Bizzare 4 cylinder running condition, suggestions?
07-19-2006, 03:57 PM
#35
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Thread Starter
Bill wrote:
Yes.
I don't have access to one nearby, maybe its time for a PacNW group buy. 
pmotts wrote:
Not quite like that. The car ran rough from initial start up. After dinking around with it for about 5 minutes rough running, it smoothed out for the next 5 minutes, but then started backfiring again. I then shut it down because the T-belt light went on.
This car has had some very strange failures in the rebuild process. When I first got her together, there was a leak in the fuel return line where the hard line clamps into the soft line. Once that leak was fixed, 5 out of 8 injectors leaked, FROM THEIR CENTER SEAMS. I've never seen this happen. Basically where the plastic top half meets the bottom aluminum half. I swapped out all of the injectors for an extra used set that I had lying around, maybe I should try switching injectors from port to port. I noticed some ooze on one of the injectors I removed, and just assumed that it was dielectric(sp) grease, but another 928'er confirmed that it was sealant of some kind. We then looked into the injector connectors and the four inboard connectors were caked with the stuff. The clips were cleaned out, and Thurston took a meter to all the injector clips, and after bypassing the limp mode relay, they all read the same. We thought we had the problem licked but on start up it was the same situation.
Crazy stuff. There are so many potential reasons, but none of the potential solutions have worked. I'm reminded of the time when I was in Junior High one my friend's YZ125 stopped running. One of my other friends that was an excellent wrench (for a 14 year old) tore the whole thing apart, put in a new ring, cleaned the reed valves, just did everything, and the thing wouldn't fire up. My other friend and I went over to check on the progress on the bike. This friend was the consumate bench racing B-S'r. He walks over to the bike, pulls the plug, lights his cigarette, then put the bic to the plug electrodes, screws it back in, pops on the cap, straddles the bike. ZINGGGG!!!! It fired up first kick.
I get the feeling I'm missing something really basic here.
Patdon me if you did this already ---If you pull the spark plugs on the non-working cylinders, attach them to the leads and short them against the heads, try to start the engine, do you see good spark?
You can use a "Spanner" or Hammer to do just that - this is the way the Tony found a connector problem on one or two of his injectors.
pmotts wrote:
You say it ran fine for 5 minutes? So it revved good and idled smooth and then suddenly went to an obsessed 4cyl mode?
This car has had some very strange failures in the rebuild process. When I first got her together, there was a leak in the fuel return line where the hard line clamps into the soft line. Once that leak was fixed, 5 out of 8 injectors leaked, FROM THEIR CENTER SEAMS. I've never seen this happen. Basically where the plastic top half meets the bottom aluminum half. I swapped out all of the injectors for an extra used set that I had lying around, maybe I should try switching injectors from port to port. I noticed some ooze on one of the injectors I removed, and just assumed that it was dielectric(sp) grease, but another 928'er confirmed that it was sealant of some kind. We then looked into the injector connectors and the four inboard connectors were caked with the stuff. The clips were cleaned out, and Thurston took a meter to all the injector clips, and after bypassing the limp mode relay, they all read the same. We thought we had the problem licked but on start up it was the same situation.
Crazy stuff. There are so many potential reasons, but none of the potential solutions have worked. I'm reminded of the time when I was in Junior High one my friend's YZ125 stopped running. One of my other friends that was an excellent wrench (for a 14 year old) tore the whole thing apart, put in a new ring, cleaned the reed valves, just did everything, and the thing wouldn't fire up. My other friend and I went over to check on the progress on the bike. This friend was the consumate bench racing B-S'r. He walks over to the bike, pulls the plug, lights his cigarette, then put the bic to the plug electrodes, screws it back in, pops on the cap, straddles the bike. ZINGGGG!!!! It fired up first kick.
I get the feeling I'm missing something really basic here.
07-19-2006, 04:00 PM
#36
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Thread Starter
Are the affected cylinders all fed by the same side of the intake manifold?
07-19-2006, 04:01 PM
#37
Burning Brakes
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That would be my next step.
