$20 to anyone who can figure out what's wrong

[goofynick6]

Ok, like I said, whoever can come up with an answer as to what is wrong with my car...$20 big ones.

Here's the scenario:

I got the car running in September, and aside from a problem with it stalling when coming to a stop (figured that out now), it was fine. I could drive it for hours and boost 18 psi and be soooo fast. However, just before I had my accident, it started acting up doing the following.

Car starts perfectly, idles smooth, as it warms up it comes down to a nice 750rpm idle (where I like it)...the a/f ratio is about 13.5:1 or so which is fine by me. I can rev it up and it revs really nice and comes back to a nice idle.

Problem: When I close the hood and go for a drive, it starts getting a little lean...after I hit 15psi and come back to a cruising speed or idle, the car is at 19 or 20:1 a/f running super lean and hesitating, stumbling and not wanting to idle...

What's weird? I bring it back to the garage and pop the hood and it calms back down and is ok.

What's more weird? I found that when I lower the hood (not even touching the hood latch yet), the a/f ratio goes from a nice 13.5:1 to 16:1 and it starts hesitating and running erratically. I open the hood, and it falls back to 13.5:1. There's nothing electrical in the hood, it's CF and I don't even touch it to anything when I lower it.

My only weak theory so far: Somehow the hot air under the hood is messing with the maf and confusing the car.

Here's what I know are fine:tps and it's settingtimingfuel settingsfuel pumpfuel filterfuel pressureo2 sensorwalbro 255no codes on ecuthe car runs great with the hood open at idle

HELP!!!!!!!!!

Thanks guys,Nick
Modified by goofynick6 at 9:20 PM 3/17/2005

[krayton]

have you tried taking your hood off and driving around??

and my shot for the 20 bucks is:

..........

??some wierd out of this world vaccum leak!??

[goofynick6]

Boost-leak tested the system to 25 psi. The only leak I find is the manual boost controller, but that I believe is normal.

And no, I haven't had a chance to drive around w/o the hood. It's seriously driving me crazy because the car ran great before WITH the hood.

Nick

[krayton]

what kind of injectors are you running? and are the elec lines ok on them? no loose connections?

[goofynick6]

RX7 turbo II 550cc injectors, top feed, high impedence, just like stock. Connections are good as far as I know.

The whole hood closing issue makes me feel like it is something other than a loose wire...

[krayton]

try driving without the hood yet?

also another shot in the dark: check your wire loom under the drive side fender.

edit: i know you said the hood clears. but couldnt hurt to do a double check. sort of thinking maybe a line of some sort is just touching and getting pushed out of the way when u close it.

[BoostFab]

is the filter on the maf? is the hood clearing the motor? check for any area that might hit the harness?

[lyon23]

here is an idea.. what about the air of the fans that goes out when you open the hood and stays circulating with it down and makes your temp sensor read hotter? I know in my car if it's normal temp with the car on and the fans, it's hotter than if I turn off the car right there and then and just turn on the switch to see the gauges move.

[Wulfgang]

Yeah, check your BOV setup. If you are still using the stock RB20 BOV it was probably really close to (if not bumping) the hood on your S14 before the wreck. With everything shifted a bit from the wreck, your hood could be bumping the BOV hard, causing it to leak air.

Btw, a boost leak check might not catch this since it is a vacuum leak (i.e. the BOV might seal under boost and then begin to leak under vacuum).

[goofynick6]

HKS bypass valve, not in stock location.

Nothing hits my hood, even when I latch it...this problem happens when I don't even let it latch, I just bring it down NEAR closing, so the hood isn't touching anything but the hinges it is connected to.

Nick

[Eikon]

The hamster's get pissed off when you leave them in the dark.

Oh wait.. you say you have a RB and not an SR... sorry my bad.

So you get a change in A/F ratio when the car is parked and you go from open hood to closed (or near closed) hood?

Is there enough room around the air intake... You must suck a pretty high volume of air into that engine? What if you remove the fender liner or something just to see if it's getting enough air? This seems far fetched..I am pretty sure its not it, but...?

The wife says... get a pontiac hood so that you can get RAM AIR. then she agrees with previous post... drive with your hood off to see if you still have the issue.

Will have to put some more thought into this one... you got a stumper.

[AmoebAssassin]

Carbon fiber is conductive, so don't rule out electrical interference...check the engine bay for wires sticking out that could short out or bridge on the hood. The fact that it ran well for some time leads me to believe that some wires rub repeatedly against the hood and wore their insulation off

[USMCgetsome]

hey nick sorry to say it but it's the maf and air filter. Mine does exactly the same bs when i close the hood. So i have to find a new intake pipe for the turbo inlet with the maf on it to get some better flowing air. By the way i have no air filter at all just an open maf. That is untill i figure out wtf is wrong with mine.

[goofynick6]

Was unaware cf was conductive...I'll triple check all wiring anywhere near the hood tomorrow.

Hmm...I might have to make an airbox of sorts and redo my piping to seal it off from the engine bay...yuck! Just doesn't seem right since it didn't do this before, and my buddy's sr20 with same maf and location doesn't do it.

