Ian C Posted March 10, 2004 Share Posted March 10, 2004 Just to update those who have been following this and helping me out a bit, I've got all the bugs fixed that cropped up while doing the problem solving and now I have a repeatable scenario. Really I'm after people who know about ECU's, mapping standalone and stuff, so that they can tell me what the ECU is up to at certain points and what sensors it uses to do these things, otherwise I'm flailing around in the dark really. There are two symptoms, one is a grotty cold start, the other is a lift-off stall problem when warm. Grotty cold start - the car fires up at 1100rpm as it should do. After about 5 seconds the idle drops rapidly to about 650rpm and it sits there having a hard time - missing beats, sometimes making a nasty clattery noise like it's seriously overfuelling - which it is. Whether that's overfuelling or under-airing I don't know. Funny thing is, at a point in the cold start warmup sequence it seems to realise something is wrong and starts to increase the idle speed and sound healthier until it gets to the rpm it should be at for that engine temperature, and then lower the rpms as per normal. I drew a piccy to illustrate this: http://www.ian.chisholm.clara.net/pix/idle.gif The green line is what the idle-warmup sequence should be like from my experience. The red line is what I'm getting now. I assume there is an ECU strategy for the initial startup idle, one for dropping the idle as it warms up, and one for warm-engine idling. Howver, I don't know this for sure - can anyone shed light on this? Liftoff - stall symptom - I lift off the throttle and the car chugs while in gear like it's missing beats. If the clutch is in, the revs drop to about 1000rpm, pause there a bit, and then plunge to below 500rpm. At this point the ECU tries to recover things and if it does, settles to a steady idle at about 650-700rpm. This is intermittent, sometimes it catches the idle at 700rpm without dropping any lower. Sometimes it stalls. One extra thing of note is that opening the throttle everso slightly and slowly will cause a stumble in the idle, and I *think* this is the point where the throttle position sensor's "idle" switch disconnects. I'm trying to narrow down what the hell the ECU is doing when these things are going on so I can figure out what systems could be at fault. Any thoughts are welcome. -Ian Quote Link to comment Share on other sites More sharing options...
dude Posted March 10, 2004 Share Posted March 10, 2004 Ive got a UK doing this at the moment , its just had a HKS BOV fitted allthough the guy says it did it a few time before !!! Dude:flame Dev Quote Link to comment Share on other sites More sharing options...
Dragonball Posted March 10, 2004 Share Posted March 10, 2004 So it's basically the open loop period prior to the O2 sensor warming up? Quote Link to comment Share on other sites More sharing options...
Guest Terry S Posted March 10, 2004 Share Posted March 10, 2004 Ian, the AFR during warm up is normally between 0.8 and 0.9 stoich. The ecu does this as part of the cold start map. It sounds like the extra fuel is not being added for some reason. The ECU works off water temperature to determine the cold start period. Maybe a faulty water temp sensor or connection? The ecu will also have an enrichment multiplier during cold start, but unless the ECU is fubar like we discussed yesterday, there is no reason for this to have altered. Have you got an O2 bung welded in you DP that is easily accessible? Quote Link to comment Share on other sites More sharing options...
eyefi Posted March 10, 2004 Share Posted March 10, 2004 i'd agree, it sounds like coolant temp sensor, but that doesnt seem to add up with the lift off stall. did u try another ecu? have u tested the idle switch signal? Quote Link to comment Share on other sites More sharing options...
Guest Terry S Posted March 10, 2004 Share Posted March 10, 2004 It does point towards the ecu. There will be a decel recovery time programmed into the ecu, which is the time before the ISCV take over on lift off. If this time is too much it will cause the symptoms Ian is experiencing, but I can't see why a stock ecu would play up like this. Bad earths have very strange effects on ECU's but I am sure Ian has checked that. Quote Link to comment Share on other sites More sharing options...
