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Discussion Starter #1
This problem has got me confused as I can't really think of anything that would cause it, but hopefully, one of your guys might have an idea.

A couple of months back, I had to remove the battery from my car which obviously had the effect of reseting the ECU. No problem I thought, since it will re-learn the engine in a weeks worth of driving or so. Prior to this, the car drove great, although the fuel consumption was a little high (but nothing major).

After resetting it, I noticed that performance seemed to be reduced, even after allowing the ECU to "learn" the engine. I tried resetting the ECU again, but the same result.

The thing is, over the past 1500 miles or so, the problem has got even worse. There are no obvious signs that anything is wrong with the engine, and this is the bit that *REALLY* confuses me - my fuel economy has gone *UP* by 3 or 4 mpgs - thats like 10%!

The car is due for a service so I'm hoping that might cure the fault, but I won't hold my breath.

The things I've checked are as follows:

  • No smoke from exhaust
  • Oil level is fine, and doesn't consume any oil.
  • Oil and filter were last changed 4500 miles ago.
  • Coolant level is fine, and temp gauge sits exactly on halfway.
  • Using same grade of fuel - 95 octane (thats the Euro octane scale though)
  • No "rotten egg" smells, so I think the cat is functioning correctly.
  • No engine check light
  • No hissing noises, so I doubt there is a vacuum leak
  • Spark plugs were changed about 4500 miles ago, and don't show any obvious signs of engine trouble
  • Distributer hasn't moved to affect timing
  • Spark plug leads clean and have been re-seated
  • K&N airfilter looks clean and is only a few months old
  • Idles smoothly at about 750rpm
  • Seems to pull smoothly throughout the entire rev range without pinking or stuttering
  • Always starts first time from both cold and hot
  • Battery is less than a year old, and the alternator appears to function OK
  • Car has 45500 miles on it and is 3 1/2 years old
  • This is a Euro spec SR20, so no EGR or any of that emissions crap
Any ideas people? The only things I could think of is that either the MAF is telling the engine it isn't getting enough air (and is therefore not injecting as much fuel), or that the engine is recieving low fuel pressure, maybe a knackered pump or blocked filter causing it to run lean. If it was running lean, then the ECU would retard the timing to prevent knocking, and give crappy performance.

Other than the K&N airfilter, the engine is stock.

The car behaves perfectly, except that it is as slow as a granny on her zimmerframe. Damn, before long I'll be spanked by Geo Metro drivers


Thanks in advance - Anthony.

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1997 UK spec P11 Primera
http://www.primeraweb.co.uk
 
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Discussion Starter #2
sounds like your ECU is f**ked.. sorry im no help but i think that ECU needs its mental refreshed.
 
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Discussion Starter #3
What's a "zimmerframe"??

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Wheel gap is the enemy. "Silver" 2001 SE w/perf.pkg, PR CAI, Intrax.
 
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Not entirely sure what you call them on your side of the pond, but a "zimmerframe" is the metal support thing that you see frail old ladies supporting themselves on.

Either way, it doesn't affect the main point of this post - has anyone got any ideas what the hell is up with my car?

Oh, and I forgot to add to the list of things I'd checked:
  • All (visable) engine wiring connectors re-seated
  • Tires at correct pressure
  • Brakes aren't binding, and the wheel bearings seem to turn freely enough
I don't think that the ECU is knackered, as the car still runs fine. I guess I could get hold of another to swap it out with to prove it though. The best way I can describe the fault is that it feels like someone has swapped my nice SR20 for a GA16 or something.

And before you ask, yes I have checked that I still have a SR20DE under the bonnet!


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1997 UK spec P11 Primera
http://www.primeraweb.co.uk
 

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<font face="Verdana, Arial" size="2">Originally posted by Ang!:
...but a "zimmerframe" is the metal support thing that you see frail old ladies supporting themselves on.</font>
Oh! a walker.
 
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Oh cooooooooooooooooooooooooooooolllllllllllll. Ang!'s gotta Primera! I wanted to lay my hand on one of those. emmm~~~~~.


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'95 Infinity G20 f/l, 5 spd, all stock.
Team Dynamics Nissan Primera '00 at Brands Hatch
 
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I've got to admit, I hadn't checked the grounding of the MAF sensor. If it is a bad ground, then that would explain the problem I'm getting I guess, as the engine would be getting a different amount of air to what it thinks it should be getting.

Thanks for the suggestion - I'll check that out later on today, if it stops raining


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1997 UK spec P11 Primera
http://www.primeraweb.co.uk
 
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Discussion Starter #9
I checked out the MAF and the voltage difference is slightly above spec at 0.011v as opposed to the 0.009v or below it is supposed to be. I'll re-ground it later, but I don't think that is likely to be the problem.

I also checked out the TPS sensor voltages, and they are correct at 0.48v with the trottle closed, and 4.15v with the trottle fully open.

