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1989 S4 idles fine but wont rev

 
Old 06-07-2019, 02:35 PM
  #16  
JayPoorJay
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Did you say that you changed the wires as an approach to fixing an existing rev problem? Still, I'll ramble a bit.

I'm not sure (at allll) of the underhood configuration of the S4... But,,, when I changed the plugs in mine I disturbed some things. I later realized that I had shattered the old dried up plug for the TPS at the front of the engine. Disintergrated. The symptoms were exactly the same. Would idle but not respond well to pushing the peddle and would complete bog and stall under any load... Forward or reverse. Making matters worse (I realized even later) I'd also broke off an old dried hose where it connected to metal hose. One that goes from the base of the TB, around the front DS cam cover and over to a shared connection into the intake plenum. Shared a line with the brake booster vac line. All added up to a bad situation.

All I know is symptoms sound the same.
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Old 06-07-2019, 02:49 PM
  #17  
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OP: Post your location. There are RL brothers and sisters stationed all over the place. Anyone with a 1987 or newer car can plug your LH controller into their car and give you an instant result.

Meanwhile... The LH controller sits in a metal frame ("console") next the passenger's feet on the right side. There's a carpeted cover with a snap strap that hides it. You'll likely want to carefully remove the passenger-side junk shelf, unplug the coding plug and ignition protection relay at the right end of the shelf and on the controller console. The console itself has an Allen-head bolt into the right side metal there. With the battery disconnected, remove the big connectors from the controllers, remove the bolt, then slide the whole console towards the rear of the car a few inches, freeing the forward locating pin. Take the whole thing intact to your RL neighbor and they will lay it in the passenger footwell of their car and connect to your LH controller to test.

The LH controller is a known inevitable failure point on '87+ cars. There's a daughter-card inside that was not sealed well when they were built 30+ years ago now, and they fail. There are a couple good service options that include installing a new higher quality circuit there. Rich Andrade near Phoenix (electronikrepair.com) did mine, and it's been perfect ever since. Roger at 928SRUS.com carries controllers rebuilt by John Speake in GB. Other agents include Louis Ott in norther Oregon. Mark and Tom at 928 International have rebuilt controllers too. Any of them will get the job done for you. Maybe the important initial thing to know is that rebuilt controllers have a label on them that tells you it's been done, when, and by whom. The LH controller is the box closest to the cowl, right side looking from the rear of the car towards that console. You may need to take a couple small bolts out to see label. If there isn't a rebuild label on the LH controller, plan on sending yours to be taken care of now.

Popular symptoms of LH failure include injectors that run all the time, such that you can hear them clicking with key on but before cranking the starter. On some the fuel pump fails to run, and on others the symptoms you describe (same failure as I experienced).

Know that you can send your controller and MAF to any of the listed vendors for free testing, and rebuild if needed. If you don't have a nearby test option, this is a pretty easy and safe path to success.

-----

Good luck with your quest, and share your results!
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Old 06-07-2019, 07:56 PM
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Thanks everyone for your responses! I am from southern MN. I just got done cleaning grounds and i removed the MAF and found nothing out of the ordinary. I cleaned the connections and found that the box was still sealed so no one had been screwing with it. I previously skipped changing on coil wire because it seemed nearly impossible but after a little finagling i replaced it and what do ya know it seemed to help a lot! The car is definitely running on all 8 cylinders and now revs somewhat smoothly. My next job is to clean the injectors and if that doesn't solve the problem then i will look into sending my ecu and/or MAF in to be checked out. this is my second 928 and i am very impressed on how clean this car is electrically compared to my Ĺ80. There is hardly any corrosion on anything and just about everything seems to work properly. Might i add that the engine has no oil leaks whatsoever ever. (Am i bragging?) btw i snagged this 928 for $2000. I am making amazing progress on this car and i am so excited for summer
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Old 06-07-2019, 08:08 PM
  #19  
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Here are a few pics of the car. I am planning on power washing the engine bay but i am a little hesitant of doing so.
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Old 06-07-2019, 09:14 PM
  #20  
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Nice project car! Good luck on getting things sorted.
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Old 06-07-2019, 09:34 PM
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Awwwwwsoooome!
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Old 06-07-2019, 10:34 PM
  #22  
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dont power wash the engine you will damage all of the electrics
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Old 06-07-2019, 10:36 PM
  #23  
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Originally Posted by Mrmerlin View Post
dont power wash the engine you will damage all of the electrics
How should i go about cleaning it?
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Old 06-07-2019, 10:39 PM
  #24  
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Good luck with the project, keep us posted.
Very interesting bodywork started.

It may have been better to have posted a picture of that engine bay at the beginning of your thread.....there is a whole lot that you will need to go through on that sucker!
(My barn-find checklist takes weeks, not days.)
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Old 06-07-2019, 11:09 PM
  #25  
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Dont power wash use some wash wipes, like baby wipe but for cleaning the car.

Also that looks like fire damage. Verify your wireharnesses are in good shape before you leave the batter connected. Trust me I had a similar looking engine bay and almost burned down my house being cavalier.

Great project though and it will be rewarding. Good luck
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Old 06-07-2019, 11:39 PM
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These injectors are NOT anywhere near clean. Half were clogged and the rail have bad gas gunk in them. Time for some DEEP CLEANING!!!
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Old 06-11-2019, 11:49 AM
  #27  
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UPDATE!

I cleaned injectors and rail out and now it is running almost 100%!!! I think it still has some bad gas but should come out soon. Idles and revs very good.
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Old 06-11-2019, 02:21 PM
  #28  
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Great news!

From the looks odf the engine bay, there's a bit of deferred maintenance to catch up on. What manyrefer to as an "intake refresh" gets the manifold and cam covers off for refinishing and resealing. The oil vent plumbing underneath gets renewed. There's an idle stabilizer valve that gets replaced, along with knock sensors and the crank position sensors. Do the MAF and the injection controller as soon as practical, because they are ticking strand-you items. They -WILL- fail and they -WILL- strand you.

I've gotten into the habit with our parts vendors to just tell them the project I'm working on and then let them ship a care-package of parts for that. First time I did that was my first timing belt replacement project. 928 International (Jim Bailey at that time) put together a box with everything I know I needed, plus another box of things I would find out I needed. Take full advantage of our parts supplier knowledge and resources, and a lot of frustration will be avoided.

Based on the appearance of the engine bay, you'll be tackling the timing belt project soon, before you risk your valves to a broken or stripped belt. If you have no history on the belt, or it's been more than about 50k miles or five years or so, the belt moves up close to the top of your to-do list before any driving. Belt failure is not cheap, with the damage potentila easily exceeding what you paid for the car. Well bought, by the way.

There are plenty of 928 owners in your part of the country. The 928 Owners Club maintains a support-network list of owners all over the place, folks who are willing to go a little farther to help a fellow owner be you stuck on the road someplace or in your own driveway. worth a look at 928OC.org. GeorgeM here on Rennlist is the membership contact IIRC. Hopefully he'll jump in with more details.
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