Nick

[Slo_240sx]

Try adding some other extra ground wires, ex. engine to frame frame to batt. Maybe youre cf hood is electrically interfering with something. I know cf likes to have alot of static electricity.

[AmoebAssassin]

Also on a side note, make sure your MAF wires that you presumably extended are well shielded and have no exposed metal or solder points. I know contact/friction between metal/conductive materials creates dynamic electromagnetic fields. When i play with my r/c car, even trying to screw in a metal screw with a metal screwdriver causes the radio to twitch the servos because the reciever is confused by the field generated by the metal on metal contact. It's entirely possible that your CF hood is vibrating against your unibody or hood pins, creating a weak EM field that results in a fluctuating current through your unshielded MAF wires. However, i must admit that this is wild speculation and i could be overthinking the situation...however, you're looking for remedies and this is just a very simple thing to check...so inspect the shielding on your MAF wires.

[Nameless EJ6]

Check coolant temp sensor with hood open and closed.

[goofynick6]

There are about 2-3" of exposed maf wire and my own crimped on terminals and there is some bare metal exposed (don't have a working 300zx plug).

I added 5 large ground wires in the fall and grounded anything important in the engine.

Keep the ideas coming!

Nick

[Wulfgang]

Heh, you guys are pretty funny. The very fact that carbon fiber is conductive means that it will act as a shield to surpress EMI. And I know R/C stuff is glitchy around small sources of EMI, but Nissan and other OEMs don't play around. After all, the ignition system alone puts out more RF than your local radio station! Just kidding, but really, your ECU, MAF, etc. were designed to be used in a very, very noisy and harsh environment.

There is a maxim or proverb... forgot who said it, but it goes something like this: The simplest explanation is usually the correct one. So yeah, check the MAF wiring/shielding, anything bumping the hood, etc.

It is highly unlikely that your MAF, which measures true mass flow regardless of temperature, is affected by the under hood temperature (unless it is through a wiring short). And it is equally unlikely that your cf hood is causing electrical interference.

I also doubt it would have to do with the coolant sensor, since that is used to richen the mixture over the base maps and your problem is leaning out.

[goofynick6]

I'll recheck everything (heading out now to the garage), but I'm pretty sure there are no wires touching the hood.

The coolant sensor didn't affect things, even with it unplugged it did the same thing.

Maybe my MAF just doesn't like hot air? I'm gonna go rewire the maf and try another from a friend..wish me luck.

Nick

[krayton]

try driving without the hood yet?

[Nameless EJ6]

The coolant sensor didn't affect things, even with it unplugged it did the same thing.Nick

It should. Check the voltage. If it's not doing jack ****, then that's the problem.

[rbpwr240]

how about unpluging the maf abd seeing if it runs like when you close the hood, also just take the hood off couldn't hurt to try.

[goofynick6]

I have an fp gauge on the rail and it is at 36 idle, 43 w/o vacuum.

I tried a totally different MAF today from a friend (also 300zx maf) and it did exactly the same.

I totally rewired the MAF wiring with all new shielded wire and a proper maf plug. Redid the o2 sensor wiring with all new shielded wiring; nothing helped.

The hood is absolutely not touching any wires, and another guy said that if anything, the CF hood should help block out electric frequencies and help to shield the engine bay more than anything.

Didn't get a chance to drive w/o the hood before it got too late, so don't know about that.

So...any other ideas?

Nick

[goofynick6]

It should. Check the voltage. If it's not doing jack ****, then that's the problem.

Well, when I just unplugged it, the a/f would get about 2 points richer, so it IS working, I just meant it didn't make a difference on the hood issue.

When I unplug the maf, the car barely runs, so I didn't get to try the hood thing w/o it plugged in.

Any other ideas?

[goofynick6]

There is a maxim or proverb... forgot who said it, but it goes something like this: The simplest explanation is usually the correct one.

Ockham's Razor: All things being equal, the simplest explanation is usually correct. I'm wishing it was something simple, because I'm running out of things to check; I'm about ready to put megasquirt on it for the fuel system!

Nick
Modified by goofynick6 at 9:21 PM 3/18/2005

[hiprollc]

Not after your $20 but I would seriously check the shield on the extended MAF wiring. I have seen similar "inconsistencies" when wiring a harness where I didn't get the shield properly rewrapped. So, even if the hood isn't touching the harness at all, if there is a problem with the shielding, even the CF hood may induce a false signal or simply affect the actual output. If the hood is touching, repositioning the wires could certainly also affect the signal with poor shielding.

[goofynick6]

As I said, I redid all of the maf wiring today that was extended. I wrapped extra shielding around the areas that were being spliced and made sure the shielding was grounded. I also redid all of the wiring right up to the plug itself and added lots of shielding there as well. The car used to run great on a less "quality" wiring job, so that's not it.

Nick

[BoostFab]

could the maf be damage during the accident? have you tested with another one?

[goofynick6]

I just posted that a few posts up that I tried a new MAF today...same thing.

Nick