Wez Posted March 10, 2004 Share Posted March 10, 2004 Do you have a stock ECU or an aftermarket one, if so which one? Quote Link to comment Share on other sites More sharing options...
Guest Terry S Posted March 10, 2004 Share Posted March 10, 2004 Wez it's a stock ecu;) Quote Link to comment Share on other sites More sharing options...
Wez Posted March 10, 2004 Share Posted March 10, 2004 OK cool, I was wondering because the bucking on lift off was what needed fine tuning on my AEM. Basically when you lift off and go into vac the base map did not have a low enough voltage set for the MAP sensor and was therefore dropping off the fuel map and bucking, once this was adjusted and fuel map tuned I never had another problem with it. This sounds similar but strange on the stock ECU, could check the map sensor for dirt etc. Quote Link to comment Share on other sites More sharing options...
eyefi Posted March 10, 2004 Share Posted March 10, 2004 my ecu has adjustment maps for air intake temp and coolant temp vs fuel, also rpm and MAP pressure. id sart looking at them inputs on the ecu when it starts to dip. if u turn on the lights and ac will it still do it? Quote Link to comment Share on other sites More sharing options...
Ian C Posted March 10, 2004 Author Share Posted March 10, 2004 Wow, thanks all for the flurry of responses! I'm trying to blag another 6spd manual ECU to test it but it would be a really odd way for an ECU to blow up - altering it's map, hmmm. Dubious but worth a try! I've swapped the MAP sensor out already, no change there - it's reporting the right numbers to the Apexi AFC as well. I've got a coolant temp sensor to try, gonna plumb that in now. As well as another intake air temp sensor and a throttle position sensor. Desperate, moi? If I knew more about the voltages the O2 sensor reported back I could diagnose what's going on with the cold start a bit more, at the moment the O2 sensor just builds up from 0.0v to about 0.6v steadily, at that point the idle picks up as shown in the graph but the O2 voltage keeps on steadily climbing to 0.9ish v. -Ian Edited to add - eyefi, yes, with the lights and aircon on it still chugs but it stands a better chance of not stalling because the base idle is raised higher. So all the symptoms are still there. Quote Link to comment Share on other sites More sharing options...
eyefi Posted March 10, 2004 Share Posted March 10, 2004 i cant check my stock o2, cos im in bits at the moment, but IIRC mine was jumping up and down all the time, not steady at all. i cant remember what it did at cold start tho Quote Link to comment Share on other sites More sharing options...
Wez Posted March 10, 2004 Share Posted March 10, 2004 That steady voltage climb for a stock O2 sensor doesn`t sound correct, the stock O2 should be jumping about between 0 - 1V as the fueling is constantly adjusted. Quote Link to comment Share on other sites More sharing options...
Ian C Posted March 10, 2004 Author Share Posted March 10, 2004 Mine sits at 0.92 to 0.94v once the engine is warm. When I rev up and let go it stays at 0.9v going up the revs and goes down to anywhere from 0.8v to 0.5v as it sputters it's way back down. I've swapped the intake air temp, coolant temp, and throtle position sensors, no change in behaviour. If I add extra air into the system by disconnecting a hose on the intake manifold, the idle speed increases but it still stumbles on liftoff, so that's just masking a symptom rather than helping. I've watched the ISCV's stepper-motor-controlled stopper and on liftoff it opens up to let more air flow as the idle point is reached, and then closes up again quickly. I think that's just a 'blip' to catch the revs and stabilise them, so *that* appears to be doing what it's supposed to be doing too. I've cleaned up and already-clean earth point that earths all the ECU and sensors. Revving up is fine. Holding revs for cruising causes slight 'missing', but it doesn't feel like a misfire. Closed loop stuff? Could a dodgy O2 sensor be doing all this? I've tried another one but hey. And who lives near Norwich and has a j-spec manual ECU I can swap in for a couple of minutes? -Ian Edited to say - I was checking all the diagnostic port readings, and the FP pin sits at 8.6v but drops to 8.1v as the engine stumbles, then goes back to 8.6v as it recovers. This appears to be something fuel pump related - is this worth following up? Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted March 10, 2004 Share Posted March 10, 2004 Ian, I'm going up to Woodbridge on the 21st, which isn't a million miles away from you. Alternitively, my wife has just suggested we come up to you on Sunday Quote Link to comment Share on other sites More sharing options...
