1998 E300 will not pass CA smog because of bad glow plug. What to do? - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 01-25-2017, 03:07 PM

My friends E300 is past due on the registration because it won't pass CA smog test. The CEL is on because of one or more bad glow plugs, and the head will have to come off in order to replace them (stripped threads in the head). In the meantime, the car needs to be registered so he can legally drive it. My question is- can a resistor or something else be put in th glow plug circuit to fake out the computer to turn off the CEL? The smog tech will not ignore the light, even though it is only on because of a bad glow plug (or two). Any ideas would be greatly appreciated. Also, he wants me to buy the car from him (I used to own it), as he needs an SUV. Either way, the head has to eventually come off in order to fix the glow plugs. But until then, I would like to be able to get it smogged. Thanks, Rich

Mxfrank · #2 01-25-2017, 03:22 PM

I suppose you could put a glow plug into the circuit. It doesn't have to be installed in the head. Just make sure it's secured so that it's not going to burn anything. Any resistor you install would need to have the same resistance as a real plug, so it's going to get hot anyway.

ROLLGUY · #3 01-25-2017, 03:35 PM

Quote:

Originally Posted by Mxfrank

I suppose you could put a glow plug into the circuit. It doesn't have to be installed in the head. Just make sure it's secured so that it's not going to burn anything. Any resistor you install would need to have the same resistance as a real plug, so it's going to get hot anyway.

I thought about that, but was not sure if it was a safe thing to do, or even if it would work.

tjts1 · #4 01-25-2017, 03:30 PM

A .5 ohm resistor should do it.

ROLLGUY · #5 01-25-2017, 03:38 PM

Quote:

Originally Posted by tjts1

A .5 ohm resistor should do it.

Is there a certain size (wattage or amperage) that would be a minimum? I admit I don't know much about electrical, so I want to get the right thing and don't want to burn down the car.

funola · #6 01-25-2017, 04:38 PM

Quote:

Originally Posted by tjts1

A .5 ohm resistor should do it.

You'll have a hard time finding a 0.5 ohm resistor

that won't blow up.

plug in V & R into Ohms Law Calculator and you'll see what I mean.

engatwork · #7 01-25-2017, 05:13 PM

I've baling wire wired em to the intake manifold.

mach4 · #8 01-25-2017, 05:13 PM

Get a good sized hunk of steel to act as a heat sink and drill/tap holes for the bad glow plug(s). Add new glow plugs to the heat sink and connect the wires from the bad one(s). The computer will never know the difference....the car will start like now (as long as it's not too cold) and you'll get your smog.

...take the next two years to get it sorted out as you desire

you'll have the satisfaction of screwing the CA bureaucrats like they've screwed you for years

Frank Reiner · #9 01-25-2017, 04:36 PM

Roller:

Pay the DMV the $20. Non-Op fee. Then fix it at your leisure.

Do you have a circuit diagram for the glow circuit, and in particular the diagnostic function? If so, the question is: Does the diagnostic circuit look for total resistance in the glow circuit, OR does it look for total current? If the diagnostics look for total resistance the work-around is easy; by pass the actual glow circuit, and substitute the appropriate (quite small) resistance to spoof the test circuit. If the diagnostics are looking for current however, you may have to connect a good dummy glow plug (or two), with the hot ends shielded.

ROLLGUY · #10 01-25-2017, 06:01 PM

Quote:

Originally Posted by Frank Reiner

Roller:

Pay the DMV the $20. Non-Op fee. Then fix it at your leisure.

Do you have a circuit diagram for the glow circuit, and in particular the diagnostic function? If so, the question is: Does the diagnostic circuit look for total resistance in the glow circuit, OR does it look for total current? If the diagnostics look for total resistance the work-around is easy; by pass the actual glow circuit, and substitute the appropriate (quite small) resistance to spoof the test circuit. If the diagnostics are looking for current however, you may have to connect a good dummy glow plug (or two), with the hot ends shielded.

The car is my friend Jim's only transportation, so he can't have it down for the time it takes to pull the head. He will sell the car to me before having to pay to have the work done.

Mxfrank · #11 01-25-2017, 05:52 PM

I=V/R. So a 1/2 ohm resistor would consume 24 amps. P=VI, so 288 watts. That's going to get HOT.

ROLLGUY · #12 01-25-2017, 05:58 PM

Quote:

Originally Posted by Mxfrank

I=V/R. So a 1/2 ohm resistor would consume 24 amps, 300 watts. That's going to get HOT.

I kinda thought it was not as easy as putting a resistor in. I think I will try the dummy GP hack. The only problem is that the intake has to come off. Not a huge job, but worth the effort for what I hope it will accomplish. I might end up buying the car anyway, so the glow plugs will all get replaced eventually.

funola · #13 01-25-2017, 07:30 PM

Quote:

Originally Posted by ROLLGUY

I kinda thought it was not as easy as putting a resistor in. I think I will try the dummy GP hack. The only problem is that the intake has to come off. Not a huge job, but worth the effort for what I hope it will accomplish. I might end up buying the car anyway, so the glow plugs will all get replaced eventually.

Why does the intake have to come off? The "dummy" glow plug can be placed anywhere as long as it's in a safe spot. I'd mount it in a soup can with 2 nuts on the body threads to shield the hot glow plug. The can is ground, electrode to the glow plug lead.

ROLLGUY · #14 01-25-2017, 09:01 PM

Quote:

Originally Posted by funola

Why does the intake have to come off? The "dummy" glow plug can be placed anywhere as long as it's in a safe spot. I'd mount it in a soup can with 2 nuts on the body threads to shield the hot glow plug. The can is ground, electrode to the glow plug lead.

The wires are very short, and can't be removed without removing the manifold. The soup can is a great idea though, I might give that a try.