cosecon Posted July 30, 2012 Share Posted July 30, 2012 Hi to all I have a Defender 90 manual fitted with a cross bolted V8 4.0L. The cylinder heads are original 3.5 carb, but skimmed accordingly for composite gasket fitting. The heads are quite extensively ported. I currently have hotwire EFI installed and Megajolt. My engine performs very nicely in all rev range. I have a 2 small but annoying problems, which I had with the distributor also: On idle, I have normal 700rpms with a small variation of +-25 rpm, but it feels a bit shaky. (rough). It is like when I had carbs and the choke was applied in a warm up engine, but no black smoke and emission testing in idle is ok. My advance in idle stationary is 13 BTDC and engine load (vacuum is 45Kpa). Yesterday I readjusted the base idle as per manual and I was able to go down to 480 rpm with the engine not stalling. I readjusted up to 525+-25 as per manual When cruising with 1000-1500 rpm, with the foot just touching the throttle, you get this shaky feeling. If you just press a little more the accelerator, It is perfect running. My belief is that both problems are related. So far I have tried: to replace with spare Throttle pot to replace with spare Idle valve to replace with spare AFM (but both I have are not “known to be working”, they were bought on EBAY) to decrease fuel pressure (I have and adjustable regulator) things got worse. Connected several time to ecu fault reader with no faults. I would like to inform you that I have a speed transducer connected, I have a manual box and no oxygen sensor with proper tune resistor. Before , i had a webber 4barel with lucas distributor with no such problem. Is it possible that the K&N cone filter I have directly connected to the AFM is “confusing “ the air flow meter with pulse air in low load/rpm? What do you believe I should check? Thanks P.S. I know the answer is megasquirt, but I would like to postpone a few months for "funding" of MS Quote Link to comment Share on other sites More sharing options...
muttleyd Posted July 31, 2012 Share Posted July 31, 2012 Are you sure with the parts swapping you have not got an air leak. You wouldn't notice that at higher speeds but would cause poor low speed running. Be surprised at 1500 cruise though. Good luck Quote Link to comment Share on other sites More sharing options...
cosecon Posted July 31, 2012 Author Share Posted July 31, 2012 Are you sure with the parts swapping you have not got an air leak. You wouldn't notice that at higher speeds but would cause poor low speed running. Be surprised at 1500 cruise though. Good luck Vacuum at idle is 45Kpa (megajolt). How does this look for a v8? On the low or the high side? Quote Link to comment Share on other sites More sharing options...
Dave W Posted July 31, 2012 Share Posted July 31, 2012 On the face of it I'd say you're advance is a bit high for idle and that may be contributing to the problem. Have you checked the advance with a timing light and ensured the timing marks are correct ? Just to rule it out as a source of problems, warm the engine up and while it's idling disconnect the 4 way plug from the idle air control stepper on the RHS of the plenum. See if that makes any difference to the stability of the idle and also to the low rpm cruise problem. Quote Link to comment Share on other sites More sharing options...
cosecon Posted July 31, 2012 Author Share Posted July 31, 2012 On the face of it I'd say you're advance is a bit high for idle and that may be contributing to the problem. Have you checked the advance with a timing light and ensured the timing marks are correct ? I have confirmed TDC marks and my vr sensor is less than half a degree out. I have tried several different advance settings, including 8, 10, 12 degrees with no luck, that is why I sort of ruled out ignition. Just to rule it out as a source of problems, warm the engine up and while it's idling disconnect the 4 way plug from the idle air control stepper on the RHS of the plenum. See if that makes any difference to the stability of the idle and also to the low rpm cruise problem. I will test this, although I doubt it since I have also tried a spare Idle air control stepper. It is not that I have a bad idle, it is ok but just not perfect. I just had another thought... I checked for vacuum leaks everywhere....except injector o-ring to manifold....What if I have some leak at any of the injectors? Quote Link to comment Share on other sites More sharing options...