Ian C Posted March 10, 2004 Author Share Posted March 10, 2004 Free cups of tea and food if you do Bring multimeters and magic fairy dust and sacrificial chickens -Ian Quote Link to comment Share on other sites More sharing options...
Matt Harwood Posted March 10, 2004 Share Posted March 10, 2004 Multimeters aren't a problem, the magic fairy dust is currently on backorder, but I may be able to nick a bit from my 7 year old daughter. The chickens we can get from Tesco's, pre-sacrificed! Quote Link to comment Share on other sites More sharing options...
JohnK Posted March 10, 2004 Share Posted March 10, 2004 For what its worth, Chris Wilson once told me you would need an ociliscope to do proper diag of the O2 sensor. Quote Link to comment Share on other sites More sharing options...
Ian C Posted March 12, 2004 Author Share Posted March 12, 2004 Additional info. 16mpg. Normally get 21mpg driving more enthusiastically than I have been. So, it's overfuelling then -Ian Quote Link to comment Share on other sites More sharing options...
richardharmon Posted March 12, 2004 Share Posted March 12, 2004 I’m prepared to be shot down in flames for this suggestion, but since no one has mentioned it! Could it be something as simple as a sticking injector? If it is sticking open sometimes that could account for rough idle, bad cruise and lack of symptoms under higher engine load (because it’s open for longer anyway so the effect of sticking is less noticeable)? Anyway that was just a thought I had while reading the thread, probably nonsense, just had to get it off my chest. Quote Link to comment Share on other sites More sharing options...
jagman Posted March 12, 2004 Share Posted March 12, 2004 sticky injector, sounds feasable to me-I guess youll have to pull the plugs,and check for the one which is black as your hat Quote Link to comment Share on other sites More sharing options...
Ian C Posted March 12, 2004 Author Share Posted March 12, 2004 Hey, any suggestions are welcome Alas, all six plugs are black as the hat I don't own Plus once warm the idle is ok-ish. The odd variance in rpm, +/-50. -Ian Quote Link to comment Share on other sites More sharing options...
richardharmon Posted March 12, 2004 Share Posted March 12, 2004 Another thought then, have you checked your fuel rail pressure is what it should be, it's not way too high? Though I guess the closed loop system should take care of that situation? Quote Link to comment Share on other sites More sharing options...
Adam W Posted March 15, 2004 Share Posted March 15, 2004 Ian, I've just thought. If you have an SAFC or similar altering the signal from the MAP sensor to the ecu, try taking it out of the loop and see what happens. My SAFC looked like it was working and I thought I had a knackered airflow meter, turns out the SAFC was seeing a signal from the engine but the ECU wasn't seeing a signal from the SAFC! Could be something similar? Quote Link to comment Share on other sites More sharing options...
Ian C Posted March 15, 2004 Author Share Posted March 15, 2004 Adam, I have tried removing it from the loop already My ECU ran Matt's car OK, so it's not that. Matt will attest to the freakish behaviour that I'm seeing and also the existence of the loud click as I open the throttle - which coincides with the engine stumbling. Hmm. After yanking the lead off injector #6 while the engine was in a warmed-up idle state, the idle didn't really change. Plugging it back in and removing #2 the idle... picked up . Plugging back in #2 and the idle went to 2000rpm and still did it after an ECU reset Thanks to Matt for coming all the way up to see me on Sunday, witnessing the enigma that is my car, and for rewiring my airflow wire - I'm *sure* it must have been loose and he didn't simply break it -Ian Quote Link to comment Share on other sites More sharing options...
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