Rb25det Miss Fire

[l0WRB]

got a really weird problem with my r33 rb25det

mods are

cooler

exhaust

walbro pump

now im using a blitz ebc and ive got stock boost setting 7psi and high which is 10psi

the plugs are gapped at .8mm copper ngk plugs and ive tapped up the coils

but the car will only miss fire either at nite(cold air) or early mornings(cold air) on way 2 work 8am.

i drove it around for about an hour today around 1-2pm and it would rev fine on 10psi all the way to 7000rpm, driving home from mates place before 8pm colder air, it would just miss fire from 4500rpm onwards wether on high/low boost

would any of you guys have any idea wot this could be? maybe AFM?

thanx

Justin

Edited July 21, 2006 by l0WRB

[sinistaGTR]

it might be getting higher boost (creep) due to the cold weather and the boost cut from the stock ecu is kicking in....

[l0WRB]

it might be getting higher boost (creep) due to the cold weather and the boost cut from the stock ecu is kicking in....

hey mate, nah ive felt boost cut before and it nearly thru me thru the windscreen LOL

the boost barely spikes above 10psi ive got it set to it creeps up and just gets to 10psi

so im buggered as to wot it could be ?

[subzeroR33]

Could be your map sensor.

[l0WRB]

Could be your map sensor.

how do i check my map sensor? where abouts is it located

[FATGTS-R]

There is no Map sensor.

Does it still happen if your on the low bost setting?

Sounds like the common rich and retard(search).

[subzeroR33]

There is no Map sensor.

Does it still happen if your on the low bost setting?

Sounds like the common rich and retard(search).

Well i dont know about your car but mine has a map sensor, it used to break down as it would only read up to 19psi and my car would sometimes hit 22psi when it was cold, it would miss and break down over 5000 revs. My mechanic reduced the boost and it hasnt missed since then.

[T04GTR]

how longs a piece of string?

[subzeroR33]

If you have the money long as you want

[T04GTR]

spark blowing out.

either caused by weak spark or to lean mixture.

so.. afm,fuel pump,igniter,coils,boost leak...

check the fuel presure first:d (while driving obviously)

[l0WRB]

There is no Map sensor.

Does it still happen if your on the low bost setting?

Sounds like the common rich and retard(search).

i can turn the ebc down as low as it can go 7psi stock and it still splutters and farts up thru top end. wont rev out cleanly

[rob82]

spark blowing out.

either caused by weak spark or to lean mixture.

so.. afm,fuel pump,igniter,coils,boost leak...

check the fuel presure first:d (while driving obviously)

There is a heap of other reasons as well. Check you base timing.

[benl1981]

I found on a cold night I would get hesitation etc whenI fitted the R34 intercooler...

Even on stock boost - It could be the ECU playing with the fuel and ignition timing. If you have a mate that cn lend you a powerfc wack it in and try it on the base map..

[skylineking]

just a question when was the last time the car was professionaly dyno tuned, cause they can fix most mixture problems with those mods on a stock ecu and tell u if any sensors and dead or not functioning properly.

[Taso84]

I got a similar problem with mine.

33 GTST

POD

Cooler

CATBACK

Apparently its either the coilpack or sparkies, thats wat i heard. I'd check these out first.

Difference is mine does it in all weather and at 5.5 - 6 RPM

Correct me if im wrong guys

[BHDave]

For justin- you are probably on the edge of the r & r mapping and the cold denser air is tipping you over the edge. Combined with old coils you begin to get the miss as the mixtrues are richer. Check the heat range plugs you are running too. You want a 6.

I'd put it on a dyno before doing anything though and see what your arf's are doing. It will eliminate afm's/fuel pumps/fuel filters/injectors from the list of possibles for 60 bucks. Then start looking at spark.

Taso- your's is almost certainly coils, but try gapping your plugs down to .8 before commiting to a set of splitfires or similar.

[mad082]

how old are the plugs that you are running? if they are getting on a bit then whack a new set in. even if they are iridiums and aren't that old (10-15,000k's) they may be dead.

does it sound like its hitting the speed limiter? i had a dead coil and when you boosted up it sounded like it was hitting the speed limiter (but would keep reving).

[l0WRB]

quote name='BHDave' date='22 Jul 2006, 08:52 AM' post='2348076']

For justin- you are probably on the edge of the r & r mapping and the cold denser air is tipping you over the edge. Combined with old coils you begin to get the miss as the mixtrues are richer. Check the heat range plugs you are running too. You want a 6.

I'd put it on a dyno before doing anything though and see what your arf's are doing. It will eliminate afm's/fuel pumps/fuel filters/injectors from the list of possibles for 60 bucks. Then start looking at spark.

Taso- your's is almost certainly coils, but try gapping your plugs down to .8 before commiting to a set of splitfires or similar.

ok mate i will give my mech a call and get him to throw it on the dyno and check those possibilities out

i know the timing is set at 15degrees advanced at 650rpm as we set it about 2 weeks ago because for some reason the timing was at 0 degrees on idle : ,fuel filter was changed when the car was complied about 8 weeks ago along with oil,i also put in a new walbro 500hp pump 3 weeks ago as stock one died on me. i wish i had a mate with a powerfc to plugin and find out but he lives 4hrs away! im running heat range 7 plug gapped at .8

[l0WRB]

how old are the plugs that you are running? if they are getting on a bit then whack a new set in. even if they are iridiums and aren't that old (10-15,000k's) they may be dead.

does it sound like its hitting the speed limiter? i had a dead coil and when you boosted up it sounded like it was hitting the speed limiter (but would keep reving).

plugs are only about 4 weeks old, i pulled out platinums that it came over with from japan

nah its not hitting speed limiter, ive felt that before it and its a jarring motion and basically pulls ur whole car back lol

[chrissso]

This is IMO absolutley ECU.

To back it up.

I have a Jaycar DFA - it's a air flow voltage adjuster that works like a safc.

The DFA has a switching mechanism that turns on the voltage regulation, only atfer the car has started.

I installed it and had it tuned and my car was going well, with no misfire. It had repaired colipacks and spark gapped at 0.8mm.

Anyway, one night, my car seemed sluggish at 10psi. This was at the start of winter this year. Then on cold nights, it would pop and fart and misfire etc.

After checking things out, I found that the adjustment for the DFA to kick in after the car had started was out, and not kicking in. The original afm voltage was being put though to the ECU. After recalibrating the DFA so it would kick, the car went better than ever, all problems solved.

It would seem that on cold nights, the air is denser ^whatBHDavesaid^ and your ecu dumps heaps of fuel in making the mixture rich. This will cause misfire. It's like a protection mode. Seems to happen with engines fitted with pods and intercoolers more frequently.

Now your colis might not be good enough, but I would think that if your colis are stuffed, you would get the misfire all of the time, and not just when cold.

So your solution IMO is to get an apexi Power FC Computer, or an apexi SACF2 , or build a Jaycard DFA. Then get whatever you pick tuned.

I also netted a 20kw or more gain with the DFA. If I get more money, (and I don't sell the skyline) I will be buying a Power FC from a group buy from the forum.

Chriso