Alright guys so i really wanted to try figure this out myself but not being that knowledgable on SR's im finding myself stumped. The engine spec is as follows: Sr20det rebored 0.5mm with wossner pistons Cosworth Head Gasket ACL Bearings Tomei 550cc's Tomei fuel pump Apexi Power FC with controller Blitz intercooler with hardpiping HKS GTSS Turbo Full 3 inch exhaust So initially the car had a hunting idle for a while but seemed to be running fine otherwise. Then a clutchdump in second bogged the car and since then the issue is a steady misfire on idle and in general a rough running engine that bogs bad on throttle and is misfiring its underivable. I started diagnoses and checked for vacuum and boost leaks but no sign. I then switched out the MAF, igniter chip, coils and plugs with a friends car and no improvement. I isolated the issues to cylinder 4 i think! there is no difference in running when i disconnect that coil but a significant change on all others. Inside that cylinder is quite black compared to the rest and the plug came out black but dry. I did a compression test (cold) and got the following (really low but all within 1 bar) can the low results be due to the rebore and HG? 4) 8.2 bar 3) 7.7 bar 2) 8.5 bar 1) 7.8 bar I then cleaned the intake and removed the fuel rail to check for leaks. I found a leaking injector on 4. I replaced the orings which stopped the leak so i put it all back but it still misses. Ive checked voltages, resistance on anything i could, all fuses, fuel pump, fuel filter and nothing still. There is no unusual smoke from the exhaust! I suppose this leaves valves :/ Anyone got any insight as to where i can go from here? Im pretty much out of ideas. Cheers
Well done on the diagnosis, you've covered off all the basics. I'd suggest a leakdown test to see if the chamber can retain pressure. Interesting that you found a leaking injector and fixing the leak didn't fix the problem. What fuel pressure regulator is on it? Factory or adjustable? Did you rebuild or was done by a previous owner? Are the injectors new or secondhand? And have you pressurised the intake system (from turbo intake to throttle body), it could be a hole in the intercooler
Cheers for the feedback man. The rebuild was done by the previous owner so i bought the car at its current spec. As far as i know the injectors were new when he got them but i cant say for sure! I have a short vid of the injectors working i can post a link to. They look to be clean no fan spray or irregular angles or anything. The fuel pressure regulator is stock but one strange thing i did notice was that with a fuel pressure gauge plumbed in after the filter that after initial prime on turning the key the pressure rises but then drops again immediately. This seems like the return valve in the pump possibly but wile the engine is running this shouldt really cause an issue should it as the fuel pump is always on?Can a fuelling issue really cause a dead cylinder ? I thought it would have caused issues right across the 4?With regards the boost and vacuum leaks i mainly searched for vacuum by spraying break cleaner everywhere i could think of but found nothing. I havnt tried pressurising the intake system yet but i can get access to compressed air so its something i will try in the next few days. The only reason i havnt tried it yet is that while running the boost gauge always reads exactly what it did before the issues started, am i stupid to go by that ?
No, if it's still making the same boost as before then it's not a boost leak (forget about pressure testing the intake), so either electrical, mechanical or fuel to go The fuel pressure dropping will be the FPR doing it's job and bleeding off pressure above it's set pressure. As long as it doesn't continue dropping??? As for electrical: grab a timing light and check the timing. Also see if you can swap on a known working CAS, or at least clean the terminals on the plug and refit. If that doesn't improve the situation, do the same with the TPS. Did you change number 4 spark plug once you found it blackened? Might be worth swapping the spark plug to another cylinder, and inspect for cracks too
Totally wrong. On SR20s with an airflow meter, ANY leak between the AFM and the actual cylinder head itself can cause it to run poorly.It sounds like a big boost leak to me on first glance, the very first thing i would have done is have a pressure leak test done on the entire intercooler pipework from the turbo to the throttle body. Check the AFM-turbo intake pipe for cracks, too. Eliminate the dump valve being a leak, if you have one, too.
