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temporary loss of power

 
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jvandyke  



Joined: 31 Mar 2016
Posts: 205
Location: Hudsonville, MI

PostPosted: Tue Mar 06, 2018 1:14 am    Post subject: temporary loss of power Reply with quote

Hi all. We broke the 924s out of hibernation (briefly) Having done much work this winter and more to come, recent issue:
Start cold, fires right up, idles fine, take off after about 1/4 mile she stumbles, looses all power, drops to idle, you can clutch in, and feather the gas and it sorta responds, after about 30 seconds it clears and off you go, then runs great until it cools down again, repeats.
We have played with coolant bleeding (some serious weirdness going on here).
Suspects:
air in coolant freaking out temp sensor
bleed coolant
DME relay; swapped in another spare, no effect
bleed coolant
smacked DME during event, no effect
bleed coolant
O2 sensor wiring examined
bleed coolant

age old question, fuel or spark, since it's only cold and extremely repeatable i don't think it's something like fuel pump or filter
We drove it 25 miles last Friday and it was fine other than wanting to dump coolant when shut down (erratic coolant levels is another issue)
I run scenarios like "head gasket failure that opens up when just starting to warm up, hydro fouls a cylinder, then clears and heat closes it up and off you go" that kind of thinking costs me lots and lots of time and trouble.
I going to start running sensor checks on the temp sensor, TPS, O2 sensor and so on since I really don't want to make more work for myself. This car is killing me. 2 years and it's time for my kid to enjoy it for a bit.
Compression test may be advisable too.
I want to be systematic and intelligent and diagnose well...for once.
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87 924S project, '83 944 engine,
my son's first car.
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Eric P  



Joined: 21 Jun 2017
Posts: 169
Location: NY, USA

PostPosted: Thu Mar 08, 2018 4:32 am    Post subject: Reply with quote

Take it one step at a time.

Start with the obvious problem, the coolant leak. Where is it leaking? Inside the engine or out?

If outside, take a good look at your water pump. It may be time for a new one. That means new timing and balance shaft belts too (fun stuff right?). Check all your hoses for leaks. A coolant pressure tester can help you find leaks. You can probably rent one at your local auto parts store.

If you think it just hasn't bled right, pull off one of the upper hoses and fill the block with coolant, top off the hose, then stick it back on. Get as much air out as you can before you bleed it.

If you think the coolant is leaking inside the engine, there should be at least one of these signs:
- Coolant in the oil, white foamy look when you drain the oil
- Excessive steam from the exhaust, usually white
- Steam cleaned spark plug and piston crown

Once you have that all sorted, move onto your next problem. Do your basic maintenance.
- fuel filter
- air filter
- new spark plugs
- new plug wires
- new distributor cap and rotor, or at the very least inspect them
- clean your air flow meter (AFM)
- Get your fuel injectors cleaned

Check your fuel pressure if you have access to a fuel pressure tester. It could be that you have something funky going on with fuel pressure. My gut feeling says fuel issues. Any time a car sits, fuel gunks up in injectors, filters, pumps, etc.

Also take a look at your idle air control valve and clean any gunk out of it with carb cleaner then compressed air and wd40. It could be sticking open and giving you issues.

You mentioned the O2 sensor. If you think that it might be the root of your issue, you can unplug it and see if it helps at all. This will essentially put your car in "default mode". If you notice an improvement, replace your O2 sensor.

If you think it's a spark issue, shut the car off during one of its fits and pull the spark plugs to see what they look like. If it's a spark issue, chances are that the plugs will be wet with fuel.
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1980 924 NA, US model
1987 924S, US model
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Eric P  



Joined: 21 Jun 2017
Posts: 169
Location: NY, USA

PostPosted: Thu Mar 15, 2018 1:06 am    Post subject: Reply with quote

Hopefully you already have this sorted out, but I had another quick thought while working on my car this past weekend:

The DME is grounded to the bellhousing next to the negative battery cable lug. I would highly recommend cleaning both the DME ground and the battery cable ground. They're arguably the most important ground connections on the car. A bad ground here could cause all sorts of intermittent issues and banging on the DME wouldn't help. When I took my ground cables off to clean/replace them on Sunday. The cable terminals were very corroded.