I'll let you know if the re-ground sorts it, but any other suggestions of things to check?

Thanks again all for your help - Anthony.

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1997 UK spec P11 Primera
http://www.primeraweb.co.uk
 

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fuel filter, checktiming once again.sp wires.

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91 SE-R,10:1 comp.pistons,balanced &blueprint rebuild.comp.4angle valve job,extrude honed heads/intake manifold,No emissions.crap,RC TB/MAF,nismo cams,UR pulleys,stillen4-1 ceram.header,nismo/centerforce dual fric.clutch,PR CAI with POPchgr,2 1/2 test pipe,mandrel 2 1/4 superturbo ex., ZEX flywheel & JW 50 shot nos with 60 shot jet. and much more goodies!
 

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hey AUG i read the same article on the TPS at 0.48 but is that ac or dc volts. because when i check it onlt went up to 0.22v may my meter is bad
 
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Discussion Starter #12
Thats in DC volts.

Measure across pins 1 and 2 with the throttle in the "idle" position, and it should read around 0.5v.

Then twist the throttle cam and the voltage should smoothly rise as you open the throttle further, until reaching a maximum of around 4v at full throttle.

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1997 UK spec P11 Primera
http://www.primeraweb.co.uk
 
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The best way I can describe the power loss is that it feels more like there is a GA16 under the bonnet rather than my SR20.

The main bit where I notice the missing power is that the power "hump" between 3500rpm and about 5500rpm has vanished. You used to be able to feel the engine pick up through this rev range, but now it doesn't. It feels like the engine does below 3000rpm the entire way through the rev range.

I tested the car on a piece of road I can measure the cars performance on. From a standing start going up a slight hill, I used to be able to get to 103mph by the time I passed under the bridge near the top. Now I'm struggling to get 90mph doing the same thing.

Interestingly enough, I tested it when the engine was cold, and therefore would be running in "open loop" and running extra rich etc to warm up the cat. The car felt noticably quicker in the powerband than when it is warmed up and in "closed loop".

I can therefore draw the conclusion that the problem isn't mechanical as such, but must instead be either a sensor issue (most of them are ignored during warm-up I believe) or the ECU is running the car too lean, and hence it runs OK when the mixture is richened to warm the cat up.

However, the spark plugs don't show any signs of lean running. The sensors I checked appeared to be functioning correctly (well, the MAF ground was *slightly* out of spec, but only by 0.002v).

Trust me never to get the "simple to diagnose and fix" faults...


I have never changed the distributor cap or rotor, but surely if these were screwy, wouldn't they screw up it when the engine was cold too? I guess I could take it apart and see if there is any obvious signs of wear in there, and whilst there I might as well do the Wayne Cox HP trick thing I remember reading about on SE-R.net


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1997 UK spec P11 Primera
http://www.primeraweb.co.uk
 

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Originally posted by
The best way I can describe the power loss is that it feels more like there is a GA16 under the bonnet rather than my SR20.

The main bit where I notice the missing power is that the power "hump" between 3500rpm and about 5500rpm has vanished. You used to be able to feel the engine pick up through this rev range, but now it doesn't. It feels like the engine does below 3000rpm the entire way through the rev range.

I tested the car on a piece of road I can measure the cars performance on. From a standing start going up a slight hill, I used to be able to get to 103mph by the time I passed under the bridge near the top. Now I'm struggling to get 90mph doing the same thing.

Interestingly enough, I tested it when the engine was cold, and therefore would be running in "open loop" and running extra rich etc to warm up the cat. The car felt noticably quicker in the powerband than when it is warmed up and in "closed loop".

I can therefore draw the conclusion that the problem isn't mechanical as such, but must instead be either a sensor issue (most of them are ignored during warm-up I believe) or the ECU is running the car too lean, and hence it runs OK when the mixture is richened to warm the cat up.

However, the spark plugs don't show any signs of lean running. The sensors I checked appeared to be functioning correctly (well, the MAF ground was *slightly* out of spec, but only by 0.002v).

Trust me never to get the "simple to diagnose and fix" faults...


I have never changed the distributor cap or rotor, but surely if these were screwy, wouldn't they screw up it when the engine was cold too? I guess I could take it apart and see if there is any obvious signs of wear in there, and whilst there I might as well do the Wayne Cox HP trick thing I remember reading about on SE-R.net


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1997 UK spec P11 Primera
http://www.primeraweb.co.uk

Hi there

I know how you feel!! I have the same problem with my 1998 Nissan Sabre (South Africa pulsar sss http://members.pulsar.org.au/profiledisplay.php?ID=1303)

I have been advised the it is the Fuel pump packing up. Get you fuel pressure checked??? Mine is at about 2 bar where it should be at about 2.5 to 3bar.

?????
 
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