irregular popping!!!

[autocross7]

Okay... other than the fact that I am getting ticked looking for a coolant leak that I can not trace...

My 88 turbo has developed an irregular popping (miss-fire). It does not matter if the RPM is idle or wide open. I have pulled the plugs and they are fine: a little brown and no black carbon or ash on the electrode or insulators. The are about 100 miles new. I have also pulled the distributor and checked points and cleaned in general. Did not find any traces of carbon streaks, moisture, or anything else to suggest a problem. The ECON light seems to be opperating correctly as well - kicks in about 1800 RPM +/-.

I do not feel any power loss, but the popping is driving me nuts!!! Please help with ANYTHING I can check. I suppose the fuel system could need some calibrating??? I do not know much about the K-jettronic injection system except that they are "nearly bullit proof" according to most shops.

Drive topless!!!
Cameron

[lotusguy]

autocross7 said:

Okay... other than the fact that I am getting ticked looking for a coolant leak that I can not trace... My 88 turbo has developed an irregular popping (miss-fire). It does not matter if the RPM is idle or wide open. I have pulled the plugs and they are fine: a little brown and no black carbon or ash on the electrode or insulators. The are about 100 miles new. I have also pulled the distributor and checked points and cleaned in general. Did not find any traces of carbon streaks, moisture, or anything else to suggest a problem. The ECON light seems to be opperating correctly as well - kicks in about 1800 RPM +/-. I do not feel any power loss, but the popping is driving me nuts!!! Please help with ANYTHING I can check. I suppose the fuel system could need some calibrating??? I do not know much about the K-jettronic injection system except that they are "nearly bullit proof" according to most shops. Drive topless!!! Cameron

Cameron,

Popping is usually associated with a lean condition, whereas Spitting is usually associated with a rich condition.

The first thing I would suspect is an air leak around the isolators from the trottle bodies to the intake manifold. These use rubber 'O' rings to seal and therefore should not be drawn up tight. Instead, you must tighten them only so a gap of 3/16th" or so remains between them. The best gauge is to insert a 3/16th' drill bit between the gap and tighten until you can just extract the bit. One caveat, if overtightened, even once, the 'O' rings will be ruined requiring their replacement as they will leak from thereafter. They will also degrade with time becoming hard and lose their seal. Also, you NEVER want to put any weight on the carbs (if so equipped), throttle bidies or plenum, such as when working over the engine, as this too will cause them to lose their seal. It is a natural tendency place to place one's weight on the plenum box and such, but you need to consciously avoid doing so. Once they leak, they allow additional, unmetered air to enter the A/F mixture, altering it toward a lean condition. Have you or someone else been fiddling over the engine lately..??

But, before I would go tearing off the throttle bodies and plenum to replace them, I would first rule out a faulty O² sensor. If original, it's probably not a bad idea to replace it anyway. If faulty, this can falsely signal the duty meter that the engine is running rich, forcing it to lessen the quantity of fuel introduced creating a lean condition.

Finally, you could have clogged injectors, precventing them from delivering the fuel quantity called for.

Since you pulled the plugs and found them to be light brown, while this is ideal for a N/A car, it's actually a little lean for a Turbo car. Ideally, you want to see dark brown even to just black, but with no soot buildup or liquid on the plugs. Turbos need to run a little rich to avoid going lean once the Turbo kicks in, but before the increased fuel flow takes effect. Hope this helps. Happy Motoring! Jim'85TE



>> Edited by lotusguy on Wednesday 1st October 16:59

[autocross7]

As usual Jim... you are a wealth of Lotus knowledge!! A couple of us have been working over the top of the engine latly attempting to trace that d%*&# coolant leak that seems to be comming from nowhere! I'll check the O2 sensor... but I'd bet you have hit the nail on the head and there is air getting into the intake. I always try not to put any weight on the intake parts (as I have been told before that this is not good), but I can not say it was not done in the last two weeks!

However, I am not familiar at all with "the isolators from the trottle bodies to the intake manifold" being rubber or exactly where the 'O' rings described are located. As far as I can see, all of the gaskets from the plenum,throttle boddies, and intake manifold are a paper like substance...? My Lotus parts manual does not show anything that I think resembles what I'm looking for here... A little help for a "newby" at the Lotus game... where exactly are these "O" rings located? I'll check the O2 and get back to you!