If you do this, I highly recommend spraying the ground bolts with penetrating fluid for a few days up to removing the bolts. I snapped the small ground bolt (DME ground) off in my block. Luckily it was fairly easy to relocate to the reference sensor bracket bolt next to it. I don't know what I would have done if I broke the battery ground bolt off. Also make sure to plug the timing hole in the bellhousing so you don't drop anything in there. This would also be an ideal time to replace old corroded battery cables.
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1980 924 NA, US model
1987 924S, US model
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jvandyke  



Joined: 31 Mar 2016
Posts: 205
Location: Hudsonville, MI

PostPosted: Thu Mar 15, 2018 2:54 am    Post subject: Reply with quote

grounds are freshly redone since bellhousing was just off (clutch work), it's still doing it and driving me nuts, I'm going to throw in a new DME temp sensor even though it seemed to pass the resistance test, they're cheap enough, only other weirdness so far is the AFM test is add, DME is sending 5v but on max open flap, only sending back 4v and according to CLark's it should be higher, not sure if that's meaningful, could still be a vacuum leak, I guess only it's so repeatable and regular it "must" be senor/computer related, to my mind
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87 924S project, '83 944 engine,
my son's first car.
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jvandyke  



Joined: 31 Mar 2016
Posts: 205
Location: Hudsonville, MI

PostPosted: Thu Mar 15, 2018 10:58 am    Post subject: Reply with quote

Will swap the temp sensor, if (I'll say "when", because I don't think it's the issue, hopefully my saying that ensures that it is) that proves not helpful will unplug O2 sensor and just keep poking it. At least it's drivable, even enjoyable as long as you let it "clear" itself before you get on the road for serious.
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87 924S project, '83 944 engine,
my son's first car.
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jvandyke  



Joined: 31 Mar 2016
Posts: 205
Location: Hudsonville, MI

PostPosted: Fri Mar 16, 2018 12:34 pm    Post subject: Reply with quote

New sensor in. Same deal, in fact it was worse than ever, got about 300 ft from the shop, headed right back, thought I'd disconnect the O2 sensor while it was acting up, opened the hood, it was running VERY rough, never this bad before, like it was on 2 cylinders, so I wiggled plug wires then grabbed the distributor, as soon as I touched it she smoothed right out, coincidence? Perhaps. I immediately jumped in and joy rode around town, never missed a beat. I'll pull the dist. cap and look, maybe coil wire, the car had a seriously corroded coil wire when we got it (since replaced of course).
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87 924S project, '83 944 engine,
my son's first car.
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jvandyke  



Joined: 31 Mar 2016
Posts: 205
Location: Hudsonville, MI

PostPosted: Sat Mar 17, 2018 8:09 am    Post subject: Reply with quote

Put old O2 sensor back (I'm a pack rat).  Car did not exhibit symptoms.  Looks like it was o2 sensor all along, well, pending further testing.  I timed it, stumble occurred almost exactly at 90 seconds which is when the DME looks at it for info. With "old" sensor back in, no stumble after several minutes of idle.
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87 924S project, '83 944 engine,
my son's first car.
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jvandyke  



Joined: 31 Mar 2016
Posts: 205
Location: Hudsonville, MI

PostPosted: Tue Mar 20, 2018 12:03 pm    Post subject: Reply with quote

power loss, was back on next start up, can idle for 90 seconds, stumble ensures, unplug O2 sensor, clears out, plug back in, goes bad
ran with disconnected sensor for a few days,
confirmed power on two whites (heater wire) with key on run, cut out soldered wires and crimped/shrink wrapped instead, only one test cycle but it DIDN'T do it, will test further tomorrow, it would be crazy if it were soldered joints causing this but why would it "cure" itself when hot?  hmmmm
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87 924S project, '83 944 engine,
my son's first car.
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Eric P  



Joined: 21 Jun 2017
Posts: 169
Location: NY, USA

PostPosted: Wed Mar 21, 2018 4:27 am    Post subject: Reply with quote

It could be that your O2 sensor is taking too long to warm up? Do you have any issues if you start the car with the O2 sensor unplugged leave it unplugged?

