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930 misfire

I have owned a 1987 930 cab for 4 years and had alot of fun with it, minimal problems other than the usual oil leaks and .... It developed a misfire under acceleration last year. I have changed the plugs to no avail. I have not found a local shop I am happy with, would I change the plug wires or check fuel pressure or ??

Thanks in advance,
John G

Old 05-14-2012, 02:43 PM
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Ignition coils and wires live a hard life. I'd start there. Checking fuel pressures is always a good idea but I'd say that when they are out of spec, it's more drive ability and starting complaints than mis-fires.
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Last edited by gsxrken; 05-14-2012 at 04:29 PM..
Old 05-14-2012, 04:24 PM
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Got frustrated numerous times also..

1.Changed plugs to cooper ngk or denso. gapped mine 28-32. out of the box.
2.Upgraded to an MSD-6AL
3.Magnecor wires
4.Epoxy-msd-black coil
5.cleaned and changed ignition coil in distributor-.
6.checked every hose and elcetrical connection in engine copartment..chked battery/fuses/wur/etc..etc.. output..using a voltmeter...
clean connections--front/rear-fuses.

Get yourself a comfortable chair while doing this...u will get there, but it takes time..

Recently, I developed problems..Changed plugs and clamped down tighter fittings to both intercooler hoses and air intake canister..ALL GOOD

Also--chk your AFR'S maybe to rich or lean...on cruz...etc..etc..

I do an italian tune-up..MMO-2-3 ounces with 10-11 gallons/gas-93

GL

Walt

Last edited by wjfk32; 05-15-2012 at 04:59 AM..
Old 05-15-2012, 04:57 AM
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I am not into changing parts just for the sake or as a guessing game, maybe the plugs, but after that I am not sure. I do not know of a good way to check plug wires or a coil? Is there a simple test we can utilize without expensive electronic equipment?
Old 05-15-2012, 10:52 AM
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pull out plugs inspect...I had a crack in the insulator..,barely could be seen.

chk coil with a voltmeter--or borrow another coil..

CD-BOX- chk-- test with another.
Old 05-15-2012, 12:12 PM
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Quote:
Originally Posted by 930cabman View Post
I am not into changing parts just for the sake or as a guessing game, maybe the plugs, but after that I am not sure. I do not know of a good way to check plug wires or a coil? Is there a simple test we can utilize without expensive electronic equipment?
Try this: Pull the car into the garage, turn off all the lights to get it pitch black inside (shutter outside windows if necessary), give your eyes a few minutes to adjust, pop the engine lid and fire her up. Look for sparkies along the wires.

Another way that sometimes works is to connect your timing light to each individual wire as close to the plug as possible. If the timing light isn't firing consistently, then there would be a short to ground somewhere before the plug.

And a third way is to just pull one plug wire at a time and see if it affects/or does not affect the idle.

And, do pull the distributor cap off to look for any cracks or carbon tracks that could cause a misfire.
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Old 05-15-2012, 12:13 PM
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Thanks for the responses, the wires and cap/rotor look old so I will start there. It is possible a clogged fuel filter is the culprit.
Old 05-15-2012, 04:44 PM
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FWIW, there is a big difference between misfiring and hesitation... Misfiring is normally an ignition issue, hesitation is more fuel related; however, there is always the exception.
Old 05-16-2012, 09:47 AM
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more info?

Please desbribe the feeling or sound of the misfire. Is it a single "dut dut dut" stuttering sound as if maybe one cylinder is misfiring? Or is it more of a general "break-up" in acceleration under a load that gets worse with more RPM/boost?

If the plug wires are original, they are likely shielded in stainless mesh covering. Making sparks somewhat hard to see, they also have a resisotor in each connector both at the cap and the spark plug. The ohm spec is given on the outside of the connectors. Typically 1,000 (1K ohm) on the cap side and 3-5K on the spark plug connector. You can check these with an volt/ohm meter I usually start from inside the cap and measure from the innner distributor cap contact, to the point at which it contacts the plug. If you discover high resistance or an open circuit on any one wire, you can then disassemble the wire by unscrewing each connector and checking the components individually per spec. The wire is solid copper core originally, so there should be little to no resistance when testing a bare wire with connectors removed.