This car has had some very strange failures in the rebuild process. When I first got her together, there was a leak in the fuel return line where the hard line clamps into the soft line. Once that leak was fixed, 5 out of 8 injectors leaked, FROM THEIR CENTER SEAMS. I've never seen this happen. Basically where the plastic top half meets the bottom aluminum half. I swapped out all of the injectors for an extra used set that I had lying around, maybe I should try switching injectors from port to port. I noticed some ooze on one of the injectors I removed, and just assumed that it was dielectric(sp) grease, but another 928'er confirmed that it was sealant of some kind. We then looked into the injector connectors and the four inboard connectors were caked with the stuff. The clips were cleaned out, and Thurston took a meter to all the injector clips, and after bypassing the limp mode relay, they all read the same. We thought we had the problem licked but on start up it was the same situation.
.
Originally Posted by atb
This car has had some very strange failures in the rebuild process. When I first got her together, there was a leak in the fuel return line where the hard line clamps into the soft line. Once that leak was fixed, 5 out of 8 injectors leaked, FROM THEIR CENTER SEAMS. I've never seen this happen. Basically where the plastic top half meets the bottom aluminum half. I swapped out all of the injectors for an extra used set that I had lying around, maybe I should try switching injectors from port to port. I noticed some ooze on one of the injectors I removed, and just assumed that it was dielectric(sp) grease, but another 928'er confirmed that it was sealant of some kind. We then looked into the injector connectors and the four inboard connectors were caked with the stuff. The clips were cleaned out, and Thurston took a meter to all the injector clips, and after bypassing the limp mode relay, they all read the same. We thought we had the problem licked but on start up it was the same situation.
.
07-19-2006, 04:04 PM
#38
Three Wheelin'
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well, couple things come to mind. If you have air and spark and bent valves you have no running, but you said you checked compression.
so next would be what i saw on the 2nd page. The OTHER time something like this happened to me, the injetor plug wasn't FULLY on the injector clip. Make sure they are fully connected all of the way. Even take the metal retainer clip off to make sure that is not blcokinga nything.
last thing to come to mind is timing, as John S said if you have fuel and spark but they arent hiting at the right time it wont work. however if you use carb cleaner or starting fluid it takes out the whole 'fuel' issue, just spray it down your intake
so next would be what i saw on the 2nd page. The OTHER time something like this happened to me, the injetor plug wasn't FULLY on the injector clip. Make sure they are fully connected all of the way. Even take the metal retainer clip off to make sure that is not blcokinga nything.
last thing to come to mind is timing, as John S said if you have fuel and spark but they arent hiting at the right time it wont work. however if you use carb cleaner or starting fluid it takes out the whole 'fuel' issue, just spray it down your intake
07-19-2006, 04:08 PM
#39
Under the Lift
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Yep, the injectors are suspect. Swapping hole to hole would be instructive. My starter fluid squirt suggestion would be a simple way to verify it is fuel-related.
Per chance it is LH or harness related, a noid light to check whether the injector leads on the bad holes are getting a firing signal would be good too.
Per chance it is LH or harness related, a noid light to check whether the injector leads on the bad holes are getting a firing signal would be good too.
07-19-2006, 04:10 PM
#40
Originally Posted by atb
Originally Posted by Larry928GTS
Are the affected cylinders all fed by the same side of the intake manifold?
07-19-2006, 04:10 PM
#41
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Thread Starter
Andrew wrote:
The battery has been unplugged and plugged a few times. But the engine hasn't been under any load, I wonder if that would make a difference.
Have you tried a bettery reset?
07-19-2006, 05:20 PM
#43
Rennlist Member
FWIW,
Have you used a stethescope (sp) to listen to each of the 4 inboard injectors to hear if they are actually firing? If not, if you have spare injectors try pulling all four connectors on the inboards, plug into spare injectors, and see if they are firing.
Have you used a stethescope (sp) to listen to each of the 4 inboard injectors to hear if they are actually firing? If not, if you have spare injectors try pulling all four connectors on the inboards, plug into spare injectors, and see if they are firing.
Last edited by neilh; 07-19-2006 at 09:36 PM.
07-19-2006, 07:50 PM
#44
Road Warrior
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Originally Posted by Larry928GTS
If so, are you missing any shop rags?
07-20-2006, 01:57 AM
#45
Rennlist Member
...just a thought, but have you checked the ignition modules? I had one fail, and the symptoms sound the same as your problem.