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1998 New Beetle Misfire

6K views 40 replies 6 participants last post by  Prego 
#1 ·
We have a 1998 beetle with about 130,000 miles. The engine is misfiring all cylinders once the car warms up after 10 minutes or after it rains.
We have replaced the spark plugs, wires and coil, mass flow sensor and a few of the vacuum lines. When watching live data it looks like we lose the feed back from upstream O2 sensor and fuel trim bank 1. Then the check engine light will flash until the 2 sensors appear to come back online. Car still won't drive great but it will stop shuttering. Looking for input as to where to start looking for the trouble spot.
 
#2 ·
If you CEL comes on it will store a code so you can see what it is. But misfires can be cause by a weak fuel pump, clogged fuel filter, improper spark plug gap, bad battery, or low compression. Start with the simple stuff first. Once I had a misfire and when I looked at the wire for #4 it was loose so make sure you have a good connections to each plug.
 
#5 ·
Was the MAF replacement OEM from VW or chinese knockoff? Chinese made ones will work but will make your car run like crap. Looking at the codes I would suggest pulling the spark plugs to check the gap. When you put them back put some dielectric grease on the end to make sure they have a good connection. I would replace the fuel filter since it is cheap and easy to do. Do you have to cycle the key to start the car to build pressure from the fuel pump? You will have to buy a gauge to check that the fuel pressure. Have the battery load tested since our cars are run by computers. It might be a good idea to put fuel injector cleaner in the gas tank to ensure injectors are spraying correctly. It looks like the O2 B1S1 is working just showing its running rich. Should be close to 0%. As for the secondary air injector make sure the lines going in and coming off are not broken, cracked, loose. Make sure it is turning on when you first turn the car on.
 
#7 ·
The MAF was knockoff. But the issue was happening before we replaced it, anytime it rained or after it was driven for 10 minutes or so. The car starts good and the battery was replace a few months ago. We also did replace one of the secondary air injectors lines.In the last year we have replace: plugs, wires, coil, MAF, one of the secondary air injector line, 3 of the vacuum lines, timing belt, water pump and battery. The issue was happening before most of the stuff was replaced. We are also having a transmission issue. Should the fuel trim sensor bank 1 always be slightly changing. When the car is misfiring it goes to 0 and stays there until it stops misfiring. The car smells flooded during this time also. Let me know what you think. Thanks.
 
#6 ·
The MAF was knockoff. But the issue was happening before we replaced it, anytime it rained or after it was driven for 10 minutes or so. The car starts good and the battery was replace a few months ago. We also did replace one of the secondary air injectors lines.In the last year we have replace: plugs, wires, coil, MAF, one of the secondary air injector line, 3 of the vacuum lines, timing belt, water pump and battery. The issue was happening before most of the stuff was replaced. We are also having a transmission issue. Should the fuel trim sensor bank 1 always be slightly changing. When the car is misfiring it goes to 0 and stays there until it stops misfiring. The car smells flooded during this time also. Let me know what you think. Thanks.
 
#8 ·
Yes the O2 S1B1 does fluctuate to be as close to 0 as possible. Check your EGR valve. Make sure it holds a vacuum and isn't all carboned up clogging it. Recheck vacuum lines and make sure no air is coming in. Listen for hisses, spray soapy water look for bubbles, or use carb cleaner. If your car is smells like gas look to see if your injectors are leaking. Gas cleans well and should be easy to spot. Use a long screwdriver and listen to see if your injectors are firing consistently. You might want to put a new fuel pressure regulator on since you have a 99.
 
#10 ·
I would check the wiring to the sensor for corrosion and see if it is getting power. If sensor is bad only replace it with what the car came with. I think it is Bosch. Only other thing would be a compression test to see if your engine is worn out. Bad compression would cause misfires. Minimum pressure should be 110psi.
 
#12 ·
Oxygen sensor and wiring testing: (click arrow for the next pages):

 
#13 ·
Compression testing:


Fuel Pressure testing:

 
#20 ·
You might check your fuel trims (+ or - 10% is considered a normal range); a vacuum leak, will affect this, watch the video, for more info:


 
#24 ·
When I was watching the live data while driving the fuel trim went up to 25 right when the O2 sensor went to 0 and the car started to misfire. It happens about 10 minutes into driving when the vehicle is warm. I am going to do the compression test this weekend. But I am not exactly sure what I am testing on the O2 sensor. After I unplug the black plug. How do I use the scanner the multimeter to test it. Thanks for the help.
 
