Don Terrill’s Speed-Talk

Hi guys,

Long time I've been on this site, but happy it's working again.

I have a question about widebands. I have system with a wideband per cylinder (bosch 4.9) and individual fuel control. Ever since I've had them, almost every winter after starting the car up after it sat for a while, one/a couple of them didn't work anymore.
Advice on when to start up was a bit contradictory. Bosch says on the one hand that you can only start them after the motor is running. At the same time they say that you cannot leave them unheated in an exhaust stream for too long.
Initially I had them all fire up when the ignition was switch to on. Last spring I decided to put a relay in the circuitry and switch them on only after the engine reached more than 400 rpm + after 120 seconds.

So this weekend I fired up the engine after it sat for a couple of months over the winter. All, and I mean all of my widebands do not work anymore...

Not sure what is going on here, but I'm sure they only started after a minute or 2 and then engine reached reasonable temperature ( like 120 °C).

Any ideas, because I'm getting fed up with it and tempted to just go back to one single wideband per bank.

Bosch also tells us the following:

“The sensor must not stay in the exhaust gas stream when it is not heated or when the control unit is switched off.”

Most manufacturer’s of aftermarket wide-band Lambda controllers, pass this point on in their instruction manual in one form or another. It is indeed true that leaving a sensor in the exhaust system without it hooked up to a fully functional controller will kill the sensor. However, doing this for a couple of seconds isn’t a problem. In talking with many of our customers who are the end user’s of aftermarket wide-band controllers, we have often found that many interpret this piece of information to mean that the sensor needs to be fully heated up BEFORE starting the car. In reality nothing could be further from the truth. It isn’t a co-incidence that these customers are the same ones that are killing sensors frequently. After having a brief chat with them and setting them straight their ongoing sensor problems often disappear.

http://www.nzefi.com/bosch-lsu-wide-ban ... lications/

Ok, but even after a couple of seconds the engine still spits out condensate and apparently that is blamed for thermal chock. Bosch warns on the one hand not to switch them on before starting the engine and on the other hand not to leave them in the exhaust unheated. At least contradictory.

I've used it in both combinations and each time it killed a couple of sensors right after a start up after winter time/long standstill. That's about the only thing they have in common.

On my work with marine racing engines in later years when we started using EFI systems and wideband O2 sensors we found out very quickly O2 sensors hate moisture. We had so many fail in marine exhausts we at first went to Speed Density and eliminated the O2's. Later we learned with better O2 locations and protections along with cutting reversion in cam timing we could get some halfway decent O2 operation.

If I am correct your winter environment in Belgium can get pretty moist and cold and wet! Unless your vehicle is stored in a controlled temperature and humidity environment those O2's are going to collect a lot of moisture over a storage period. Remember all the time transportation vehicles are usually driven frequently enough to keep larger amounts of moisture out of the exhaust system and they generally have camshaft timing that does not induce extra reversion like a lot of performance cam timing does.

My suggestion for a simple solution is remove both sensors before storage and put two plugs in the locations. Then in the spring or whenever you bring the vehicle out of storage, fire it up to warm and dry the whole exhaust system, then reinstall the O2's and you should be good to go.

Which wideband controller are you using? I started with an Innovate that was hard on sensors. I've been running an AEM since 2012 with the original sensor.

7 of them are 14point7 and one is an LC2. All of them equally failed.

If the motor has steel tube headers they will spit out rust on first of season (after extended storage) fire up. The rust will foul the O2 sensors.

F-BIRD'88 wrote: ↑Sun Feb 10, 2019 2:27 pm If the motor has steel tube headers they will spit out rust on first of season (after extended storage) fire up. The rust will foul the O2 sensors.

Didn't know that. Anyway to deal with that ? Blow them out with compressed air perhaps ?

What internal header coating would prevent the rusting? Ceramic? Aluminizing?

Once an EFI system is up, running and tuned, is the information one would get from individual cylinder O2 sensors worth the expense and hassle?

jack vines

PackardV8 wrote: ↑Sun Feb 10, 2019 2:47 pm What internal header coating would prevent the rusting? Ceramic? Aluminizing?

Once an EFI system is up, running and tuned, is the information one would get from individual cylinder O2 sensors worth the expense and hassle?

jack vines

Well it does have it's advantages, but if I keep killing them, I'm going back to 2 sensors, one in each pipe.

F-BIRD'88 wrote: ↑Sun Feb 10, 2019 2:27 pm If the motor has steel tube headers they will spit out rust on first of season (after extended storage) fire up. The rust will foul the O2 sensors.

As in the reason factories use stainless.

To be honest I never knew this was a problem.
Anyway I've also seen cast iron exhaust manifolds with O2 sensors.

I would be a mayor pia to have to change the headers. These fit rather good and I performed mods to keep the collectors leak free and so far this has worked.

Moisture kills O2 sensors period! The shield they are equipped with pretty much keeps particle (rust/carbon) contamination off the sensor surface.

I think your problem is moisture.

You mention just two sensors, why are you using more than that?

You need to determine the cause of the failures. Whether electronic or mechanical. Bosch has a lot of troubleshooting help with pictures of O2 sensor failures on their w/s. Can't see from here in the U.S. but it reads like the sensor "circuit" as you didn't post any visible discoloration. That link I provided describes moisture - really the thermal shock from moisture - is a major cause of the failure and it won't tolerate the fast heat rates.

What I'm saying is your need to troubleshoot by the process of elimination. You know they failure after prolonged s/d so condensation is a good possibility. Whether your having some coolant loss only you will know. But you can use the Bosch troubleshooting guide to verify whether color of failed sensor is good or bad and an obvious cause or not.

On the other hand you can over heat the Bosch sensor so have to wonder whether its in a high location on each header pipe getting a direct blast from the cylinder head port?

Your the only one that can eliminate each possible cause of failure. From what I'm reading there are plenty.

I was thinking of moisture myself, but after 2 minutes of running I would think most of it is blow out of the primaries.

They are far enough away from the head not to get damaged. And I would expect the ones that are the closest to fail first.