The above scenario would relate best to a constant single cylinder misfire regarless of load.

I would certainly inspect all the plugs and look for any variance if this is the case.

If you have a more general "break up" under load...you may have a boost leak which will cause the engine to run very rich due to the nature of the air metering system. Intercooler orings are most common but of host of other items can contribute. This scenario would likely be accompained by black smoke...

The only downside to tossing fresh secondary ignition components at it (other than $$) is the concerns over quality control from more recently made parts, even from respectable manufactuers...cost cutting is hitting everyone, I would personally rather have a good used 20 year old ditributor cap with low miles than a brand new one built within the last few years...Unfortunately, though, without intense testing on an scope, it is really hard to nail down ignition problems on these critters, leaving one little choice than tossing parts at it if fixing yourself.

Then there are the CIS issues but I gotta get back to work

there is my $.02 for the moment, better get back to it, this SC won't fix itself no mater how nice I keep talking to it...

Good luck, I'll check back and chime in hopefully...
Old 05-16-2012, 10:27 AM
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Also, no, a clogged fuel filter is likely not the cause, although I would change it frequently, particularly with modern fuels..

Keep us posted,

Mike
Old 05-16-2012, 02:35 PM
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The misfire does seem ignition related, that is why I started with the plugs. I purchased the 930 in 2009 and have been running it with basically no issues, so it seemed logical to at least new plugs were in order.

The misfire is under load (boost condition) and it feels as a bad plug would. For this reason it would seem the wires, cap and rotor are next. I suppose $200.00 is not too much for a roll of the dice. I could find a shop and let them guess I suppose.

thanks again,
John G
Old 05-16-2012, 05:23 PM
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Quote:
Originally Posted by 930cabman View Post
The misfire does seem ignition related, that is why I started with the plugs. I purchased the 930 in 2009 and have been running it with basically no issues, so it seemed logical to at least new plugs were in order.

The misfire is under load (boost condition) and it feels as a bad plug would. For this reason it would seem the wires, cap and rotor are next. I suppose $200.00 is not too much for a roll of the dice. I could find a shop and let them guess I suppose.

thanks again,
John G
Miguel and Mike both tossed out the possibility of something other than ignition related issues. Since you're seeing this under load (and particularly under boost), it could be as simple as a blown o'ring on the intercooler. That will cause you to run pig-rich when under boost....you'll have a dramatic lack of power and a hard time taching out the engine. Stutter stutt stutt, run like crap when any boost is built. When's the last time you had your IC off and checked the o'rings and such? Maybe put that possibility to bed before replacing ignition stuff.

One more question: How's your idle? Smooth, or otherwise? An intake leak in CIS turbo cars would cause lean conditions at idle, and rich under boost.
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Old 05-16-2012, 06:13 PM
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I had a similar experience when the car would hesitate, but at about 4,000 rpm's. Thought it may be a boost leak, but all seal were good. It turned out to be a bad rear fuel pump. I had it up on the lift while running and tapped the rear pump with a hammer and the pump came to life, but it was still intermittent.

After rear pump replacement I never again experienced the hesitation.