It may just be time for a new O2 sensor. Get a genuine Bosch one. They're not that much more expensive. It doesn't have to be for a 944 as long as it has the same number of wires. They're pretty universal. If you get a universal one and solder it into your existing wiring, make sure to stagger your solder joints so nothing shorts out. Even if your O2 sensor is brand new, it could be that you got a bad one. Leaving the plug unhooked will tell you if that's your issue.
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1980 924 NA, US model
1987 924S, US model
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jvandyke  



Joined: 31 Mar 2016
Posts: 205
Location: Hudsonville, MI

PostPosted: Wed Mar 21, 2018 8:34 am    Post subject: Reply with quote

two sensors, same issue, yes we can run without it at all, it's okay, we can plug it back in after everything is hot and no issues, I have 12+ volts on the sensor's heater wires with key on, one is the original sensor (had correct plug) new (that we ran all last year) was universal and the end was swapped over, soldered, then re-soldered, then desoldered and crimped, O2 sensor red herring? maybe it's something different and taking the sensor out of the loop makes the DME correct it, mask it. Of course when warm, all is well so it sure seems like the heating circuit......
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87 924S project, '83 944 engine,
my son's first car.
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jvandyke  



Joined: 31 Mar 2016
Posts: 205
Location: Hudsonville, MI

PostPosted: Tue Mar 27, 2018 11:34 am    Post subject: Reply with quote

took an 8 mile run yesterday, about 2 miles in we pulled over and plugged in the O2 sensor, idle changed a bit, took off, car runs much better with sensor in operation, drove another 4, stopped (to buy more fuses) and left again, ran 6 miles back home (hammered on her a bit, went like stink-which is good)

​​​​​​​
today;
$9 sensor arrived, crimped it in, two runs, no recurrence, will continue to monitor but it sure seems like both old sensor behaved the same way, weird, no? Assume it was just sensor the whole time unless I come back here to whine.
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87 924S project, '83 944 engine,
my son's first car.
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Eric P  



Joined: 21 Jun 2017
Posts: 169
Location: NY, USA

PostPosted: Wed Mar 28, 2018 12:53 am    Post subject: Reply with quote

jvandyke wrote:
today;
$9 sensor arrived, crimped it in, two runs, no recurrence, will continue to monitor but it sure seems like both old sensor behaved the same way, weird, no? Assume it was just sensor the whole time unless I come back here to whine.


I'm glad it worked out! It's a great feeling when these cars run like they should. I've always noticed that the more I drive the better they run. They get grumpy when they sit.

Just a side note: I would definitely solder and heat shrink the wires instead of a crimp connector. O2 sensors can cause issues if the resistance is off. Unless you solder it, any corrosion or loose connections in the connector will cause excess resistance.
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1980 924 NA, US model
1987 924S, US model
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jvandyke  



Joined: 31 Mar 2016
Posts: 205
Location: Hudsonville, MI

PostPosted: Fri Apr 20, 2018 1:35 pm    Post subject: Reply with quote

That's what I thought but WRONG, you NOT supposed to solder them, just crimp. It needs air flow within the wire strands. It's a thing.

PS
car has been running fine
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87 924S project, '83 944 engine,
my son's first car.
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Eric P  



Joined: 21 Jun 2017
Posts: 169
Location: NY, USA

PostPosted: Fri Apr 20, 2018 11:18 pm    Post subject: Reply with quote

I've soldered a few without problems. The wire is stainless and that might be why people say not to? 60/40 nickel solder seems to work well. I hate using crimp connectors anywhere that may see water. After soldering, I use heat shrink tubing that comes with glue to seal everything up.

I've had a lot of bad crimp jobs on project cars. I've never had an issue with solder joints. If it works, it works I guess.
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1980 924 NA, US model
1987 924S, US model
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jvandyke  



Joined: 31 Mar 2016
Posts: 205
Location: Hudsonville, MI

PostPosted: Thu Apr 26, 2018 11:43 am    Post subject: Reply with quote

i also solder and shrink wrap everything, as I did this O2 sensor, and it's replacement and it's replacement but it really is a thing, not supposed to solder, just crimp
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my son's first car.
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