# Need help with misfire can figure it out



## fufhubbin (Jun 8, 2015)

Car is misfiring. Idle is low and bounces from 100 to 350rpm constantly. Can maintain idle for 10+ min no problem but when accelerated wont Rev past 800 or 1000 rpm . Car smells kind of like sunburned gasoline smell after you try to Rev it. Doesn't Rev to 800 or 1000 rpm consistently. Seems very choked if you mash on gas. But if slowly applied gets up near 1000

Already changed cap and rotor plugs and wires and check fuel filter. Going to clean and check mass air flow sensor tomorrow first thing any advice please would help thanks!


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## fufhubbin (Jun 8, 2015)

Bump please any advice


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## jdg (Aug 27, 2009)

Check the fuel pressure regulator vacuum line, and/or put a fuel pressure gauge on the rail and see what's what...


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## fufhubbin (Jun 8, 2015)

There's no spot on the rail for it how else can I check fuel pressure


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## fufhubbin (Jun 8, 2015)

Also the car keeps getting better and worse. Like when I'm there giving it gas where it tops out at 1000rpm. With the same steady amount of throttle it will drop in rpms and get all bouncy on the rpms ....still keeping same amount of throttle it will recover after a few seconds and get back up to 1000


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## jdg (Aug 27, 2009)

Which engine? Which car?


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## rogoman (Dec 16, 2004)

fufhubbin said:


> There's no spot on the rail for it how else can I check fuel pressure


In your case, tee-in a temporary fuel pressure gauge at the output side of the fuel filter. The readings at idle should be as follows:
- with vacuum hose connected to the fuel pressure regulator: 34 psi
- with vacuum hose disconnected from the fuel pressure regulator: 43 psi


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## fufhubbin (Jun 8, 2015)

So I just checked the fuel pressure and its 43. Not sire what you were saying to get 34 but it reads 43. My friends dad that works on cars and builds racecars thinks that since that's good I should just drain the fuel put in new fuel and put in a new fuel filter and it should run. I don't feel like that's the case what would be ur opinion so far. I will be stopping by to get an oxygen sensor tonight and rechecking the codes to see if it changes


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## fufhubbin (Jun 8, 2015)

Someone also suggested that the Cadillac converter is clogged but I had a new one installed 8 months ago as well as new exhaust. But someone told me there's 2 on some cars I'd it possible that my other one is clogged

Also does it rule out that its nit a vacuum leak if I blew smoke from my ecig in the engine through a vacuume line and its nit comming out anywhere. I'm blowing a lot of smoke in there as hard as I can to make sure and a little is leaking back out through the air intake Way in the front of the engine so can vacuum leak be ruled out ?


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## jdg (Aug 27, 2009)

You obviously didn't check the fuel pressure the way rogoman asked you to check it.
If you did, you would've came up with 2 numbers...one with the vacuum line connected to the regulator, and one without the vacuum line connected to the regulator.
IF the 43 value you got was with the vacuum line both connected and disconnected, either your regulator is bad or the vacuum line going to the regulator is bad.
That 43 value is ONLY good if the vacuum line is disconnected.

Tell your "friends dad that works on race cars" the vacuum line modulates the fuel pressure regulator output pressure with respect to the intake manifold pressure to maintain a constant fuel pressure differential across the fuel injector tip and intake manifold.
If that blows his mind, go elsewhere...

Think I'm making it up?
Think again...


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## fufhubbin (Jun 8, 2015)

That post is amazing. I will be sure to read that to him he thinks the fourms people don't k ow what they are talking about....clearly you and rogoman know this stuff inside out


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## fufhubbin (Jun 8, 2015)

I'm gonna check this as soon as I wake up. So if the hose to the fuel pressure regulator has no holes and is sealed the. Its likley that the regulator is bad? Someone on here was talking about using a tee in vacuum gauge on that vacuum hose. If I can get that set up. What numbers should it read


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## jdg (Aug 27, 2009)

Same as any other well running engine, ~18" manifold vacuum at idle (but depends on engine condition, altitude, temperature, etc., could be as low as around 15, could be up around 20, as long as it's steady and not 0), and drops towards 0" when you punch the gas.


