Nissan 200SX Club - South Africa

thanks calibrator.

i didnt think that the car would not be driveable with a knock map engaged. its very strange - i've never seen anything like it.

we have checked the fuel pressure while the car exhibits the symptoms, and its normal. the spark seems to be ok, because it idles fine.

its basically at any point above the throttle resting position that it will not rev up. also the "whap whap" symptom (i have no other way to describe it) is one that is very regular. it has a beat, a rhythm. whap then pause then whap then pause. while its "whapping!" it sounds like a normal engine running on four cylinders. the pause part sounds like an engine turning but not combusting any mixture.

caver - would you be willing to do a dyno tune without keeping the car for too long? i mean like about 2 or 3 working days?

A dynotune or piggyback normally takes a day unless there are issues.

The Calibrator wrote:A dynotune or piggyback normally takes a day unless there are issues.

Just not tomorrow or even Friday!

why sqwerty? you got him all booked up then????

lol - i think i might have found the problem. well - i hope so. found a 12v supply wire that goes to coil pack #1 was spliced, then something added (probably immobiliser or something), then that something was removed.

in order to reconnect the wire after it was removed, the fukkas solder bare copperstrand to each end of the splice and twisted them together. that was then taped up.

but it has a home right on top of the tappet covers!!! so it gets hot, the tape's glue melts and it unravels itself, and then the 12v makes intermittent contact with the grounded tappet cover, shorting the circuit out.

i tried shooting timing while the problem was there, and during idling you can see the strobe light flashing, and when you rev up the timing light only flashes momentarily - and only when the engine makes the "whap" sound like its about to rev up.

but the strobe stops flashing completely, until it goes whap again!!!

so its like this "whap (flashing strobe) ... nothing (no flashing strobe)... whap (flashing strobe)... nothing ( no strobe) and so on and so on!!!!

but i will remove the engine harness today, to see what other nasty surprises lie waiting for me.

i used to think it was murphy - now i'm begginning to seriously dislike the previous owners, and previous owner's mechanics, of my car!!!!!!!

found more cockups with my harness!

its obviously tired from the 270 odd thousand kilometers, and from being on top of the cylinder head and near to the turbo.

the insulation on many of the wires is totally cooked. its brittle and tends to break right near the connecting plug. that means there is exposed 12v wire right next to exposed ground wire on coilplug one for instance!!!

and there are a few plugs like that. the water temp sender plug was only connected with one single strand of copper, the rest of the wire had broken off.

all of the exposed wire had corroded too, and were a green rusty type of colour.

basically it offered no more heat or electrical insulation!!!

once i've rewired, i really hope that the problem goes away, otherwise we can have a bring and burn braai. we can cook a couple of steaks on top of my burning ca18det!!!

I hope you get your problem solved VC....I'm holding thumbs.

looks like i'm in for the long haul draco.

doing my time, paying some school fees along the way!

i ripped out the engine bay harness. the one that goes runs from the computer box. i checked all wires for continuity, and rewired those wires that were brittle and old. also fixed connectors where possible etc, etc.

put it back.

and guess what...

the problem is back.

i've now troubleshooted so much that i am totally disheartened!

i've had it running on a different computer box, no difference.

different MAF, same problem.

different TPS, same problem.

different combinations of the above, same problem.

i dont think it is the coils or injectors, because it is still idling fine.

i do get a strong fuel smell while trying to rev over 1500rpm and it starts missing, so the coils aren't firing intermittently. i checked the coil harness with a timing light - and all signal is lost intermittently.

i've checked fuel pressure while driving, and under boost, before the problem occurs its fine. its at about 36psi on full vacuum, and moves up to about 45-50psi under full boost.

so i'm convinced its electrical, and somewhere along the following flow diagram something is going wrong:

CAS + TPS => Computer Box => Power transistor => Coils => plugs.

CAS = i'm not sure if its this because i dont have a replacement to test with. but the car drives fine while cold, and idles fine while hot.

TPS = i've replaced this with another used one, and i still get the same symptoms.

Computer = i've replaced this with another used one, and it still has the same symptoms.

Power transistor = i've replace this with another used one (that was cold at the the time) and i get the same symptoms.

Coils = i havent replaced these while the symptoms show, but i could. i'm not convinced its them though. the car idles fine while hot, and if i use a timing light on the trigger harness for coil #1 i momentarily lose power at the exact time that the misfire happens. and that happens on each coil too.

plugs = i've changed these to the old ones i used to use because the new ones were terrible. the old ones worked well on the ca18. they are gapped to 0.8mm ATM. and are displaying spark when held outside the bay. hte car also idles fine.

so somewhere i'm experiencing a loss of signal when the car, or one of its components gets very hot.

anybody???

Gees VC you have basically checked everything, I hope someone has some advice...I don't have a clue....

forgot to mention that i got some strange readings when checking earths, both body and engine earths.

on the copper strand it measured 0.3 ohms - but on the connector 3.0 ohms!

so i fixed that thinking that a stupid earth disconnection had got the better of me. but i still got the problem.

then i noticed that the relays for "ign coil", "EGI" and were getting very hot in the engine bay. there is one right next to that for something called "N&P" (???) which was warm, but not too hot to touch for more than a few seconds!

i dunno - can a relay work when its cold, and then fuck out when its hot???

Jeez dude, I hope you come right. Have you tested with another coil igniter? (Dunno if this is the "power transistor" you've mentioned)

thanks sokar,

its the same thing. i drive around until i get the problem, usually when things are VERY hot.

then i change the ignitor, while trying to avoid 3rd degree burns from the turbo. and the problem persists!!! so i swop the hot one with a cold one, and get the same symptoms!!!

its mind boggling i tell you.

So have you eliminated the Knock sensor as the problem?

Daniel wrote:So have you eliminated the Knock sensor as the problem?

i have. we were getting that code on the ecu. i removed it to check that it was operating properly. and it is.

we are also no longer getting taht code as a problem on the ecu. its now 55 (everything OK) all the way!!!???!!!

veecee wrote:CAS = i'm not sure if its this because i dont have a replacement to test with. but the car drives fine while cold, and idles fine while hot.

Phinx has a SPARE CAS for you to TEST with (i.e. he definately wont part with it) PM Him, he might be going to wesbank on Wednesday. If you chat nicely to him he has other extra's of a spare motor he'll let you test with (Knock sensor, water temp sensors etc...)

I suspect you are all barking up the wrong tree.
Have you checked the mixtures before and during the"missfire"?
What is happening to to the injector open period when the issue starts?

You have checked a fair bit of stuff however this is one where experience comes into play.
Remember, Om te meet is te weet.