Fuel smell in cabin windows down

[mk2davis]

Hello all, I'm trying to track down the cause of a unavoidable fuel smell I get driving down the freeway with the passenger window partially open. No recent work on the car to speak of, windows up = no smell. With the car parked and off I smell a little of it, mostly in the area of the fuel filler and evac canister. Mileage leaves a bit to be desired... IIRC about 21 +/- 1 and I don't run her hard.

Based on a search, I've found the following possible sources:

- fuel filler neck - cheap, but sounds like a pain in the @ss. If you have a write up or a how to, that would be appreciated
- EVAC canister - looks easy, but canisters are 250 and up
- tank to fuel pump line - seems not uncommon
- injector o rings - seems common, but I didn't smell anything directly over engine
- other? - there's always "other"

What I'm looking for is a way to narrow the search down a bit. I dont mind getting my hands dirty, but I despise wasting time or money.

Is there a way to troubleshoot this a bit and narrow the options (hopefully to 1 thing)? Is there something I am missing?

TIA

 

[Old Guy]

Before spending money on things, I would arrange for a low pressure test of the evap system or a smoke test to look for evap system leaks.

The other test that you can do is a pressure test on the fuel system. With a pressure tester connected to the fuel system, run the pump to charge the fuel rail up to rated pressure, shut the pump off and then watch how quickly you lose pressure. If its fairly quick, you might have a leak in the fuel system somewhere or a drooling injector. Of course, it could also be a leaky fuel pressure regulator draining through the return line or a leaking check valve on the pump, neither of which are critical issues.

Is your car OBD II? Getting a code reader and checking for pending or stored codes may indicate problems with the Evap system or fuel mixture problems.

 

[mk2davis]

I am OBD 1. Thanks Old Guy, this was exactly what I was looking for. I'll start with the EVAC check and then the FP check. Silly question, how quick is "fairly quick"?

If both of these test good, would you then suspect the filler hose?

This will be a slow process. She isn't my daily. I'm kinda hoping it's the injectors, I gotta pull them out and send them to RC Engineering at some point anyways.

 

[SWFL_NSX]

You might also try to locate the leak by smell when the car is running and stationary. Some of the stuff you're questioning may only leak under pressure (fuel injectors) or when the car is running (Evap).

If the injectors are a maintenance item for you it might be time to change the fuel filter that is in the engine compartment. You'll have the system depressurized so it makes sense to do at the same time.

Depending on mileage and age it may also be time to change your fuel pump. This is a harder DIY but not impossible, and should be considered if you decide to drop the tank (I assume this is necessary to inspect/replace the filler neck, it may not be).

Two threads from Prime regarding fuel smell in cabin:

http://www.nsxprime.com/forum/showthread.php/163482-Gasoline-exhaust-smell-in-cabin

http://www.nsxprime.com/forum/showthread.php/127334-2005-NSX-Leaking-Gas

 

[Old Guy]

I am OBD 1. Thanks Old Guy, this was exactly what I was looking for. I'll start with the EVAC check and then the FP check. Silly question, how quick is "fairly quick"?

If both of these test good, would you then suspect the filler hose?

This will be a slow process. She isn't my daily. I'm kinda hoping it's the injectors, I gotta pull them out and send them to RC Engineering at some point anyways.

An acceptable rate of pressure drop in the fuel system is a one of those experience things - like sussing out the readings on a cylinder leak down test. I have never done a fuel supply pressure test on the NSX; but, on my other vintage car with EFI the fuel pressure declines fairly slowly on shut down. Probably about 1-2 psi per minute initially; but, slowing down in the rate as the pressure drops. If the initial rate is 1 psi a minute or less, you probably do not have a fuel supply leak. If the drop rate is really fast then it could be the pump check valve or the fuel pressure regulator leaking which is not a big deal. If you are smelling gas on a vehicle walk around it may not be the actual injector valve leaking; but, it could be the connection between the injector and the fuel rail that is leaking. With the fuel supply system pressurized it is moderately easy (compared to other things!) to inspect the fuel rail to check for leaks.

If you do an evap system pressure test / smoke test that 'likely' catches any leaks in the fuel filler / gas cap system. The reason I say likely is that your car is pre OBDII. Most OBDII vehicles have a green service / test port on their evap system (although I don't ever recall seeing one on my 2000 NSX). Without getting my hands on the manual for a smoke test machine I don't know the details of how you execute a smoke test on a pre OBDII car. You are going to have to outsource the smoke test since you don't want to be forking over the $ for the machine so leave that detail to the shop doing the test who hopefully know what they are doing. As an observation, I expect that replacing the fuel filler hose requires dropping the fuel tank. That is not a technically complicated process; but, it is a lot of work so you want to make sure that the filler is the problem before you do that. If you do drop the tank, if the pump on your car is original you might want to consider replacing it as preventative maintenance. If the pump failed in a year or two from now it would really chap my butt to have to drop the tank again to replace the pump.

Start with the fuel supply system pressure test and check for fuel leaks just because that is something that you can do for the relatively small expense of a fuel pressure tester and an adapter to fit the NSX fuel system. I am trying to remember the details of the location for the adapter (I don't have my SM handy). I think the fitting goes on the fuel filter so you might want to have some fresh crush washers on hand when you remove the adapter. The other thing you can do is to purchase some UV dye for the fuel system along with a test lamp and glasses. Dump the dye in the gas tank and drive around for a couple hundred km and then inspect the fuel system with the lamp to look for the dye traces. This can be helpful for those really slow leaks. If nothing shows up on the fuel supply system then find a competent shop that can do a smoke test of the evap system.

 

[mk2davis]

Thank you gents for the input. It's a 91 with 116k miles. You are right, if injectors are coming out then the fuel filter will get replaced. If the tank is coming out, then a new pump will be going in.

I'll get a loaner FP tester and see what it says. I appreciate everyone's input.

 

[mk2davis]

Idled the car while stationary, and with my sniffer in between the EVAC and fuel filler hose, I smell slight whiffs.

I did the FP test, and she passed with flying colors. Once turned off, pressure dropped about 1 pound over the course of a minute. Per the gauge, every thing on that end seemed to be good. Will still need to send the injectors in at some point, but those are not the cause of the issue at hand.

Previous owner put on those faux SS braided "I really want to be AN fittings" vacuum lines that I am not a fan of, so I replaced those. Started the car, shoved my nose next to the EVAC can, and (for now anyways) no gas smell! Maybe the rubber smell is just overpowering the gas. Or maybe I got lucky and it's just a cracked line. I'm going to drive her tomorrow before the rain comes, but here's to steps in the right direction.

Thank you all!