Gurus' assistance needed! '86 Carrera mystery.

[AtomicDog]

All,

I am a new member who has been lurking for about two months now. I recently purchased a 1986 Carrera coupe with 89K mi. I have developed a series of issues that may or may not be related.

1) Wet weather (I thought) caused an intermittent engine misfire/power loss. Upon looking under the decklid, the light show confirmed bad wires. I replaced the plugs (WR7DP), wires (Beru), and distributor cap/rotor (Bosch). Running fuel system/injector cleaner in this tank of fuel, as well

Took the car out last night - ran great. 4k-6.2K RPM is MUCH more dramatic. Pure, blissful, screaming insanity. 25 minutes and no misfire. Driving to work this morning - 15 minutes on the parkway and the no power/power/no power starts up again. It feels like running out of gas, but smoother. What does a DME relay act like when it begins to fail?

2) Heard relay cycling from trunk when defroster was running and noticed the smell of impending electrical disaster. Turned off defroster. Tried to duplicate symptoms the next day, but blower wouldn't run. Replaced relay and checked fuse. Blower will still not run, but fresh air blowers (footwell blowers?) still run well. I should note that the car is equipped with auto-heat, which seems to work well otherwise.

3) Checking oil last night following run - engine almost died, but ran with VERY irregular idle when oil tank cap was removed. I know this represents a vacuum leak, but the car shouldn't stall, right?

4) The car has the typical hunting idle. All the posts indicate that cleaning or replacing the idle air control valve will help correct this. Agree or disagree?

What's going on?

I have a new K&N air filter, and a new fuel filter ready to go in this weekend. The car was driven about 6K miles in the last 8 years until I bought it to use as my daily driver. The car needs a 90K mi tune up when I can get it in. I have Wayne's books, Bruce's book, and the Bentley manual for reference.

[Rot 911]

If it feels like you are running out of gas, you probably are. I would first replace the fuel filter seeing as how you already have a new one.

[imcarthur]

Originally posted by AtomicDog
2) Heard relay cycling from trunk when defroster was running and noticed the smell of impending electrical disaster . . .

It sounds like your main blower fan is toasted. The fresh air blowers - operated by the dash controls - not the between-the-seat controls - is a separate system.

See AutoHeat for an explanation.

Ian

btw welcome to Pelican.

[AtomicDog]

Kurt V,

Thanks for the reply, and the suggestion. I'll be replacing the filter before the weekend.

How could this be an intermittent fuel flow problem? Engine load is very moderate when the phenomenon begins... I had a similar sensation from a '78 VW rabbit with a failing fuel pump relay many years ago.

Thanks,

Chris

[Rot 911]

Chris it could be any number of things, but might as well start with the fuel filter.

[ChrisBennet]

Originally posted by AtomicDog

3) Checking oil last night following run - engine almost died, but ran with VERY irregular idle when oil tank cap was removed. I know this represents a vacuum leak, but the car shouldn't stall, right?

4) The car has the typical hunting idle. All the posts indicate that cleaning or replacing the idle air control valve will help correct this. Agree or disagree?

What's going on?

I have a new K&N air filter, and a new fuel filter ready to go in this weekend. The car was driven about 6K miles in the last 8 years until I bought it to use as my daily driver. The car needs a 90K mi tune up when I can get it in. I have Wayne's books, Bruce's book, and the Bentley manual for reference.

#3 The idle stabilizer valve should compensate for removing the cap as long as the restrictor is present in the breather hose. Someone had a picture but I can't find it at the moment.

#4 The ISV can only control the idle within a certain "window". If the engine "wants" to idle too far outside of that window the ISV will not be able to compensate very well. When it's really bad you'll get a "RrrrumpRuumpRuuump" type idle.

Cleaning the ISV can help but they do eventually wear out.

If you want to look for leaks, I posted some pictures in this post

Hunting down Motronic vacume leaks: What does the thermo-switch do?

The factory paper filter is not a restriction on these motors and filters dirt much better.

When you replace the fuel filter, write the date on it with a Sharpie. Saves you or the next owner from looking through your records to see when it was changed last.

Welcome to the board!
-Chris

[AtomicDog]

Ian and Chris,

Thank you for the tips, the welcome, and the links. More work for this weekend. Two questions come to mind:

Is it a bad idea to use a (non-lit) propane torch to locate vacuum leaks on a 911?

How do you get to the "main" blower? I thought the one in the engine compartment WAS the main blower. Maybe I misunderstood the rennlist animation...

Thanks for the wisdom,

Chris

[imcarthur]

The main 'heater' blower I should have said. It's the black fan on the left that I have circled.



Unplug it from the connector & run 12V directly to it to see if it still works.

Ian

[john walker's workshop]

if the head temp sensor is still the old single wire type, replace it with the updated one with two wires in the plug. they are famous for making the engine die or cut out. replace the DME relay too, if it's an old one. check the date on it.