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## fufhubbin (Jun 8, 2015)

Didn't check the vacuum pressure o That yet. But when I disconnected. The vacuum line from the fpr there was no fuel that dripped out.. and the fuel pressure rose from 43 when it was plugged it to 50 when it was unplugged. As soon as I shut off the car it dropped to 43. And when I'm checking g it with it plugged in.....when I shut off the car it drops like 2 psi right away them slowing goes Dow. Maybe 10psi in 10min. What's my next step lol


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## jdg (Aug 27, 2009)

Why "lol"? Is it funny or something?
You know what else might help decode your problem? Correct spelling, correct punctuation, etc.

If those numbers are what you actually got, they're both about ~7 PSI high, suggesting a blocked fuel return line, bad fuel pressure regulator, or possibly the fuel pressure gauge itself is reading ~7 PSI high.
And the fuel pressure dropping after you shut the vehicle off might suggest a bad check valve in the fuel pump.

Again...not brain surgery for the experienced. What say your friend's dad that builds race cars now?


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## fufhubbin (Jun 8, 2015)

The guy that builds racecars keeps thinking contaminated fuel. when it was at his house he looked at it and had a friend of his that owns a mechanic shop . They didn't want to put to much time into it since they have a huge list of projects. They put in 3 gallons of their fuel that is "not contaminated" and added an extra ground to the mass airflow sensor. No difference. They are also the ones that installed my new cap and rotor,spark plug and spark plug wires.....I had those changed cause when it broke Down I had to towed to a shop and they diagnosed it with that but I was trying to be cheap so I had them do it

I put a bottle of fuel system cleaner in it a week ago and a bottle of heet. I pumped some fuel into a bottle and let it set overnight to see of anything unusual settles at the bottom


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## jdg (Aug 27, 2009)

fufhubbin said:


> The guy that builds racecars keeps thinking contaminated fuel. when it was at his house he looked at it and had a friend of his that owns a mechanic shop . They didn't want to put to much time into it since they have a huge list of projects. They put in 3 gallons of their fuel that is "not contaminated" and added an extra ground to the mass airflow sensor. No difference. They are also the ones that installed my new cap and rotor,spark plug and spark plug wires.....I had those changed cause when it broke Down I had to towed to a shop and they diagnosed it with that but I was trying to be cheap so I had them do it
> 
> I put a bottle of fuel system cleaner in it a week ago and a bottle of heet. I pumped some fuel into a bottle and let it set overnight to see of anything unusual settles at the bottom


Thank you.

Vacuum test is one of the things up next. And maybe try to verify that fuel pressure gauge is at least halfway accurate. Doesn't need to be dead nuts on, but that 7 PSI is suspect.


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## fufhubbin (Jun 8, 2015)

SOLVED!

sprayed the special mass airflow cleaner in the mass airflow sensor. And tried to start it and still same issue....... packed everything up then decided to check for a last thing.vacuum pressure. My dad was watching the gauge and I was getting 10 to 14 psi when I was between 500 and 1000 rpm and I was trying to have him get a reading when I was at the highest rpm I could go and it was letting me get 1500rpm all the sudden... so I kept steady throttle for about 10seconds and it just started working! So excited!

The fuel pressure is a heavy duty rental from autozone and I wanted to check the pressure after the fix to see if it had anything to do with the high fuel pressure. It did not still 43 and 50 with the vacumm unplugged.


Thanks everyone on here for the assistance!

Only things that's super duper annoying is my dad brought the spray to the roadside the day I broke Down and he forgot to try it cause I kept thinking vacuum leak. And. Cause of that I got my speakers stolen! Grrrr


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## jdg (Aug 27, 2009)

Sounds like you gas fouled the plugs and that little run with a bit of spray from the MAF sensor cleaned them off.

I'm assuming you actually have a '95-'99 B14 Sentra or 200SX with a GA16DE engine, which this only applies to these models...(might apply to the earlier B14's, 91-94, not sure though)...

