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Old 05-14-2005, 05:27 PM   #11
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this is surely a gas problem with that #3 cylinder we have removed that plug a few times and it is always soaked with gas no oil seems to be present, we have also checked all the other plugs several times to see if they are doing the same but they are all burning clean, as I have said before that we have swapped the coil pack and module at a tune of about 160 dollars, we dont know much about what the computers do in these but is there a sensor or such that could be making the one cylinder dump all this gas in there, jst seems so wierd that after you get it going down the road for about 10 minutes then it is fine till u shut it down again then starts all over even with that new injector in the #3 cylinder, we are about to cut this car for scrap but is such a nice car and in really dang good shape for around 250,000 miles, body has very little rust, so all this baby needs is a good bath inside and out and would be like new except that dang engine :( . tyvm for responses and hope to get more as we continue down this road of uncertainty.
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Old 05-14-2005, 07:24 PM   #12
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Pull the fuel rail and switch the #3 injector with a known good injector [one on the fuel rail]. If the problem changes to the cylinder you put the #3 injector on, then the injector needs to be replaced. If the problem stays with the #3 cylinder, chances are the ECU is at fault, and needs replacement.

If you do end out replacing one injector, you may want to just replace them all. It does cost a little more, but will help keep things consistant.


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Old 05-14-2005, 07:35 PM   #13
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I replaced the injector on #3 like I had already said i did with a brand new one and made no difference I have already said this in a previous post. What I am wondering is whatever sensor or computer that controls the injectors is it possibly bad causing that one injector to flow open most the time
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Old 05-14-2005, 08:40 PM   #14
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ok what is the air-fuel injector solenoid we seen that in the manual but doesnt show where it is, and could this trouble be caused bye the mass air flow sensor or the map sensor????
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Old 05-14-2005, 11:27 PM   #15
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Yeah, your ECU is probably shot, or at least it is calling the wrong shots.

A/F Injector solenoid? Never heard of it. The LN3 Engine does not have a MAP Sensor, so it would have to be the MAF Sensor, if anything.

IMO, it sounds like the Injector drivers are bad [within the ECU]. There are no parameters that call for an injector to run 100% of the time. Just not necessary.


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Old 05-14-2005, 11:32 PM   #16
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Each injector is solenoid driven (in the injector) is no seperate one. They are all driven by the ECM and each injector has its own control circuit in the ECM.

At this point I'd probably drag out one of the dual trace O'scopes, hook one to the #3 injector lin and another to the #6 and watch the traces while starting (can do something similar with test lights). Should see a common rattle when you turn the key on and then pulse width modulated (will look like a pulsed square wave) while running.

The problem being only with #3 says it is not the MAF (or any sensor for that matter) because that would affect more than one cyl.

If the #3 is holding something other than ground when off then the ECM may need replacement. Are very common, same computer was used on every "C" 3800, just be sure to use your PROM. If it were here we'd swap one just to see what happened.

Are some other tricks you can try like exchanging injector *leads* (since it is port injection, when you spray is not terribly important, in fact one failure mode is to revert to alternate injection)., the old Rochester FI was a constant flow injection but PWM is more accurate.

These things can get quite frustrating but with the right test tools, you can find what is really happening.

BTW if after a while it runs OK have you checked for a correlation with closed loop operation ? (Need a scan tool to check).
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Old 05-14-2005, 11:38 PM   #17
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I don't think that there is any sensor that has the ability to adjust the fuel flow to each individual cylinder. Lots of sensors give inputs to the ECM, but they are taking readings for the entire engine, and the ECM is making adjustments for the entire engine. So no, I do not think this is a sensor issue.

I wonder what would happen if you unplugged that injector? Would it still leak?

Before replacing the ECM, you might want to try a new plug wire, just to eliminate that possibility, if you've not done so already.

I'm not positive, but I think that these engines have sequential fuel injection (the injectors fire one at a time, as their corresponding intake valve opens). I wonder if somehow there is a problem in the wiring which is resulting in this injector being pulsed twice - once when it should be, and once when another injector is (or should be). But I don't know how that could happen and then go away in a few minutes. Nor am I sure how you would go about testing that theory. I suppose that the ECM could be messed up to the point that it would do the same thing... but again, why would it go away when the car warmed up?

I would def. do a compression test on that cylinder, because that theory makes sense too, and with that many miles you just might be losing some compression.

Have you checked the fuel pressure at the rail? I don't see why it would affect only one cylinder, but at this point you're kinda grasping at straws and you may as well grasp at that one too.

Good luck and keep us posted.
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Old 05-15-2005, 01:05 PM   #18
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The one thing I remember now is that my buddy checked the injectors like someone had said earlier with a scope made for cars that u put to your ears (like doctors cant remember name lol) all the injectors had a clicking sound like was said they should have, that is all except that one that we replaced on the #3 cylinder, we never did check for the click on the old injector because we thought we had her figured out (people always refer to cars as the female sex cuz they are a pain in the a** lol j/k) there should be that clicking sound in all the injectors am I correct even in the new one?? tyvm for responses
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Old 05-15-2005, 09:20 PM   #19
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It'* likely the ECM driver for that injector is toast, but, there could be a problem with the injector harness. The injector gets straight 12 volt power while the car is running and the ECM pulses the ground on and off to change the pulse width or injector "on" time. If the harness has a worn spot to pick up a ground it could cause it to stay on all the time. Try Padgetts suggestion of switching the connectors on two adjacent injectors to verify the problem follows the switch. The injectors should have an audible click when they are operating.
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Old 05-15-2005, 10:35 PM   #20
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it is also mentioned in the Chiltons manual about a high and low pressure injectors, the one we took out looks like the one they show as a high pressure and the replacement looks like a low pressure ( going by the pictures they have in chiltons ) when i called the auto parts store they said there was only one part number besides being a different brand of injector because the one that we put in as the replacement looked just a bit shorter but they said was the right one, and I just looked that up on the advance auto site and lists just one for each manufacturer. I wish i had the access to the car but being in a wheelchair sure limits that so a good friend of mine has been doing the work as we get time to go there(30 miles away for repairs) so we just try to figure out as much as we can by me posting here and ya'll have helped alot and he has been reading the manuals to get ideas, but I am hoping mon or tues we can get back out there and hopefully giterdone. tyvm for all the help ya'll have given and hope this done soon
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