LH module died during driving - repairable?

[Steve119]

Hi guys, went for a drive with my 500 this morning and suddenly the engine would misfire around the steady speed area. On acceleration it was ok-ish, but by the time I got home it ran badly at idle and while revving it. Also right after the start it would nearly die again falling from 1500rpm, before settling at a bad idle...

Started by checking ignition but that was fine on both banks. After reading fault codes that didnt tell much I pulled the MAF connector and voila, it idled and ran ok! Connector back on and the problem was back.
Switched the LH computer with another car and it runs fine...

For testing I put the original LH computer back in and the problem was there .... so defective LH module. Could it be capacitors or are these symptoms something else?

Opened up the module and nothing to see, nothing blown...

 

[Jlaa]

Hi guys, went for a drive with my 500 this morning and suddenly the engine would misfire around the steady speed area. On acceleration it was ok-ish, but by the time I got home it ran badly at idle and while revving it. Also right after the start it would nearly die again falling from 1500rpm, before settling at a bad idle...

Started by checking ignition but that was fine on both banks. After reading fault codes that didnt tell much I pulled the MAF connector and voila, it idled and ran ok! Connector back on and the problem was back.
Switched the LH computer with another car and it runs fine...

For testing I put the original LH computer back in and the problem was there .... so defective LH module. Could it be capacitors or are these symptoms something else?

Opened up the module and nothing to see, nothing blown...

Do you have pictures of the LH module when you opened it up?
Sometimes the look of "bulging Frako capacitors" is somewhat subtle.....

 

[Steve119]

Nothing to see at the capacitors...

 

[ngenius1]

The capacitors can look normal and still be out of spec.
Change them all and it will work just fine after.

 

[kubasz]

I have recently "repaired" one LH for E420 by replacing all those caps. The offenders were those 3 small 22uF capacitors but for the peace of mind i did all of them and the LH cam back to life

 

[gsxr]

Failed caps typically causes a clicking fuel pump relay, which is cured by replacing the caps.

However, the issue described by Steve is very different, and I don't think I've heard of that failure mode reported yet. It would be very interesting to view live data from the bad module and compare to the good one. I'm not confident that new caps will fix it, but I'd sure like to find out the root cause...

 

[maw1124]

Failed caps typically causes a clicking fuel pump relay, which is cured by replacing the caps.

I think this is a bit of an overstatement, empirically. I’d say LH module problems are typically failed caps. I wouldn’t say that failed caps typically cause a clicking fuel pump relay. When mine failed there was no clicking anywhere. So it’s not clear to me that a bad LH shows up anywhere besides poor starting / running that’s not any of the more obvious culprits (NSS, caps, rotors, FPR, fuel pumps).

It’s been somewhat interesting for me to note that most of what goes wrong with these engines are simple “consumerables” which you’d expect to replace every 15 or 30 years. If not those, I think the LH caps are next in line, then the ETA.

maw

EDIT… simplicity is genius here… fuel, air and spark, where air (ETA) and spark (plugs, caps and rotors) are easy… so when you run down the fuel delivery chain (pump, FPR, relay) you very quickly land at the brain (LH).

 

[Steve119]

I've ordered 6 capacitors and will change them out... curious to see if it fixes the LH-module!

 

[Steve119]

My electronics guy askes is the capacitors are normal or low-esr... anyone knows this? thanks!

 

[Steve119]

When checking up close there is 1 big capacitor that has hairline cracks. This isn't ok i suppose?

 

[JCM1]

I had the clicking fuel pump relay (under the rear passenger side seat. My capacitors looked a bit worse than those in post #3 although some of then in the photo look "swollen". Changing out was a bit difficult. I got a de-soldering rig with vacuum from Bangood and made the job much easier. Be sure to use lots of flux!

All the best,


Joe

 

[maw1124]

My electronics guy askes is the capacitors are normal or low-esr... anyone knows this? thanks!

Unfortunately I don't know what ESR means. All I know is my guy replaced Frako with Nichicon capacitors. As I review both companies' websites, I still don't know what ESR means, which leads me to think his question might be irrelevant. If it was my car, I'd get the heaviest duty nichicon that would fit the purpose.

TBH, it probably doesn't matter. I've done enough work with aerospace sensors, chips, capacitors and such to know that the real difference at work here is material sciences over the past 30years. ANY new capacitor that fits is WORLDS better than the 30year old unit that's borne the brunt of the heat and NVH in that engine bay, because... wear, tear and innovation. That said, mine swapped Nichicon for Frako, circa 2012 FWIW.

Hope this helps. Cheers,

maw

 

[BRABUS124]

ESR is a capacitors internal resistence.
This is important to measure as low voltage is used to measure its capacity. But most capacitord fails only when driven to their limits meaning a low voltage test on its capacity will turn out fine nothing wrong. But if you measure the ESR "Equivalent series resistance" this will measure it's ability to obtain its full capacity and reveal if it's failing under load.
So normally you can never see it when their start to fail. But eventually it will fail and often short or letting off the connection. making the power to the module a short or powerless.
One thing for sure. I've changed more than 1000 og these in my time repairing all kind of bokses from cruise controlers to instruments clocks etc. So just change them in what ever module you ever come across. The fluid inside dries out and the capacitor looses it's value and function.