Lump Posted October 15, 2011 Share Posted October 15, 2011 I've replaced the V8 in my car with a later model jaguar inline 6 (AJ6 from an XJ40 or XJS) I've got it running and have been for a few test drives, its runs great except for a few idling problems 1) Engine idles at 1100 cold and 1000 hot (the tach is calibrated for a V8 so I'm guessing thats about 1400 and 1250 actual - should be around 900 and 700) 2) When reved from idle the engine will return to idle then rise to about 1500 and then slowly return to idle again. If I disconnect the idle stepper control motor - the base idle will be 1500 but when reved it will still drop to around 1000 and rise back to 1500 and stay there. So far I've checked the throttle position sensor (OK) the throttle butterfly opening (OK) the MAF sensor (faulty and replaced but no improvement). The ignition is controlled by the ecu from a crank position sensor (could a badly positioned distributor cause this?) I have found out how to reset the idle speed but I get the feeling its a symptom rather than a cause - any ideas on what I should be checking out? Quote Link to comment Share on other sites More sharing options...
keltik Posted October 15, 2011 Share Posted October 15, 2011 Vacuum leak or badly set timing is my guess. Quote Link to comment Share on other sites More sharing options...
anglia4 Posted October 15, 2011 Share Posted October 15, 2011 I would guess a vacuum leak. Get a hose and with the car idling listen through the hose to different points around the intake and associated hoses, you will be able to hear the sucking quite clearly where there is a leak. Another way of finding a leak I have heard is by spraying carb cleaner(?) on the different gasket joints etc in the manifold and the revs will rise if it sucks the cleaner through. (Haven't tried this one myself) Quote Link to comment Share on other sites More sharing options...
Yowzer Posted October 15, 2011 Share Posted October 15, 2011 Vacuum leak Quote Link to comment Share on other sites More sharing options...
Dell'orto Posted October 15, 2011 Share Posted October 15, 2011 Another way of finding a leak I have heard is by spraying carb cleaner(?) on the different gasket joints etc in the manifold and the revs will rise if it sucks the cleaner through. (Haven't tried this one myself) Use engine start, carb cleaner wont do much unless its a big leak, in which case it'll die. Quote Link to comment Share on other sites More sharing options...
efp0wa Posted October 16, 2011 Share Posted October 16, 2011 I'm more clued up on Nissan and Honda EFI motors but in my experience the symptons you describe often point to a dirty/blocked or faulty idle control valve/IACV valve. Quote Link to comment Share on other sites More sharing options...
Spencer Posted October 16, 2011 Share Posted October 16, 2011 yea the main candidates would be a vacuum leak, Blocked/faulty idle control valve, or possibly the idle control valve is wired up incorretly which happends with allot of conversions Quote Link to comment Share on other sites More sharing options...
Lump Posted October 24, 2011 Author Share Posted October 24, 2011 Well I've had no luck finding any vacuum leaks - either just by listening or with a can of starting fluid , I've also cleaned out the idle stepper motor without any effect. I'll try re-setting the base idle and see if that fixes anything Quote Link to comment Share on other sites More sharing options...
Spencer Posted October 24, 2011 Share Posted October 24, 2011 I have no idea about your specific EFI setup, but with allot of EFI setups the ECU needs to be wired in a way that it controls the relay for the stepper motor. This is to be sure that the motor is always set at a reference point the next time the car is started. Something to check anyway Quote Link to comment Share on other sites More sharing options...
Lump Posted October 31, 2011 Author Share Posted October 31, 2011 I have no idea about your specific EFI setup, but with allot of EFI setups the ECU needs to be wired in a way that it controls the relay for the stepper motor. This is to be sure that the motor is always set at a reference point the next time the car is started. Something to check anyway I don't think its the wiring to the stepper motor as its all part of the the engine loom - which is nicely standalone on these vehicles. I set the base idle as low as possible this morning (about 1000 rpms - rev counter recalibrated, should be lower but it wouldn't go lower) but the single surge on returning to idle is still present There is another air valve on the inlet manifold similar to the stepper motor, it has two coolant feeds running to it which I assume open or close a valve depending on there temp. I can lower the idle by pinching the air hoses leading to this. I can't find this thing mentioned in the manual - does anyone know what its called? - and will messing with it help? Quote Link to comment Share on other sites More sharing options...
Lump Posted November 10, 2011 Author Share Posted November 10, 2011 thanks for the suggestions guys, a few days after resetting the idle speed it stopped its surging behaviour. so i guess the ecu has figured out what its trying to do with the engine speed. Its still idling a bit high so I'm going to get someone to have a look at it this week. Big plus though it that it passed it cert test this week, so I'm just waiting for the plate to arrive to get a new warrant on it Quote Link to comment Share on other sites More sharing options...
KKtrips Posted November 10, 2011 Share Posted November 10, 2011 As a side note what did you do with your old V8? I assume it was a Chev? Quote Link to comment Share on other sites More sharing options...
Lump Posted November 13, 2011 Author Share Posted November 13, 2011 As a side note what did you do with your old V8? I assume it was a Chev? Yup it was a 350 Chev. I sold it to a mate of a mate whose putting it into a J1 bedford Quote Link to comment Share on other sites More sharing options...
Ranter Posted November 13, 2011 Share Posted November 13, 2011 Jo Bedford? Must be the same one, he said it was from a Jag. Started it up last weekend, ran well. Quote Link to comment Share on other sites More sharing options...
Lump Posted November 13, 2011 Author Share Posted November 13, 2011 Sounds like the one. I was wondering just the other day how they were getting on with it. Did they fix the trans or just replace it. Quote Link to comment Share on other sites More sharing options...
Ranter Posted November 14, 2011 Share Posted November 14, 2011 I think its still on there for fitting purposes but there is another one for it in case. Its not ready for driving just yet but we couldn't resist firing the engine up. What was wrong with your one? Quote Link to comment Share on other sites More sharing options...
Lump Posted November 14, 2011 Author Share Posted November 14, 2011 Basically it lost all forward and reverse gears. I think the internal pump was the problem (fluid level doesn't drop when gears are selected). I already had most of the bits I needed for my engine swap when it blew so I didn't investigate it too closely Quote Link to comment Share on other sites More sharing options...
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