you remove a vacuum line.

I pulled some plugs and they're very dark brown and appeared fouled along with the gap by eyeball appears to be larger than it should. 


Any thoughts on that in relation to my issue?
 

I'd like to post a pic of it but im not sure, it says my file size is too large.

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Do they all look about the same?

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10 hours ago, Slartibartfast said:

Do they all look about the same?

I took 1,2,3 out they were just about as dirty if not a little more

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