Just my experience.
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Old 05-17-2012, 06:03 AM
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Quote:
Originally Posted by Blaine Sellie View Post
...a bad rear fuel pump...and tapped the rear pump with a hammer and the pump came to life, but it was still intermittent.
Reminds me of my early days with my old MG. Points-operated fuel pump needed a solid rap once in awhile with a tire iron (or hammer, or rock, or whatever was handy). Absolute POS design.
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Old 05-17-2012, 06:58 AM
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The idle is just as it should be, smooth and about 900 rpm. I have removed the and the O rings look fine. It is still lookin like plug wires and cap/rotor. I would feel better if there was a conclusive test for these elements.
Old 05-17-2012, 02:25 PM
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Maybe "misfire" is the incorrect term. The issue occurs when under boost, about .4 atm. I will be rolling along just fine, increase the throttle opening to a point where the turbo kicks in, she pushes ok until it reaches about .4 or .5 atm boost. If I keep my foot into it a rather strong hesitation occurs usually accompanied with a backfire in the intake system.
Given these results I am no longer thinking about the plug wires/plugs.
Is the issue somewhere in the wastgate?
I am currently at a loss. She runs just great until I decide to give her a kick.
Old 05-21-2012, 03:09 AM
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My guess would be fuel pressures or (excessive) enrichment under boost. Best to get a cis fuel pressure tester or get your wrench to check your pressures. Unfortunately without an adjustable wur you can't do to much to adjust it.
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Old 05-21-2012, 05:12 AM
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Agree with Helmsy to check fuel pressure. Follow the standard "tune-up" procedures:

Verify CIS system and control pressures are within spec
Inspect distributor cap and rotor, replace if suspect
Inspect spark plugs and wires, replace if suspect
verfiy ignition timing is within spec
verify operation of advance/retard mechanisms as equipped

tools needed:
CIS fuel pressure gauges (best price from JC Whitney ~$60 IIRC)
Timing Light ~$35 from your FLAPS
MityVac to pull vacuum or apply pressure to vacuum pod on distributor and to vac/boost port(s) on CIS Warm-up regulator ~$30 from your FLAPS

Every 930 DIY wrench should have these items in his/her toolbox
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Old 05-21-2012, 06:51 AM
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Quote:
Originally Posted by 930cabman View Post
Maybe "misfire" is the incorrect term. The issue occurs when under boost, about .4 atm. I will be rolling along just fine, increase the throttle opening to a point where the turbo kicks in, she pushes ok until it reaches about .4 or .5 atm boost. If I keep my foot into it a rather strong hesitation occurs usually accompanied with a backfire in the intake system.
Given these results I am no longer thinking about the plug wires/plugs.
Is the issue somewhere in the wastgate?
I am currently at a loss. She runs just great until I decide to give her a kick.
It is going lean. If an engine is rich it just does not make as much power and makes black smoke.
When the boost comes on he is getting more air and not the fuel to burn with it and it back fires through the intake, classic lean misfire. There must be something on these cars to enriching the mixture to compensate for boost pressure, I would look into that.
Lean is dangerous and needs to be addressed ASAP.
Rich is not nearly as dangerous and more annoying usually.
It is not a waste gate because that would just affect boost pressure and not fuel mixture. Loss of power or to much.
If it was bad wires he would just have dead cylinders under load and not the back fire.
Of course I could be entirely wrong, just my two cents.
Old 05-21-2012, 07:40 AM
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Originally Posted by ficke View Post
It is going lean. If an engine is rich it just does not make as much power and makes black smoke.
When the boost comes on he is getting more air and not the fuel to burn with it and it back fires through the intake, classic lean misfire. There must be something on these cars to enriching the mixture to compensate for boost pressure, I would look into that.
Lean is dangerous and needs to be addressed ASAP.
Rich is not nearly as dangerous and more annoying usually.
It is not a waste gate because that would just affect boost pressure and not fuel mixture. Loss of power or to much.
If it was bad wires he would just have dead cylinders under load and not the back fire.
Of course I could be entirely wrong, just my two cents.
All good input, so many possibilities. A person just has to methodically eliminate things.
I too would check system and control pressures as a starting point. Let's make sure she's not fuel starving (or alternately, drowning). Mr. Ficke, yes there is something on these cars that compensates for boost pressure...it's the warm-up regulator that will lower the control pressure and in a roundabout way allow more fuel to flow to the injectors. Very easy to test WUR operation with the proper gauge setup and a MityVac as already mentioned.

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Old 05-21-2012, 08:44 AM
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