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Old 02-02-2012, 10:30 AM   #1
Ninja007
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Default Misfire on 1 cyl, then 2, 3 then dead

Was driving my car home from work 1990 760 Turbo and it developed a misfire on one cylinder during acceleration. I went to run an errand later and it continued to misfire one cylinder, was worse at idle and higher load. After about two miles it started misfiring worse on 1 to 2 cylinders, I was a mile from home so I decided to try to make it home, but the problem got worse, then misfired on 3 cylinders then just quit. I had to push it into a parking lot and get it towed home... So, question is, what causes the car to die a slow death, ie. over the course of a couple miles develop a misfire that gets progressively worse until the car wont run anymore? Im looking for suggestions to help me troubleshoot.

Before this I have done quite a bit of preventative maintenance, all new ignition coil, ignition amplifier, radio suppression relay and fuel relay

After this happened I installed new spark plugs and wires, no change and put gas in the tank (fuel guage doesnt work) just to rule those out.
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Old 02-02-2012, 11:19 AM   #2
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When you crank and it doesn't go is gasoline being injected?

Check grounds for the injectors and the main system relay/suppression relay.
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Old 02-02-2012, 11:34 AM   #3
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You'll have to do some basic tests. If you changed the plugs with no success, I'd suspect fuel starvation, but check for spark as well. Bad fuel filter. Pull the amm connector, see if that helps. Pull the injectors and make sure they are spraying when you crank (DISCONNECT COIL FIRST). Check for bad FPR by pulling the vac hose and making sure no fuel is coming out.
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Old 02-02-2012, 01:05 PM   #4
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Originally Posted by Canuckvolvo View Post
You'll have to do some basic tests. If you changed the plugs with no success, I'd suspect fuel starvation, but check for spark as well. Bad fuel filter. Pull the amm connector, see if that helps. Pull the injectors and make sure they are spraying when you crank (DISCONNECT COIL FIRST). Check for bad FPR by pulling the vac hose and making sure no fuel is coming out.
all for the above testing...I *always* make it point to check COMPRESSION before
I engage in ANY parts testing (unless it is PATENTLY OBVIOUS that "fuel"
is pissing all over the engine bay from a leak or "spark" is crackling off the coil tower
or arcing against the cam cove)r...

"dead" cars get the three minute scan:
1) pull the 710 and verify cam spinning
2) 2 second shot of ether into the intake (if there is spark it'll bang)
3) pull a PLUG END spark wire and ck for a healthy blue spark...

it's a quick and dirty methodology for verifying "air pump operation" /
fuel / and spark troubles...
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Old 02-02-2012, 02:06 PM   #5
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I'm going to bet on a crank position sensor. The symptoms are those of a failing/failed sensor.
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Old 02-02-2012, 03:26 PM   #6
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Good ideas,

Did compression test about 2 weeks ago got about 130 across the board, so I want to rule out spark and fuel before compression.

Replaced fuel filter ~20k ago
Replaced Crank Position Sensor about 15k ago because it went bad. Left me with a no start, but it failed much differently, the car just wouldn't start and there was no jump on the tach.
Unplugged AMM, still no start

I will start by seeing if I get spark out of one of the plugs, then test the FPR vacuum line and then see if I get fuel from the injectors.

Thanks for the tips, I think I finally had the moment where I understand the troubleshooting methodology.

1) spark - test the plugs because they are the end of the system, no spark means part of the system failed, then work back from there.
2) fuel - test the injectors because they are the end of the system etc.
3) compression, no squish no boom
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Old 02-02-2012, 03:36 PM   #7
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Quote:
Originally Posted by saq View Post

Check grounds for the injectors and the main system relay/suppression relay.
A little help on this one, do I check for continuity or a certain resistance or voltage? For example if I was to check the ground for the injectors, where would I put the + and - lead of the ohm-meter and what setting would it be on?
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Old 02-02-2012, 05:34 PM   #8
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hows the cap and rotor?? maybe the diz cap is cracked...
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Old 02-02-2012, 08:19 PM   #9
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Quote:
Originally Posted by Ninja007 View Post
A little help on this one, do I check for continuity or a certain resistance or voltage? For example if I was to check the ground for the injectors, where would I put the + and - lead of the ohm-meter and what setting would it be on?
Before you start going after specifics check the basics.
First check for spark.
The for fuel.
Then compression.

Figure out which is missing and go from there. It could be countless differen things causing the problem.
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Old 02-04-2012, 07:44 PM   #10
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Today I checked a couple of things, started with spark, and took a video, its hard to see but there is spark, it looks a little bit weak/inconsistent, but im not a very good judge of these things

http://youtu.be/Xq5KFNzT3Ts

Then moved to fuel, first checked resistance in injectors - all four have a resistance of 2.6 Ohms.

Then I decided to see if fuel is actually spraying, so I unbolted the fuel rail watched the injectors spray. The spray pattern is more like a stream, got two videos of it, both kind of crappy... I depressurized the fuel system before I took this vid and I think the fuel is just getting back to the injectors, so the spray is messed up on some of them.

http://www.youtube.com/watch?v=yNzhKtlM2Qo

The second vid I had cranked it for a while longer, in real life you can see equal amounts of spray from each injector, and all of their patterns look like a stream.

http://youtu.be/8_8IZvivRM4
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Old 02-04-2012, 07:51 PM   #11
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So if it has spark and has fuel then what's that third thing you need to check?
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Old 02-04-2012, 07:57 PM   #12
Ninja007
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Originally Posted by badvlvo View Post
So if it has spark and has fuel then what's that third thing you need to check?
Lol, I know I need to check compression, i'm just bitter that I did it two weeks ago and now I have to do it again.
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Old 02-04-2012, 08:50 PM   #13
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Yeah, never fun but got to do it.
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Old 02-04-2012, 08:56 PM   #14
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Quote:
Originally Posted by badvlvo View Post
Yeah, never fun but got to do it.
listen CAREFULLY to his video... I'm getting abnormal cranking sounds like
compression is NOT even..as in..."whuda whuda WHUDA whuda.." or
do my ears be messin w/me???


hmmmmm
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Old 02-04-2012, 09:26 PM   #15
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Air.
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Old 02-06-2012, 11:03 PM   #16
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Compression results: 149, 148, 149, 150

I hooked everything back up and it fired after cranking for a couple seconds, ran on 2 or 3 cylinders intermittently and I had to keep the gas down a bit to keep it from dying. I ended up having to mod the new bougicord wires I got because the plug female end was so far into the wire housing that it would bottom out on the cylinder before the plug male found its way into the female. Pissed me off that I had to modify it to fit correctly. I forced them on there and the car ran fine so I let it warm up and idle, and gave it a couple stabs with the gas pedal and it seems to work now. I'm not confident it will stay the way based on the way it was behaving, but we shall see... Times like these make me glad I have AAA and a spare car to drive.

Side note, I checked the spark on Cylinder 1 today and it seemed MUCH stronger than cylinder 4 I checked the other day, if the problem pops up again, i'm gonna check out the cap/rotor

Last edited by Ninja007; 02-06-2012 at 11:11 PM..
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