Are the following all symptoms of ovp relay failure?

Engine cranks but does not start - starts perfectly 5 min later
Poor gear changing - intermittently
Slightly uneven idle
Surging and unexpected acceleration when cruise switched on

Based on my experiences:
Valve guide seals

transmission fluid and filter

resistor-tips on spark plug wires and/or distributor cap and rotor

definitely the CC amp

I encourage other members to confirm, but does not sound like OVP, anyway. Cheers, Andrew Seidel.

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86 560SEC
85 500SEC Lorinser
83 300D Turbo
75 240D

Your engine is warm, you try and start it, but it only cranks... but will randomly start a short while later.... that is a symptom of the OVP. Also, the OVP has been known to cause a rough idle. But you can try a bottle of Chevron's Techron to help clean the fuel system to hopefully smooth out the idle. WHen last were the spark plugs changed? What about the fuel filter?

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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

I concur about the OVP being the source of warm start problems. The first thread I ever posted involved a warm start problem, and replacing the OVP solved it.

The rough idle problem can be caused by a number of things, electrical, vacuum, or fuel system. That will require a bit of top-down stepping through each of the systems to rule out causes, otherwise you end up just "throwing parts" at the problem.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

when you guys state the engine "cranks". Do you mean the engine seems to ignite but immediately dies thereafter?

I have been noticing my warm engine starts to do this recently. If it doesn't die, it hesitates upon ignition and then maintains the start and rev's high and comes back down to normal. Cold starts are no problem at all. I can get around the warm engine start by gently throttling my gas pedal upon startup.

I've changed my wiring harness at 97K on my 95 C220 to take care of other symptoms and hoped it would solve this one.

I have been reading all about the OVP on this forum and just want to make sure my symptoms are classic OVP before conferring with my local mech. Seems like a very easy change and inexpensive.

thanks!

Good article on start problems

http://www.mbca.org/pages/tech/MBCA_Rough_starting.htm

Rough idle and no warm start problems are probably (hopefully) an OVP problem. My 16V had all the classic problems -- intermittent starting/stalling problems (only when warm), finally no start or idle. I did the following (tho' they might not have needed changing, nowhere in my vehicle records were the parts shown as being replaced -- I call it preventive maintenance):

1. New injectors and seals
2. New cap and rotor
3. New Fuel Pump Relay
4. New air temp sensor
5. New OVP fuse (tho' it was not blown)
6. New Idle Speed Valve

Seemed to work fine for about a couple weeks, then the stalling started happening again. Just for kicks, I unplugged the 2-pin connector for the Idle Valve and fired the car back up. It idled like a charm! Went in to look at my CD and found where the 2 wires go:

a) red/yel -- directly to the OVP
b) red/wht -- to CIS-E Control Unit --> red/yel to the OVP

I've got the OVP yanked and am ready to order a new one. Will let you all know the outcome (fingers crossed). I just installed my Bilstein shocks and H&R springs last weekend and the car looks SWEET! I've gotta get this stalling taken care of.

Brian16V

Not sure what the OVP relay does to the engine if you car has HFM engine management system. It could certainly cause some of these symptoms in a KE-Jetronic car, but my HFM car runs fine with the OVP relay removed. OVP failure will always bring on the ABS warning light. If that light's not on, then OVP is OK.

I suggest you check for vacuum leaks before spending any money - this would tie in with the poor shifting.

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Mick J
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)

I checked the 15A Fuse today on my OVP and it looked fine. How hard is it to change the OVP?

If the engine has a rought time starting WHEN WARM, but starts fine when cold, and runs fine onces started, you could be having a fuel pressure leakdown. Likely suspects are a bad injector (can go hand in hand with a rough idle), or a failing accumulator ($65 part).
This is just a hypothetical. On my w126, replacing the accumulator and the injectors at 100k miles did miracles in terms of smoothness. There was nothing wrong with the OVP.

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

you got it - it runs like new once started. only when its warm, does the enigine start get funky. and it happens more not when I immediately start up the engine again after turning it off, but when it has time to sit a bit - maybe 15+ minutes. My idle doesn't seem to be rough - it sits right around 500-700.

could it also be my spark plug wires?

what's the cost of a bad injector...thanks for the help!

A new injector costs you about $30, plus another $5 or $6 for the seat and the seal. The seat you can most likely skip, the seal is a must. However, identifying the injector is a pain, and me being a former airplane owner and a current pilot, I don't like to take risks - i.e. if one went, then others might go too, so I replaced them all. If you do that, you might budget replacing any air hoses that attach to the injectors (I don't know what kind of car you have, I have a 89 560SEL, and it has two hoses at about $12 a piece that fed into the injector holders.) If you DO do all the injectors, replace the holders as well.

The accumulator might be a first try - you can test for it (search oher posts here). If it fails the test, you got your problem, and it's not bad replacing it - it's just as easy as doing a fuel filter (at least on my car).

I DON'T think your problem is in the ignition or any of the other computerized systems - if it works fine but has some trouble starting warm, I'd bet it's a leakdown, and if it's a bit rough I suspect it's an injector causing the roughness and the leakdown.

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

Great information, I really appreciate it. I'll forward it on to the Indep Merc shop I go to. Sounds like the injectors or accumulators shouldn't be to $$$

Can I just live with the warm start problem or is it a harbinger of worse things?

I haven't replaced my charcoal cannister to my recollection - i wonder if that could also be the case? Im just shooting in the dark now.

Don't know what car you have, but my suspicion is it's NOT a harbringer of worse things to come. But I am not a pro at his...

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

I have a 95 C220 at around 97K miles.