[Jeff]

AtomicDog, I had the same problem with my 87. It was the Cylinder Head Temp sensor (CHT). It acted, as you stated, like it was running out of gas. Check for cracked wiring and see if it has been updated to the 2 wire type. If not do it.

[greglepore]

Listen to JW, as usual. This was the failure mode for mine, and if its the single wire its needed preventive maintainence anyway. Do the fuel filter, but I'd bet good money its not that. Could be DME relay as well, I'd carry a spare - if you don't carry a spare, buy a new one, replace the existing one, and use the existing one as your spare. Could be any of a number of other things, but those are the usual suspects.

As to blower, sounds like it might be seized, try to run 12v direct to it (brown wire is always ground). If it doesn't run, you can a0 replace fan motor w/ something from Grainger; b) backdate the heat or c) buy the one I have for sale on the used parts board.

[AtomicDog]

Guys,

When I replaced the plug wires, I noticed a pair of wires (one brown, one white) that went through the tin above #3 cylinder. I guessed at the time that this was the going to the head temp sender. I remember thinking that it was a good sign of the later sender.

Any thoughts on the fuel pump or relay? Are these not normally a problem?

Thank you for the advice. I hear and obey (kowtows to gurus).

I believe I'll search for threads on recommended spare items to keep in the car...

Thanks again,

Chris

[greglepore]

The wires going thru the tin could be the wires to the O2 sensor.

The problem could in theory be fuel pump or relay or the wiring to either, but these rarely fail intermittently, whereas the dme relay and the cyl temp sensor are notorious for intermittent failures. Cyl temp sensor in particular for the type of failure mode you describe.

[DW SD]

The DME relay is the fuel pump relay, which makes is another reason it is a cause for intermittent troubles. Your cycling relay is probably not that. The engine will die if the fuel pump dies or shuts off.

I hesitate to mention this since John didn't suggest it, but:

You can do a test on the fuel pump and run it by a jumper and do a volume test (maybe you could do it when the fuel filter is removed). Also, I'm pretty sure there is a test port on the Fuel Injection rails to check pressure, too.

I have the blower motor that I removed from my '86 Carrera engine. You can have it cheap, if you determine yours is burned out.

Email me:
dougwierenga@cox.net

[AtomicDog]

Thanks again to all...

AN UPDATE - which found me stuck on the side of the road...

First, I was wrong about the wires going down through the engine tin. There are three, two white and one black. I believe that greglapore is correct, and that these go to the O2 sensor.

Second - When I had been driving the car home from work for about 15 minutes, it started acting up again. I pulled over, put the car in neutral, and stopped. The idle went up to about 2400 rpm, stayed there for about 10 seconds, dropped to 1500, went back up to 2400 for 10 or so seconds, then dropped to 800, where it stabilized. Over the next few minutes, the car did this twice more, then remained at 800 rpm, idling.

I attempted to drive the car into a nearby parking lot, but every time I eased out on the clutch, the car would drop off with zero power and erratic 800-2400 idle. When the car stalled, it took me almost a full minute to restart the engine. It would crank, but not catch for that time - then started.

I parked and waited (gotta' love the German cars and their coma/recovery) for 45 minutes. Then I started it up and carefully drove home. It repeated the power loss 200 feet from my house, but I finally made it.

WHAT THE *&(!@$*%!!&##!?

Idle air control valve, DME relay, or cylinder temp sender??

Help me, OBI-WAN KENOBIs. YOU'RE MY ONLY HOPE!

Chris

[rcaradimos]

Idle air control valve(clean), DME relay(replace), cylinder temp sender(replace w/ updated two wire)

[gerry100]

Last time a car behaved like that for me, it was a fuel filter.

Fuel flow reduces to a trickle, line gets warm enough and you get vapor lock.

Car stops, line cools off and away you go until it gets warm again.

I'd put the fuel filter in first and see what happens.

You should get a spare DME and do the CHT sensor is it's the old type. I think all of the 3.2s go through this.

[AtomicDog]

All,

Replaced the cht sensor as it turns out that mine was the one-wire style. Those grommets go in (greased with silicone) much easier than they came out.

Replaced DME relay, as well. The date of manufacture was October of 1985. Yeah, I think it was time for a new one.

The aforementioned problem is gone. I thank you all again for your recommendations.

I must confess that I got busy/lazy, and have not changed the fuel filter. I think this may be significant, as my fuel pump is noticeably louder over the last two weeks. Guess what I'm doing this weekend... Yes, and T/S-ing the blower, too.

ChrisBennet, I also found and patched one big vacuum leak. I trust it will hold until I get a chance to look for any others and order parts. You were spot-on about the idle control valve...

Chris

[greglepore]

yeah, I think when the cht fails the mixture goes waaay off, probably rich, thus the stall and then the trouble starting and the erratic idle. Glad it cured it.

[AtomicDog]

Greg,

I'm very glad I have a resource like this BBS. You guys have all the knowledge I don't...

BTW, you were correct in your statement that the wires I saw went to the O2 sensor.

Thanks again,

Chris