84 911 missing at low RPM

Model:
1984 911 Carrera Cab
Symptoms:
Misses at low RPM (Idling). Doesn't seem to at high or during acceleration

Details:
1) Runs normally when first started up and until optimal operating temperature reached.
2) When warm, misses while idling.
3) Recently when to K&N filter and changed spark plugs, didn't notice if it was doing this before then; can't imagine how these are related--definitely not spark plugs: did it before and after with no change.
4) Similar to problem had with 914. Car would run fine until suitably warmed, then miss at HIGH RPMS. This problem turned out to be points gap too small as suggested by Haynes Man. If 911 is missing at Low, it should then be points gap too large, but an 84 doesn't have mechanically gapped points does it? I haven't gotten inside the distributor yet....

I dumped some STP fuel injector cleaner into a full tank of gas into my car, and my rough idle disappeared. Plugs are about 20K old.

------------------
Mark Szabo
1986 911 Targa 3.2

Mark:

Good to see another Hungarian on these pages. Beszelz Magyayarul? Tough to write when we can't use the accent marks !!!

I have a 1983 911SC.

Turned out to be a non-firing #1 injector. As of Friday, mechanic set to replace injector as current was getting to injector but gas was not being delivered. Case and point, if you're having trouble passing an Eclipse, you're running on 5 cylinders or less.

Kurt, glad you got it solved. Just a question, though. If the car was not firing a cylinder, and thus running on only 5 cyls, how was it that it appeared to be running ok at high rpm and during acceleration? I once had a non-firing injector in my SC, and you could really feel the loss of power and the imbalance of the engine at all throttle positions and at all rpm. It was a huge difference in the way the car ran, felt and sounded.

Does your mechanic think that it was somehow sporadically firing? Or was it dead the whole time?

Brian

Actually, you're right. On the day that I posted that, the speculation was, the new injector would fix it...however, the guy hadn't Actually Tested it.
And, it wasn't the problem. He is out of answers....the injector fired, and I guess the problem now looks like a blown valve? I don't know....I'm going to have to take it to a Porsche mechanic. Ah well, I drove it back the 40 miles on a bad cylinder.

Well, if you guys are now suspecting a bent or broken valve, and your mechanic let you take the car back without performing a leakdown or compression test, its time to find a new mechanic.

Were these tests done? If not, you should have one or both done to see if there is a problem with the valves or cylinders. Again, though, this would seem to be a problem that would show throughout the rpm range.

I'm not sure what you mean by "missing" at idle, but if it is just a rough idle, it may be a vacuum leak or the idle control valve.

Good luck, and let us know how it turns out.

Brian

Check the intake blocks and gaskets for a vac leak. These should be checked yearly at major service and the plastic (or whatever it is) blocks can crack or come loose and not show up till hot when things expand. Good luck.

Okay, the latest news.

It's the first cylinder that's missing only, yet its plug, injector, valves, compression etc are apparently OK.
Porsche agents suggest something in the FI, but what?

Took it to lloyd Mosher in upland, ca who has decades of experience with Porsches.
And, still the matter is "questionable." Valves have been adjusted, basically the leak checks, compression, and all have belts, fuel filter been done etc + a complete 15k maintenance.
Isn't injectors, or valves or plugs or any of those. Still, at idle, it misses. At high RPMS not so.
Could be the Gumout I put in the tank, but who knows. Maybe I caked a sensor or two with Gumout residue.
It's a little better after the tuneup and hasn't really missed much since the last tank full of clean gas, but the problem definitely wasn't completely addressed with the above tasks.
If anyone has any idea about whether the injectors are ground singly and so one bad ground could affect just one cylinder, giving it less current than necesssary to inject well etc, let me know...any kind of oddity like that.
Thanks

What about John Roger's suggestion? Carrera's are known for their intake manifolds coming loose at the heads and/or the gasket block failing at that same point. This could possibly cause the affected cyl to run lean and misfire. Have you CAREFULLY checked these?