Drive topless!!
Cameron

>> Edited by autocross7 on Thursday 2nd October 01:56

[lotusguy]

autocross7 said:

As usual Jim... you are a wealth of Lotus knowledge!! A couple of us have been working over the top of the engine latly attempting to trace that d%*&# coolant leak that seems to be comming from nowhere! I'll check the O2 sensor... but I'd bet you have hit the nail on the head and there is air getting into the intake. I always try not to put any weight on the intake parts (as I have been told before that this is not good), but I can not say it was not done in the last two weeks! However, I am not familiar at all with "the isolators from the trottle bodies to the intake manifold" being rubber or exactly where the 'O' rings described are located. As far as I can see, all of the gaskets from the plenum,throttle boddies, and intake manifold are a paper like substance...? My Lotus parts manual does not show anything that I think resembles what I'm looking for here... A little help for a "newby" at the Lotus game... where exactly are these "O" rings located? I'll check the O2 and get back to you! Drive topless!! Cameron >> Edited by autocross7 on Thursday 2nd October 01:56

Cameron,

Thank you for the kind words. Must have missed my Ginko-Biloba today, you got me... the EFI cars do not have the rubber 'O' rings or isolators. These are used on the carb'd cars only to isolate the fuel bowls from engine vibration which can foam the fuel. As such, they are soft mounts and not really very tight.

The truth is, I answer many questions daily from Esprit owners, both on and offlist, (as well as three other lists I frequent) and rushed a reply to you without checking my manuals and notes. Mea Culpa for not having done so prior to posting my response to you. The upside is that you have one less thing to check. True, you may still have an air leak at the manifold, but without the rubber isolators, it's much less likely.

So, I would concentrate on the O² (or Lamda) sensor as the most likely cause. This sensor samples the amount of O² present in the exhaust. Any variation from a calibrated amount of O² (Lamda), results in a voltage fluctuation from the sensor which the ECU interprets as a signal to either add or subtract fuel from the A/F mixture. These are especially prone to failure, having to 'live' in the hot exhaust gas environment. Be aware when replacing, there are many alternative O² sensors out there, but as they are calibrated, many will not do an adequate job. Be sure you get one with a 3-wire connector. One wire signals the ECU, while the other two supply power to a heating coil which heats the sensor up to operating temperature on cold start-up. There is a diagnostic procedure for this sensor, but since it's likely to be original, my advise is to simply replace it.

But, first, pull the connector and clean it of any corrosion, replace it and see if that doesn't correct the lean mixture. I would still contemplate the sensor's replacement, but it's status will have moved from 'Critical'.

If that doesn't correct the problem, there are many other components such as the Frequency (or Timing) Valve that could also be the culprit, but these are less likely. However, since this Frequency Valve uses both electrical and vacuum power to operate, be sure all your vacuum lines are connected and not cracked and that all electrical connectors are attached and secure.

If none of this helps, let me know and I'll try to assist further. Somewhere down the list of possibilities, there is even an ignition problem which could trigger the lean condition you describe. Happy Motoring! Jim'85TE

[autocross7]

Well, I have been out of town - forced to drive a rental - AGAIN!!! But... I did get around to ordering the O2 sensor, so I hope to be swapping and posting the results soon...

Drive topless...

[autocross7]

Okay... I know it has been forever, but I just got my baby back on the road with a new clutch, vacume lines, and turbo. I have replaced the O2 sensor after a bit of trouble locating one that would fit...


That bit of poping is still present...

As stated above, the following was check or replaced:

*Vacume lines
*O2 sensor
*Spark plugs look good
*Spark plug wires do not show any indication of
failure and they are really not that old
*Distributor was removed. there was not indication of
a problem as everything looked good. Cleaned it a bit

...Any ideas out there?

I am going to run some injector cleaner through the system to see if that helps...

Drive topless!!!
Cameron

[Dr.Hess]

I am not real sure what you mean by "popping", but backfireing can be caused by an exhaust leak with a rich condition.

Dr.Hess

[nsxlotuspilot]

Hay on ur coolent leak. Try ur hose that comes off of ur water pump to ur manifold. its the hose where ur temp sensor is. The hose seams to get loose on the underside of the intake manifold.I have been there and done that with a 84 and a 97 model. Hope this helps.

[autocross7]

Hey, I found the coolant leak... it got large enough. The water pump weep hole is spilling like a shower head. I'll order a re-build kit for it from JAE... strange thing is (a good thing), I can top off theheader tank and go for a drive. The temp stays right where it should!


Drive topless!!!
Cameron