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s4 sputtering

 
Old 07-12-2010, 09:25 AM
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tylenol
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Default s4 sputtering

Ok I have changed the LH and the MAf had diagnostic work done at the dealer checked for vac leaks you name it. Ran good for about a week and now back to the same problems?? Runs good and then it will spit and sputter fall on its face and take off again never consistent cold hot doesnt matter. Any Thoughts??

Thanks
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Old 07-12-2010, 09:36 AM
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SeanR
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Year of car?
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Old 07-12-2010, 09:45 AM
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tylenol
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sorry 87
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Old 07-12-2010, 09:59 AM
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Mike Frye
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Wow.

Lots of possibilities and not much to go on.

I'm not an S4 guy but I'm thinking the gurus on here will need more so I'll ask for a little more history.
First, how many miles on the car and can you give a little more history on the problem. Is the car new to you? Has it ever run properly for you? If so, when did the problem emerge? Is it driven often or stored for long periods of time? How many miles on the car and how long have you had it?

Do you do your own work or use a shop? You said the MAF and LH were replaced, what led you to decide to do this?

And finally: Was any work done prior to this problem cropping up? Usually the last thing that was done before the problem arose is the first thing you'll want to check.
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Old 07-12-2010, 10:09 AM
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One word

DEALER

There are few if any stealerships with any real knowledge of 928s.

Where did the replacement MAF and LH come from ?

Where are you ( I assume in the US) - There are a number of shall we say "approved by this forum" mechanics/techs/gurus that work on 928s scattered through the US. You may be near one of them. Even better you may be near one or more of the other helpful and well informed amateurs who could just come and spend a saturday afternoon working on your car in return for beer and pizza - I'm not promising but if your in NSW Australia I'll figure it out for you for beer and pizza.

More info required diude
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Old 07-12-2010, 10:21 AM
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tylenol
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ok here goes...the car has 51,000 miles on it. I have owned it for about 4 months. Yes it sat quite a bit before I bought it. was bringing it home after purchase and it just quit (side of the road). Took it to a local shop in minneapolis specializing in porsches not specifecly 928s though. They discovered the lh was bad. Had it shipped home which is Kansas city by the way. Ran good for a couple weeks then started having this sputtering problem and finnaly just quit. Took it to aristocrat motors where they have a porsche mechanic who has worked on almost every 928 that has been in kc. They determined it had a bad maf. Had Louis Ott rebuild the maf put it in and drained all gas put new fuel in and ran good for about 2 weeks now sputtering again. ?? Thanks
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Old 07-12-2010, 10:42 AM
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I know this sounds weird but I had a small gas leak because the hose to the pump was not tight. My '91 $$$$4 stumbled, missed and dropped to 4 cylinders at idle from time to time. Once the hose was tight, it all went away. I dunno, I guess it was a fuel delivery/pressure problem. Sometimes it's the simple s**t.
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Old 07-12-2010, 10:46 AM
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Easiest stuff first - suggest to disconnect the battery and let the LH re-learn the idle. It's totally a long shot, but it's an easy fix and eliminates the possibility that the LH (btw, did you put in a new or rebuilt LH??) is not working right or getting all wound up by bad sensor data.

Since it's pre-'89, there's no ignition-protection circuit, which can cause the sporadic problems you've been having if it is activating when it shouldn't.

Do these symptoms sound familiar to anyone who has had a fuel pump failure, particularly after sitting??

If you get it running again, try a Sea-Foam treatment to the gas (and one in the oil while you're at it) - it will clean out your pipes nicely.

Good luck!
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Old 07-12-2010, 11:08 AM
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Does sputtering mean running on 4 cylinders at times? Are the coils, coil wires or coild connections possibly bad?

Checking other easy stuff like grounds, wiring inside the MAF, Temp2 boots are also possible failure points. The wires there are bent for 20+ years and eventually crack and the insulation crumbles off. Worth a look see. Rog100 has the replacement 2 and 6 wire Bosch/AMP Jr Timer plugs and boots.

Good luck...force be with you and all. Post what you find.
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Old 07-12-2010, 11:13 AM
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Critical S4 grounds are at the back of the valley of the motor, buried under fuel regs.

Coil wires are a good suggestion, too.
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Old 07-12-2010, 11:29 AM
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I vote ignition. Check coil wires, coils, distributors, and rotors. Final stage ignition modules (the thing at the front of the car ont he driver's side with the two plugs going into it) could also have similar effect, but they rarely go bad.
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Old 07-12-2010, 11:30 AM
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Check for fireworks in the engine compartment. Dark room, start the car and watch. The coil wires might be corroded, plug wires might be crappy.

Do this and also search for the location of all the ground points. Start with the basics that are easy to do on your own, then go from there.
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Old 07-12-2010, 12:08 PM
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Presuming fuel, LH and MAF are known good …

Sputtering, but still running makes me think ignition especially if you can get and keep RPMS up . Like they say, check for fire flies… on a dark night, no lights mist the plugs wires with water and look for ‘lightning’. On again off again, could be hard to explain, but can be caused by rain.

If it sputters and dies, makes me think fuel starvation. Especially, if it runs okay or a little rough at idle, but has no power or reduced power or dies when you give it gas. The fuel pump can be overheating and kicking off (will die) or running weak/low on pressure (might idle rough, but gets worse with throttle input). Also, the fuel pump relay can be failing… try swapping it for another ‘53’ such as the horn relay (or jumper it to test out of the equation). On again off again makes me think fuel.

A cheap one of these might help troubleshoot/eliminate fuel pressure issues:
http://www.harborfreight.com/fuel-in...ter-92699.html
http://s287999742.e-shop.info/shop/a...FPG%2520KIT%26
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Old 07-12-2010, 02:47 PM
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What about the ignition modules in the front of the motor?
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Old 07-12-2010, 03:12 PM
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dr bob
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Originally Posted by Mongo View Post
What about the ignition modules in the front of the motor?
I'm not sure I've heard of erratic operation of those; They seem to work until they fail completely, and then it doesn't happen very often.

The OP would do well to trace back through some of Andy's (Mongo) extended exercises with some similar symptoms. IIRC, the final solution included rebuilding the connector plug to the MAF. It may be that the OP's connector was flexed during install of the rebuild, but there are some wires not connecting well. You can get to the plug on the MAF to inspect it with minimal work-- just pull the lower air cleaner housing and lift out the MAF with the connector. The boots break, the wiring gets an oil bath, and the whole section there can get crispy with age and heat. Replacement connectors are availabl from Roger if you don't want to mess with Eagleday or other suppliers. Roger has all the parts, including the housing, boot, and new pins. Do it like you mean it.

You'lll also want to look at the throttle switch contacts with an ohm meter. testing from the plugs on the brains.
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