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Wolfgang, VW Master Technician
Category: VW
Satisfied Customers: 4709
Experience:  Senior VW Master Tech 15 yrs
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Second opinion] Replaced my cam sensor and now the car

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Second opinion] Replaced my cam sensor and now the car doesn't want to run, very rough idle. Acts like it is out if time but we have checked that time and again and it all looks good.
JA: Is the rough idle intermittent or consistent?
Customer: Consistent
JA: What is the model/year of your VW?
Customer: 99 gl
JA: Are you fixing your GL yourself? What have you tried so far?
Customer: Yes, just replaced the sensor then began troubleshooting when it wouldn't run
JA: Anything else you want the mechanic to know before I connect you?
Customer: Also replaced plugs

What was the reason for replacing the cam sensor? Did you scan it for faults, and if so what faults do you have? Do the same faults return?

Customer: replied 1 month ago.
Cranked but wouldn't fire, did a lot of trouble shooting and got the code for the sensor. Now it fires but doesn't run well. Now I have 2, 3 and random misfire codes.
Customer: replied 1 month ago.
Don't recall if it had the misfire codes initially

Thanks for choosing Just Answer . I'm Wolfgang here to help!!

I am confident we can resolve your problem together. Please
understand that I don't know your skill level. In most cases when you have a problem
with the way the vehicle performs, specialized tooling is required to acquire computer
data/information or engine testing results. We didn’t build these complicated vehicles; we
just diagnose and fix them. Also understand that I can't see, smell, hear, or touch the
vehicle either, so it may take a few replies to get to satisfactory results. Note there may be an issue where the complexity of the issue will require a Premium Service. This service will be an addition to the normal question cost. Usually it does not come down to this but keep in mind!! I am also going to direct you with the fastest, easiest and most common things to check first. Please be
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Below is my first answer or request for more information. If you do not understand it, or you need more information from me, or need me to go in more detail.

i do need a vin # to see which gl you have mk3 or mk4 style. second what was the code stored ? i need the Pxxxx # please


Customer: replied 1 month ago.
3VWCC21C4XM426142, p0300, p0302 and p0303
Ok the cam sensor that you replaced was under the cam timing belt gear correct? Did you have a code for that before replacement? Thanks
Customer: replied 1 month ago.
Correct, I don't recall the specific code but it was for the sensor
Did you pull the wires and plugs of 2 and 3 to see if the plugs are wet or black soot?
Customer: replied 1 month ago.
Put all new plugs in, have spark at all 4
Ok if you have spark. Compression test? All 4 cylinders needed to test.
Customer: replied 1 month ago.
Have not yet checked compression. Would that suddenly be a problem after replacing the sensor?
If you got the timing out and bent valves
Customer: replied 1 month ago.
All timing marks are dead on, crank pulley, cam sprocket, flywheel and verified #1 at TDC
To set crank tdi is at trans side. I do not rely on the balancer side due to balancer can slip due to the rubber insulator beteween the 2 pieces.
Customer: replied 1 month ago.
Yep, I have looked over the timing repeatedly and it is all spot on.
If that is the case then I need to know what you have taken apart to do the sensor then after when the misfire came about. I did not take it apart so I depend on u giving this info to see what I remotely can cause this issue you have now
Customer: replied 1 month ago.
For the sensor I pulled the timing belt and cam sprocket and reinstalled everything. At that point the car would start again with the misfire. Replaced plugs, then just troubleshooting other sensors and stuff. Haven't really taken anything else off.
Customer: replied 1 month ago.
I was not driving it when it died so I am not sure if there were any other symptoms when it happened.

have you tried again to see if it will start and run and iff misfiring go to the floor for 5-7 seconds and see if it clears out. let me know!!


Customer: replied 1 month ago.
No luck, could it be the coil being it's a 2 and 3 misfire? Ohms checked out good based off What I found online for it.
Wait a sec you said you have spark on 2 and 3. I want to help but are you saying you did not check spark on 2 and 3?
Customer: replied 1 month ago.
Originally I checked #1 and that was good. I checked again today and the spark on 3 looked stronger than 4 which I found strange being 2 and 3 seem to have the issues. There are several cracks in the coil bit I don't see it arcing at all.
Customer: replied 1 month ago.
I did not check 2 and 3 originally based on what i was seeing, new to this type of coil so i didn't realize how it worked. Had the misfire on 1 also and the plug fixed it so I replaced them all and them 2 and 3 became the regular code.
Being 2 & 3 are harder to get to you may have damaged the wires and may have spiked the coil. May want to check if you have spark on the 2 cyls in question
Customer: replied 1 month ago.
I replaced the coil, it was in bad shape with several cracks and weak spark. It idles better but still wants to die when totally off the gas. Definitely made a difference though.
Did you scan to see if there are any new codes stored ?
Customer: replied 1 month ago.
Same codes as before, p0300, p0302 and p0303
Customer: replied 1 month ago.
If I give it even the slightest amount of throttle it really smooths out, still misfiring but not like before the coil was replaced.

any vacuum leaks that you see check the brake booster line common to crack

Customer: replied 1 month ago.
I will check that. I also tore the line last night for the secondary air pump, the line that feeds it from the intake. I'd assume that would create quite the vacuum leak as well being there is nothing in place anymore to keep that air from going back into the intake. Basically bypassing everything prior to the throttle body is it not?

that goes to the combi injection valve which will not have any affect in vacuum

Customer: replied 1 month ago.
I have new plugs and a coil in, hadn't done wires yet, was gonna order them online being they are cheaper. Anyway after work I decided to check the spark again and #4 is pretty weak. I moved that wire to #1 which has always been strong and the same plug and wire that are weak on 4 look good on 1. What would cause that?
Customer: replied 1 month ago.
ICM go to hell on me?
Do you have an adjustable spark tester?
Customer: replied 1 month ago.
A cheap one yes, tells me the same story pretty much

there is no control module its the ecu controls the coil.

Customer: replied 1 month ago.
When did that change? This was built in late 98. My under standing was it changed in 99

you have an aeg engine and this is newer style !!

Customer: replied 1 month ago.
Could it be an ecu issue and how do i check that

check the wiring from the coil to the ecu to make sure the resistance of the wires are less than 1 ohm .

Customer: replied 1 month ago.
I'll do that tomorrow, it's strange, earlier 4 looked really weak, later on 4 looked good and 1 looked a little weak. Absolutely stumped.

get the wires and then recheck . i think you are going way too deep and its driving you nuts!!

Customer: replied 1 month ago.
It is driving me nuts! Appreciate the help!

my pleasure!!

Customer: replied 1 month ago.
No compression in 2 and 3, 1 and 4 are 150
Customer: replied 1 month ago.
She's toast
I'm sorry to hear that.Anything else.If not please rate my help to you as 5 stars for my assistance. Thanks and my pleasure.Wolfgang
Wolfgang, VW Master Technician
Category: VW
Satisfied Customers: 4709
Experience: Senior VW Master Tech 15 yrs
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