#21 ·
Not being familiar with the gas models, I would guess that orange line in not oem. If it’s not leaking then check the ends where it connects for leaks. The plastic connections are old and brittle, your leak may be there and not the hose itself. If the plastic connectors are ok find an oem hose and replace that orange aftermarket one.
 
#23 · (Edited)
I'm not familiar with the NB. I have a 2015. But I learned the hard way with none OEM parts. I got great advice from these guys 😁 I'm not sure about your 99, but I now know that I will only put OEM parts on it. Cost more, but if you buy after market, then have to buy OEM. The cost is cheaper, plus the time to replace said part. But she's picky. Good luck 👍 any update on it? O, you said that you replaced the battery. Do you have to tell your car that you did? Or do you not have to on the NB? Just a thought, but these guys can tell you.
 
#25 ·
Did you do the testing procedures; shown in the service manual? Go ahead and print out the pages and follow the tests; this will confirm the wiring, ecu and sensor are good or bad:

 
#28 ·
Did you do the testing procedures; shown in the service manual? Go ahead and print out the pages and follow the tests; this will confirm the wiring, ecu and sensor are good or bad:

So I had a quick question what does.

-
Check resistance for sensor heater at connector to oxygen sensor terminal 1 + 2: Specified value: 1,0...5,0 Ohms(at room temperature).
Is that 1 to 5 Ohms?
 
#26 ·
I test both the O2 sensor. Was slightly out of spec so I replaced it with OEM part. Drove it and no change once it was up to temp about 15 minutes. The fuel trim bank 1 went to the no reading and the car stared to backfire. I did the compression test and all cylinders passed.
Below are the reading when the car started to backfire.

Text Font Screenshot Technology
Text Font Line Screenshot Diagram
Text Font Product Screenshot Website
 
#27 ·
So, when you did the testing of the 02 sensors; did you follow the testing of the wiring and the sensor itself? What were the results of the testing; what was shown to be out of spec? What brand 02 sensors did you buy and install? Bosch, is recommended for the sensors.

If the 02 sensor signal is dropping out; I would be testing the wiring to the ecu, some have had wiring problems, damaged wires/plugs or the ecu, has been seen to get damaged in particularly bad scenarios.

When the car is warmed up and then, the drivability problems, the bank1 sensor1 signal drops out.... does the signal ever come back? When you are driving around; what are the fuel trims at, as noted +or- 10% are within range. Do the backfiring and misfires continue or go away?

The ross tech definitions; are always, a good place to give you ideas on where and what to check.


What were the compression test results; psi for the cylinders?

More work and testing is needed; it can be a challenge to figure things out but you need to do a process of elimination.
 
#29 ·
Seeing, how you had this code in the past; I would also, be checking the catalytic converter, if it is working as it should or it is clogged, etc.


Here is a excellent video; by ETCG, a easy way to confirm, the cat is working the 02 sensors are reading in a normal way as well.



Watch the video and let us know, what the results of the testing is. Thanks.
 
#30 ·
I got a trouble code, for oxygen sensor heater short to ground; I bought a new 02 sensor and tested the new, old one. I did a basic continuity test and the old one, had a broken circuit, the new one had continuity.

In my case, the trouble code; still remained and I could not clear it. That was confusing, so I decided to do a hard reset and then, the code went away, stayed away.

It might help, to pull the plug on the new 02 sensor; then, compare the readings on the old sensor and the new one. The testing for me, confirmed the heater portion was bad; when comparing the new and old 02 sensor.
 
#32 ·
Based upon the service manual:


Check resistance for sensor heater at connector to oxygen sensor terminal 3 + 4. Specified value: 2.5...10.0 Ohms (at room temperature)


So, you seem to be in spec; for the B1S1 02 sensor, I'm assuming, this is the new sensor (what did the old one read)?
 
#33 ·
Another thing to check; is the "readiness" tests, if there is a malfunction in the system, typically the emisssions tests will not "pass" or show a "error" or "fail", indicating a problem. I'm not clear, what scan tool or dongle you are using but with VCDS by Ross Tech, you can "force" the testing and quickly, see the results.


Otherwise, a specific series of driving conditions; must be met, for the testing to be completed (can be done with a test drive but might take multiple drive cycles or days to complete).

Here is a service manual; going over, the readiness test requirement for various VW's and specific engines/models.

 
#34 ·
Once you confirm the cat is working (watch ETCG video; check temps, etc), the 02 sensors are functioning normally and the readiness tests have passed, you can move on to troubleshooting the misfiring. I see, you have replaced allot of parts; attempting to fix the problem, I would be double checking things and I would like a confirmation, on the brand, quality of the parts installed. We have seen aftermarket coils; in particular, cause allot of problems for people, even brand new out of the box.
 
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