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loss of power and sputter at 3000 rpm HELP

 
Old 11-26-2012, 03:43 PM
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SuperUser
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Default loss of power and sputter at 3000 rpm HELP

OK, I am at the airport waiting to get on a flight and need some help. On the drive down I had a sudden loss of power and the engine started running very rough.

Some info that may help, I started to do some basic service on the car back at the end of July.
  • Valve job
  • New plugs
  • Air filter
  • Changed primary cap and rotor

The car has been on jack stands for much longer than expected and I did not put fuel stabilizer in:-(. I did have it on a trickle charger. I also added a bottle of Techron before I left for the airport

The car started up with no issues and had driven about 50 miles before the sudden change.

At the airport I only had a second to look it over. It revs quickly but has some backfire on over run.(I have a g-pipe and 200 cell cat). If you hold the RPMs at 2 or 3k it sputters and hunts a bit with a little backfire burble sound. I pulled the coil wire on the primary and the car started up fine.

Thanks for any help, I am really hoping this is not a rebuild.

Last edited by SuperUser; 11-26-2012 at 07:26 PM.
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Old 11-26-2012, 03:59 PM
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Rocket Rob
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You said that you changed the primary cap and rotor. Did you also change the secondary cap & rotor? I'm assuming you did.

Does it idle ok? I'm wondering if you have a vacuum leak in the intake system.
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Old 11-26-2012, 04:13 PM
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I did not change the secondary, ran out of time and had to catch a flight. I do have the secondary and will change it over when I get home.

The loss of power was very sudden and it felt like the car was going to stop running.

The idle now drops lower down to about 400 rpm when I let off the gas after just a second it stabilizes to about 800 rpm.
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Old 11-26-2012, 04:42 PM
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How old (i.e. in years and miles ) are the spark plug wires?
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Old 11-26-2012, 05:10 PM
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I am not 100% sure about the wire age, my car has about 57000 miles on it. It did have the distributer rebuilt but I did not see a line item for the wires.

The old cap I just replaces did show evidence of the wires being pulled, it had some scratches under the plug boots. I do not have the 45000 mile receipt and the dealer has purged the files because they are too old, so it is possible that they where changed then.

Not knowing the age I purchased a set of wires last year but did not install them. I was waiting to do a mist test or get the Christmas tree effect first.

Last edited by SuperUser; 11-26-2012 at 08:11 PM.
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Old 11-26-2012, 06:58 PM
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Misting the wires is an inconclusive test.
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Old 11-26-2012, 07:22 PM
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Originally Posted by darth View Post
Misting the wires is an inconclusive test.
Thanks for the info.

Could it be the DME, whouldn't that effect the idle aslo?

When doing the valve job I removed the o2 sensor to get the tins powder coated, if the connection came loss in the egine bay would it threw a CEL?
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Old 11-26-2012, 07:51 PM
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a bad DME relay can cause a loss of power ~ 4000 RPM
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Old 11-26-2012, 08:07 PM
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Originally Posted by Laker View Post
a bad DME relay can cause a loss of power ~ 4000 RPM
OK, thanks, what about the 2000 to 3000 range?

Luckly I have a spare DME in the car and will give it a try when I get home from my trip.

Last edited by SuperUser; 11-26-2012 at 09:08 PM.
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Old 11-26-2012, 08:55 PM
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Some good suggestions here.

Its easy to accidently dislodge something when changing plugs, caps & rotors. I would suggest making sure the plug wires are properly seated in the new cap, first.

After that, time to check other things:

1) If the plug wires have more than 30K on them, I would replace them ASAP.

2) Replace the DME relay; you should ALWAYS have a spare on board. These are not 100% reliable now.

3) Check head temp sensor connections and wiring.

4) Check Hall sensor connector at distributor.

5) Replace the other cap & rotor when you do the wires and make doubly sure each wire is properly seated in the cap and coil terminal. I see a lot of burned components from DIY'ers.

6) Check the Ignitor connections.

7) Check all vacuum lines; this is a tedious process so patience is required.


There is more to do, but this is a good start.
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Old 11-26-2012, 09:08 PM
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Thanks Guys,

If I got one of the spark plug wires wrong would the car even run and would the idle be stable?
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Old 11-26-2012, 09:28 PM
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When I first got my car 2.5 years ago with 47k on it I ran into a bunch of intermittent faults. It started with a few backfires then the xmas trees and then total sputtering out. It was the plug wires. Steve is correct just replace them. I ended up replacing the coils, coil wires, plugs, plug wires, cap & rotor and also I did replaced the belt on the distributor. I have 65k on it now and have not had a single issue since. Oh yeah I also replaced the DME relay just to be safe too.
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Old 11-26-2012, 09:29 PM
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Originally Posted by SuperUser View Post
Thanks Guys,

If I got one of the spark plug wires wrong would the car even run and would the idle be stable?
I crossed wires after a valve adjustment - #4 and #5 on the top side. The car started and ran, but would pop and backfire on acceleration. It ran because the plugs on the bottom side were still connected and firing at the proper timing. Had me really worried and doubting my ability to to a valve adjustment, though.
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Old 11-27-2012, 02:49 PM
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I will double check the plug wires and install the DME at the airport when I get back.

It has been hard to work today, all I can think about is my poor 964. I am sure I am being paranoid but I cannot stop thinking about the slight ticking my car has always had. The noise is bit louder than my 993 that had the under tray on and hydraulic lifters. I assumed it was valve noise but after checking them and fixing a few it did not quite down. I hope the noise is just normal valve noise, the 964 had good leak down and compression numbers 2500 miles ago in the PPI.
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Old 11-28-2012, 04:15 AM
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Daryl,

"Ticking" noises can be caused by mechanical things such as loose valves, however its also a tell-tale for bad ignition wire connections.

That sound is high-voltage arcing,...
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