V8 Freak Posted July 31, 2012 Share Posted July 31, 2012 Silly question but have you cleaned / gapped the plugs or tried new? Have you systematically replaced HT leads to see if one failing to deliver a spark (Would notice it far more at low RPM) Quote Link to comment Share on other sites More sharing options...
Quagmire Posted July 31, 2012 Share Posted July 31, 2012 My 3.5 runs at a 30kPa idle at an idle speed of 850rpm. Thats a bog standard. 9.35:1 compression engine. I wouldnt worry too much about it as any rough running will give you a higher kPa figure. Quote Link to comment Share on other sites More sharing options...
AncientGeek Posted August 1, 2012 Share Posted August 1, 2012 No-one has mentioned it, so have you tried measuring the voltages coming out of the MAF? The low rpm mixture on the MAF is adjustable, pretty much like the idle mixture screw on a carb. Theoretically you need a CO meter but you can do it by ear using the lean drop method. There is plenty of info on the web about how to do this and which wires to measure. 45 Kpa is a bit high but within limits. 13 BTDC is OK with a megajolt, imho. You can even go higher. Quote Link to comment Share on other sites More sharing options...
cosecon Posted August 2, 2012 Author Share Posted August 2, 2012 Silly question but have you cleaned / gapped the plugs or tried new? Have you systematically replaced HT leads to see if one failing to deliver a spark (Would notice it far more at low RPM) Spark plugs brand new, changed 500miles ago HT leads Brand new (installation of megajolt) No-one has mentioned it, so have you tried measuring the voltages coming out of the MAF? The low rpm mixture on the MAF is adjustable, pretty much like the idle mixture screw on a carb. Theoretically you need a CO meter but you can do it by ear using the lean drop method. There is plenty of info on the web about how to do this and which wires to measure. 45 Kpa is a bit high but within limits. 13 BTDC is OK with a megajolt, imho. You can even go higher. CO adjusted on a high tech analyzer. AFM values are a little less than expected. 1.45 volt in idle instead of 1.6 idle. Tested a second used ebay afm and similar values. I suspect vacuum leak (45Kpa looks a bit to the high side) but not possible to find .... I tried spraying carb cleaner even on the injector holes on the manifold but no leak... Quote Link to comment Share on other sites More sharing options...
Julian Posted August 2, 2012 Share Posted August 2, 2012 Spark plugs brand new, changed 500miles ago HT leads Brand new (installation of megajolt) CO adjusted on a high tech analyzer. AFM values are a little less than expected. 1.45 volt in idle instead of 1.6 idle. Tested a second used ebay afm and similar values. I suspect vacuum leak (45Kpa looks a bit to the high side) but not possible to find .... I tried spraying carb cleaner even on the injector holes on the manifold but no leak... I know very little about this installation of yours as Rover V8 have never been something I've got my hands on. I did have a very similar problem to this once on a big block Mopar and it was an air leak, between inlet manifold/valley pan and crankcase. I discovered this by noticing how much crankcase vacuum was being created even with the breather hoses disconnected/blanked. One little trick that I learnt when setting up idle mixture on 4 bbl Holley carbs is to introduce some propane gas (via a blowtorch) into each primary in turn - you can then instantly determine if the mixture is rich or lean on each side and adjust each screw accordingly. Julian. Quote Link to comment Share on other sites More sharing options...
cosecon Posted August 3, 2012 Author Share Posted August 3, 2012 After checking all, I reached the conclusion of faulty Air Flow meters. I tried a 3rd one from a friend and I had much better and smoother operation than before. I also found out that when my 2 AFMs are cold (not the engine, just newly installed afm on a warm engine) it is working nicely. Once the afm heats up....it looses accurate performance.... I guess I will accelerate the megasquirt installation. I am not worried about cabling...I am worried about fuel maps (spark maps I already have...) I guess if I am stuck I can always send air tickets to a "Grown Up" for a free weekend in Greece.... Quote Link to comment Share on other sites More sharing options...
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