Brian

Hmm...well that was the last possible item, according to Mosher. He sprayed some starting fluid all over the intake manifold near #1, suggesting that if there was a leak, the idle will immediately rise quickly. After several sprays (like drenching the left engine in fluid), yes the idle did move up slightly...but it was in his opinion the unlikely fault as in the cases when this ceramic piece had wrinkled and leaked, the idle shot up immediately. He said it could be "starting to crack." I guess the matter is, dare I get under and check it out myself...there's a helluva lot of stuff on that side of the engine, and aside from timing, points, converting to carbs and stuff on my 914, I haven't had much experience as a mechanic.

Regardless of the perfection of the seal, if you spray enough of that stuff in the area, even a very tight seal will eventually intake enough of the molcules to ignite, just as if you left the engine under a water hose, some water would get in!
We'll see. When I solve this, I'll let you guys know what it turned out to be(taking it back to Mosher's after the weekend).

Thanks for your advice.

WOW, I hope you find it, as my '85 is doing the same thing. I did the same mods as you as well. I put in a K&N and changed the chip. Let me know!

thank YOu
Nicholas Hromyak
nhromyak@yahoo.com

This may sound simple but have you checked the valve springs? It's posible that the inner spring is broken and causing the miss.

Good Luck,
Lee

Okay...problem is becoming statistically resolved little by little.
I always get gas at the same station near my work, and I had put some cleaners in the gas tank.
Gumout was one. The car had actually stalled a few times after I put it in.

Anyway...I put in a clean tank of gas from a station in upland, no additives, and have been driving around and no missing at all.
I can't be sure now until I go another few tanks without missing, but it could have been that the gumout, which I had used Improperly had some effect on the instruments.(I put the whole bottle in a half tank and didn't fill the tank as instructed).

The Chip and the filters. I went to K&N filter too, just before this started, but I think it's merely coincidental. However, I'd like to know how much of an effect the chip has on your performance?

Well, I am not a big fan of chips, for a variety of reasons. One reason is possible damage to the ECU when you crack it open to put the new chip in. For this reason, some of the more conservative shops that I know will not install chips in customers cars. Check out www.bimmer.org, in the E28 forum, for my detailed discussion (may need to search the archives). A few people there have had bad, costly and time consuming problems caused by chips and/or installation. I also believe, on personal experience, that the hp increase promised by chips tends to be overrated, at least I could not feel the supposed 28 hp that the chip that I once used was supposed to give. I think alot of owners do feel they are getting big increases, but I think a lot of this has to do with owner's perception. For example, lots of people believe they feel a huge increase when they add a K&N, or Slick 50, or Splitfire spark plugs, or a hot air sucking cone filter, or whatever, when a true increase does not exist.

That being said, I would also agree that lots and lots of people have safely used aftermarket chips. I just would not personally crack open my ECU to put an aftermarket chip in. I've done it in the past (admittedly getting caught up in the hype on the BMW Digest), and was not happy with it.

Also not a big fan of the K&N, as it has been proven by Bruce Anderson to have NO performance gain on a 911 Carrera (in fact, there is really no performance gain even if you leave the filter completely off, because the filter is not the bottleneck), and it lets in something like 4 times more particulates than the stock air filter, based on K&N's own numbers. Again, search the E28 board at bimmer.org for some detailed discussion on this. K&N is really more a marketing thing than anything, in my opinion. Most people that I know in my PCA region that have looked carefully into this do not use K&Ns anymore.

I hestitated to address these issues initially because they tend to be a little controversial, but since you asked directly. . . Basically, my philosophy is that Porsches, and the 911 in particular, are the result of a lot of first rate R and D. Before I change out a stock part, I need to be absolutely sure, or very close to it, that the aftermarket part is really an improvement over stock. Not based on advertising hype or unproven "conventional wisdom," but on proven, reliable facts and data.

Brian



[This message has been edited by Brian Kumamoto (edited 12-24-1999).]