These engines don't like short runs...like the kind where you take the car out of the garage and park it next to the garage, or out of the garage and park it on the street. A quicky start/stop to move the car somewhere else, maybe less than a minute or so.
Doing so tends to gas foul the plugs and cause a rough start (if any start at all) next time around. It's happened to me a few times accidentally, and I've been able to duplicate the issue the two times I've attempted it (at the expense of a new set of plugs), and there's a handful of threads here about it happening to other folks as well.
Don't know exactly why it happens, don't really care, it just does happen. Call it a quirk. It may run well now, but it'll screw up again. That's all there is to it. Case closed. Sure, you can clean the plugs. Or at least you think you can clean the plugs. I've tried. Doesn't work.
Change the plugs again. Use the recommended NGK plugs. No Bosch, No AC/Delco, no nothing. Just NGK plugs of the proper heat range. That's it.


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## fufhubbin (Jun 8, 2015)

I will. Buy these special plus you said Even thou I changed thwm while it was acting up and it didn't help. I did buy boshe thou ha


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## fufhubbin (Jun 8, 2015)

94 altima 75k mikes


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## jdg (Aug 27, 2009)

So...it's an Altima?

By chance, have you looked at the top of the page to see what's what?

So...disregard post #19 as it has zero bearing on this conversation. Why? Because the O/P doesn't know where to post his/her issues.


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## rogoman (Dec 16, 2004)

fufhubbin said:


> SOLVED!
> 
> sprayed the special mass airflow cleaner in the mass airflow sensor. And tried to start it and still same issue....... packed everything up then decided to check for a last thing.vacuum pressure. My dad was watching the gauge and I was getting 10 to 14 psi when I was between 500 and 1000 rpm and I was trying to have him get a reading when I was at the highest rpm I could go and it was letting me get 1500rpm all the sudden... so I kept steady throttle for about 10seconds and it just started working! So excited!
> 
> The fuel pressure is a heavy duty rental from autozone and I wanted to check the pressure after the fix to see if it had anything to do with the high fuel pressure. It did not still 43 and 50 with the vacumm unplugged.


The first thing you should be doing is perform an ECU code readout to see if any fault codes are set; if any codes are set, they can help you to diagnose your problem.

If you're only getting 10 - 14 InHg on your vacuum gauge, then either you're not connected to a full vacuum source or there is a major vacuum leak in the intake system.

By the way, there's no such thing as 'vacuum pressure'. Vacuum is absence of pressure.

To properly check the intake system for a vacuum leak, attach the vacuum gauge to a FULL vacuum source. A good place to connect to is the charcoal canister. There should be three hoses connecting the carbon canister. Two of the hoses go to a purge valve that's built into the canister. The second larger hose off the purge valve should be your vacuum line. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg.

If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.

A fuel pressure of 50 psi is way too high for your engine; it'll possibly cause injector leaking. If there's no change to the pressure with the vacuum hose on or off the FPR, then either there's no vacuum at the hose or the FPR is bad.


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## jdg (Aug 27, 2009)

Did you catch that he/she actually has an Altima rather than a B14?
...not that it matters much. The troubleshooting mentioned above obviously applies to all vehicles...but...nonetheless.


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## rogoman (Dec 16, 2004)

Yes JDG, I did see that it was an Altima after so many posts. That's the whole problem here on the forum where so many members don't describe their vehicle. A common one: can't start my car. That's it! I guess we're supposed to to be mind readers or have X-ray vision; LOL!!!


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## jdg (Aug 27, 2009)

Person A - My car won't start.
Person B - What kind of car do you have?
Person A - I think it's a blue one.
Person B gives Person A a round house kick to the groin.


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## Shut-Trip (Oct 18, 2012)

I work in a Computer Help desk, and we always ask customers some questions about their computers, 
the same may apply for cars/ mechnaics, I presume:

Some Simple Comments / Observation:

Please provide the following information for proper response:


++++++++++++++++++++++++++++++++++++

Name:
Car Make: 
Car Model: 
Car Year:
Engine Model:
Trans Model:
Mileage:

Problem:


sample:




++++++++++++++++++++++++++++++++++++

Name:shunt-trip
Car Make: 97Nissan
Car Model: P/U
Car Year:'97
Engine Model:24 Liter 4Cy.
Trans Model:Auto
Mileage:202KMiles

Problem:

Water spots on Speedometer, and Techometer / dash
















Car is misfiring. Idle is low and bounces from 100 to 350rpm constantly.


++++++++++++++++++++++++++++++++++++


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