[Cloud9...68]

Soon after a track session last Friday, during which the car ran flawlessly, it developed a rough idle, and when I rev the engine, it sounds like it's misfiring pretty badly - as if it's running on three cylinders, up until about 3500 rpm, after which is smooths out. The problem started on the way home, and was worst during the stop-and-go part of the commute for the first ten minutes or so after leaving work. But then, when I got on the expressway, it abruptly smoothed out, and stayed smooth until I got back into traffic, when it started again.



I did a blink test, and got a code of 1-1-1-3-4, which, according to the documentation, is an intermittent hall sender issue. This isn't surprising, since the hall sender connectors disintegrated years ago, and I've had the whole area wrapped with electrical tape secured with zip ties for about the past five years. So, I'll definitely order a new hall sender. But what concerns me is that I thought a hall sender issue is usually manifested in a loss of power at high rpm, which is the exact opposite of what I'm experiencing, so I was wondering what else I should be checking while I wait for the new sender.



I don't think it's a balance shaft belt issue, because the belt is almost new, and a bad belt wouldn't cause a vibration/misfire to come and go. The engine is extremely smooth - it feels like it wants to rev to 8000 rpm, once I get past the misfires. I also doubt it's a vacuum leak, because it just doesn't feel like one. If feels like there's something electrical that's cutting in and out, and a vacuum leak wouldn't disappear for awhile, then come back. And I doubt it's bad gas, for the same reason. A bad ground also seems unlikely, because I recently removed the engine for a complete rebuild, and carefully inspected and cleaned all ground connections, and of course securely tightened them all when re- installing the engine.



I checked the distributor cap and rotor, and they visually look fine. I ran the engine in the dark last night to look for sparks around the plug wires, and saw no signs of stray sparks, either around the wires, or the coil. I'd love to put a durametric on it, but I don't have one, and neither do I have a windows laptop, so getting a durametric would be a significant investment.



Any other ideas as to things I should check? Oh, and one other question - I noticed that Paragon sells the connector that the Hall Sender plugs into, which as I understand it is the part the usually goes bad. Should I order just the connector, which costs $15, or should I go ahead and order a new sender assembly, which is about $116? I'm leaning toward replacing the whole unit, just because the car is so old, but I was wondering what experiences people have had. Thanks.

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[Bulti]

Just a thought, but maybe it's got something to do with the fuel/air mixture? Like a lambda probe that's starting to go or a bad <acronym title='mass air flow'>MAF</acronym>?

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[Cloud9...68]

I have an air/fuel ratio gauge in the car, with a wide-band O2 sensor, and the mixture seems to be OK. Also, I'm not getting any codes for any other sensors, not that that guarantees that they're OK.

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[flash]

the hall sender generally fails in 2 manners.



1. the heat destroys the connector



2. the magnetic component inside the housing disintegrates



since you already knew it was iffy, and you now have a code, replace the hall sender and see if your problem persists.

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[Cloud9...68]

Agreed. I'm just a little concerned that the symptom I'm having doesn't quite match what I understand happens when a hall sender fails, so I'm afraid it's a red herring. But hopefully not.

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[flash]

the hall sender causes all sorts of running issues. it's not just upper end stuff. for example, when mine failed, the car felt limp, but had no misfires to speak of. i think a lot of it depends on the cam timing.

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[vliegwielolaf1234]

I had that kind of thing with my car half a year ago , misfiring at low rev's above sort off oke to drive ,but lower or slow it wanted to stall



I ended up changing <acronym title='mass air flow'>MAF</acronym> and DME computer and everything works fine since .



So i believe problem started with the <acronym title='mass air flow'>MAF</acronym> , and am not shure why the dme whent bad .



It seemed to be runningin limp mode .



Changed the hall as wel because of age but did not make a difference , in your case i would change it .

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[Cloud9...68]

I think I may have found the problem, but need to confirm. Film at 11:00...

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[Chris Vais]

I was going to suggest moisture around one of the spark plugs.

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[Cloud9...68]

[quote name='Chris Vais' timestamp='1397495706' post='156896']

I was going to suggest moisture around one of the spark plugs.

[/quote]

That's an amazing guess, because that's exactly what I found, and I think I know the source (there wasn't a trace of ethylene glycol in the water). Hopefully this is the root cause. I suspected the hall sender code was a bit of a red herring, because when I ran jiggled the sender's wires while running the engine, it's didn't have any effect on the smoothness of the idle.

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[vliegwielolaf1234]

cheap fix then

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[Cloud9...68]

Yep. If drying everything out and replacing the plugs fixes it, i think I'll still go ahead and replace the hall sender connector, and see if that makes the code go away. I've actually had the code for awhile (which is another reason I dodn't think the hall sender is the cause of the sudden rough low-rpm running), and until the recent problem, the engine hasn't displayed a hint of an issue - it feels like there's about 300 hp under my right foot, and it feels like it wants to rev to 8000 rpm, but my name isn't DS968, so I haven't tried it <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" /> - so my hunch is that the magnetic pick-up is OK. But this is all speculation, or course.

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[Chris Vais]

Cloud, I had experienced the very same thing you described and it was moisture collection down around the one spark plug that was the cause. I had used some water to do some cleaning in the engine bay and knock over a container of water that ran down off the top of the engine.

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[Cloud9...68]

That's good to know - in my case, the water collection was probably a result of the car sitting out in a rain storm with its louvered hood. I think that because there was a significant amount of water in the plug holes of cylinders 2, 3, and 4, which are directly under the louvers, but very little in plug hole #1, which the louvers barely cover.

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[flash]

lol - close up the louvres. they're costing you downforce and cooling anyway

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[Cloud9...68]

Well, that took care of it. That's a relief, because symptoms like I was having can be attributed to dozens of things, and can take eons to troubleshoot. I got off easy.

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[Bulti]

[quote name='flash' timestamp='1397512000' post='156906']lol - close up the louvres. they're costing you downforce and cooling anyway[/quote]



Why is that?

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[flash]

if you take a look at pretty much any car today, the designers are limiting the amount of air that can get under the hood. they block it off anywhere they can, and only allow the air to enter after first passing over a cooling device (radiator, oil cooler, etc). they also block off the underside of the car, and force the air to exit at the rearmost point possible. this promotes the most efficient cooling. it also limits how much air can get under the hood and create lift. our cars were also designed this way, though not quite as much as many modern cars. i've done quite a bit of testing of this, and have created a few items that help (no, i'm not producing them). i've always planned to finish the belly pan, but just haven't had the time to smoke test it.



i'm not suggesting that the louvres are letting more air in, but they may not be letting it out in the right spot.



while there is a possibility of such a thing actually helping with the heat sink nature of the hood, placement would be extremely critical. you would have to see exactly where the high pressure zone above the hood is, and be sure not to interrupt that. it doesn't take much to increase drag. even taping up the gaps between the fenders and hood, and removing windshield wipers can make noticeable changes. having a bunch of air exiting at the wrong point would seriously upset the flow over the car. even the 968 turboRS had a piece added at the base of the windshield to relieve the pile up there. adding more air there would not be good.

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[Bulti]

Interesting! Thanks for the explanation Flash.

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[flash]

no worries. over the years i've played a lot with aerodynamics and cooling systems, due entirely to the fact that none of the cars i was playing with had enough power or cooling (read: british sports cars). as a result, i got to figure out what worked and what didn't, and more importantly how some things that seem like they would work, when misapplied, actually made things worse.



i guess that explains why wind tunnel testing is so expensive.

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