Thanks again lads,Il pressurise the system because i have a compressor there but im going to have to come up with some way of attaching it to the intercooler piping which put me off initially.Ye Ben I swapped out all 4 plugs very early on in the diagnosis but cylinder 4 just keeps blackening them. This is one of the big reasons i was leaning more toward valve/ring issues. Can a boost/vacuum leak or fuelling really affect a singular cylinder so obviously ? I would have thought it would cause undesirable conditions over all 4 cylinders. Regarding the fuel pressure drop, it goes from full to zero in about 3 seconds after prime :/ seemed strange to me most lads on the forums seem to talk about fuel systems holding their pressure between the point of initial prime and engine start.
Because the fuel pressure is bleeding off quickly and it's still turning plugs black it sounds like injector 4 is still leaking Would check the surface of where the injector seats on the intake manifold for any foreign objects / damage. If nothing to be found then get them all flow & pressure tested You can connect air pressure to the intake system using PVC guttering end caps. There's a few vids floating around on Youtube on how to do it. Piss easy
Hows it going lads. Bit of a delay on this as i didnt get up to the shop but eventually got up and got a leak down test done and a boost leak test. Neither showed any cause for worry. The boost leak test did lead to finding something that im not sure about. The car is running on the stock bov and while pressuring the system air is pissing out of a hole that looks to be only about 1-2mm in diameter in the sidewall of the bov itself. Its definitely a drilled hole but doesnt look stock. Anyone know if this is stock? Ive pressurised the rail before it went back in the car and it all seemed fine but maybe it worth taking it out again and retesting.
Did you swap the coilpack wiring when you swapped the coils? And are all the earths for the coilpack wiring clean? Might pay to get it run up on a dyno and see if there's anything in the ECU causing the issue - Power FC's are known as the most hardy of all ECU's
So ye went through all the earths and swapped the wiring and ignitor chip and didnt fix anything. So the next thing is the car is going to go to a specialist and the map is getting checked out. Il check back in and update once that happens. Hopefully i can enlighten anyone else having similar issues after all of this.
So a quick update to this. The car went to a specialist last week and by adjusting the timing and fuelling he has gotten the car to the stage where it idles fine and drives fine off boost. It still misses on boost. He said the map was fine so he is now troubleshooting fuelling and CAS. Hopefully can update again this week.
Alright guys i know this is an old thread but there are some updates that i think might help others in the future. So since the last time the fuelling system has been given a bit of an overhaul. Lots of new lines up front, a regulator and permanent pressure gauge. This didnt actually fix the misfire however. As I had already tried a friends ignitor chip, coils and coil loom i didnt think it was possible for them to be part of the problem as they came from a perfectly running car, however new coils and a new ignitor were fitted and this enabled the car to pull fine again on boost like before. So now I have a drivable car!!!!! The problems are not all solved however. Although the car is perfectly drivable and pulls hard on 1.2 bar it still has persistent issues which im trying to resolve. Firstly when you turn the key to on just before ignition the apexi hand held controller registers 12.3V. Once the car is started the idle is quite lumpy and the battery light flashes. If its dark the headlights, rear lights and gauge cluster will actually brighten and dim in synchronisation with the lumpy idle. (Definite power issues) ! Once the car is driven 50m the battery light goes to solid on (no flashing) and the lights all round seem to go back to normal however the Apexi now registers around 15V constant. When the car then gets to operating temp around 80-90 degrees the last curveball is thrown in when a hunting idle begins constantly from 1100-1200 over and over. Another strange side note is my 12v constant that should keep my gauge clock right and goes into my radio is no longer working im getting 3v on it and the radio has stopped even turning on! (More electrical fun! - Is it linked???) So to finalise i am starting to wonder if the problem all along has been electrical. When the car is first turned on and the battery and power seem to be at their craziest thats when the lumpy idle/misfire is still present. As soon as the car is driven and the power is increased the idle smoothens out but eventually starts to hunt but i think that might be unrelated as i had that issue back before the misfire. IACV maybe? Any thoughts on this would be appreciated as electronics and me dont get along so any heads out there with some previous experience feel free do give a bit on input. For any Germans out there the car will be at Reisbrennen this weekend
Sounds like alternator regulator to me, not allowing consistent voltage. Any auto sparky should be able to check it easily