Well, that's a wise choice...especially for things like K&N filters. I agree with respect to those items that aren't emission related.
The one reason I suppose I've accepted the idea of mods in CA at least, is because of emission requirements. Porsche brings the car here to meet very specific emission requirements, thus equipping the car differently and with less maybe 5% or 10%less HP than the same car going to Argentina. Some Turbo versions couldn't even make it to the US in the 80s because of emissions requirements. ( And consider the 1.7 914 with carbs having more HP than my 1.8 FI did stock)

You rebuild a tired engine, one that's now on the low end of all acceptable specs and you expect to gain at most, 10% to 20% increase in horsepower. Yet you put a few sparkplugs and a filter on and you're going to get the same increase? It doesn't make sense.
Although I don't have or plan on getting a chip, I did think that maybe the chip ran the engine in a way that maybe wasn't pollution friendly and therefore increased power, or, it was developed 10 years after the car's stock circuitry. If they offered a brand new FI system based upon modern CPU technology (an FI with a Pentium III 500 mhz processor heh), maybe it could do something...but otherwise, it's hard to see exactly what such a chip would do.
Nitrous if you want a little extra kick. But just a little nitrous. You'd want a very small nozzle--if you're getting more than a 10% increase in HP from your engine, you're going to trash it. View the nitrous as a super cheap turbo charger....but use it wisely, sparingly and in small amounts, and the negative effects on your engine will be minimal.
Soon I"m going to slap a bit of nitrous on my 914, which is very, very tired (over 250K miles, never rebuilt but still running okay probably 60Hp rather than 76HP)
Just to see how long she lasts with it. I'll record the effects of small amounts of nitrous and see if there is any true damage; and then rebuild it.

Chip controlled cars really did not come into being on most German cars (like porsche and bmw) until around 1984 or so, when Motronic was developed. By that time, or pretty shortly thereafter, the hp output of California cars and 49 state cars was the same. With the 911, I think even as early as the SC the Cal and 49 state cars had the same hp.

While it was once true that ROW (rest of the world) Porsches had more hp than US spec cars, this has not been true for many, many years, with any given Porsche model having the same hp for all of the markets.

I think the main way that chips get extra hp out of the engine is by advancing the timing. That's why higher octane fuel is almost always required. I don't think the increase is really smog related, everyone that I know that has a chip passes california smog, even with the aftermarket chip.

I don't really have strong feelings one way or another on chips, I just would not personally spend the money for it again, and would not put my ECU at risk, especially on an older car. The ECUs on older cars have been heat and cold cycled, vibrated for year after year, and, in my opinion, generally do no appreciate being pried open and having the boards cracked apart. Companies like ProGrama are doing pretty good business selling rebuilt ECUs for mid-80's cars right now!

Brian

[This message has been edited by Brian Kumamoto (edited 12-25-1999).]

After reading all the replies, it seems like that you have not checked your spark pug wires! Yes spark plug wires can cause missing too, sometimes at high rpm, sometime at low. It also cost the least to check the wires.

Insert six fine gauge wires into the distributor where the spark plug wires plug into. Connect a long electrical wire to ground. Short out each cyclinder sequencially and observe a drop in RMP. The cyclinder that does not respond to the short is the one with bad spark plug wire. Do this at idle and at a higher rpm, about 2000. Sometimes wire works well at low rpm but not at higher rpm, or vice versa.

I had an Audi before and I spend a lot time dealing with missing at about 3000 rpm. After I changed the wires, it worked perfectly. If a wire is broken inside, it still works for a while because spark can jump over the open and evenually over the gap in the spark plug. However, spark can also jump to any close by ground like a holder and results in a miss.

Hope you solve your problem before y2k.

Thanks the plug wires were replaced with others and didn't remedy it.
I'm going to have to take it to Porsche. Could be a vacuum leak now I think. Poor seal around intake manifold or something.

Hi All,
I have a similar intermittent problem with a 1989 911 Carrera.

From starting, the engine feels very 'lumpy' as if it is not firing on all cylinders, lacks power and does not want to rev up. The problem does go away when the engine warms up which takes about 15 minutes. However, the next time the car is used from cold it may run perfectly sweetly as it did before the service. It does not appear to be related to the ambient temperature.

Performing a rpm drop test has narrowed the problem to cylinder #1 (what is it with #1 ?). I too have replaced the HT leads with no effect. I cannot believe that the injector is clogged because surely then the problem would occur all the time (?).

What I want to do now is to check the injector wiring. I have only owned this car for a couple of months and I am not too keen on fiddling with it. The injector lead seems fairly solidly attached to the injector.

Question: Is there a clip of some sort that I need to undo in order to disconnect the injector wire ?

Cheers