Engine bogs at low RPM when throttle pushed

[thulsadoom]

Hi all, I'm going to post this in case someone else has experienced it and discovered a solution. Neither of my guys have.

Issue: after car is working fine up to temp it will bog horrendously for a while. Continued running it goes away.

- Idle becomes very rough, enough to have me put in idle at stop
- Pressing gas sounds like 4 cylinders engaged and moves but slowly. More throttle does not give more power
- above 2500 to 3000 rpm sound returns to normal, but harder throttle it can bog
- manual shifting to keep RPM up helps just to move in traffic
- goes away after 15 minutes running, especially on highway but that's at higher rpm anyhow
- engine light on not sure of code no other lights
- does not happen every time
- otherwise very well cared for and reliable. Known steering pump leak but level kept up easily
- 180k 1992

Thanks for any help you can provide!

 

[r44raven]

Sounds like the dreaded distributor cap/insulator dampness/contamination has struck again!

Lots of threads here on the issue. You just need to do a bit of trawling, and you'll find you're not alone!

 

[nocfn]

Try getting the car up to temp and actually driving it for 10-15 miles each way at a minimum every time you use it if possible. It may not be getting hot enough for long enough time to fix the phenomenon suggested above.

 

[gsxr]

Sounds like the dreaded distributor cap/insulator dampness/contamination has struck again!

Lots of threads here on the issue. You just need to do a bit of trawling, and you'll find you're not alone!

+1... classic symptoms. Keep in mind the issue is typically the insulators, not the caps themselves...

 

[Boxersix]

Hey that sound kind of like my problem too! My car usually drives great but if I let it sit for two days or longer it will start OK but the throttle response sucks and it sound like it is running on something less than 8 cylinders. Prodding the throttle will get the rev up but it takes about 20 minutes for it to respond correctly and then if I drive it everyday it is fine. only acts up if it gets to sit for a couple days. I was thinking it was my Electronic throttle Actuator letting me know it was near toast. I'll read up on the dreaded distributor cap/insulator dampness/contamination!

Thanks
Boxersix

 

[thulsadoom]

Thanks for ideas. I had the insulator issue before but did not manifest in this way. However, one cap was tightened a bit much and there's a slight crack around the bolt. Also see a few minor cracks in wires so looks like the whole set up needs replacing anyhow.

 

[thulsadoom]

I'll post these for posterity. Not sure that cap crack is that important but interesting to see.. could be combo with the silly hotness of these engines. How often do the wires need to be changed.. oy.

 

[gsxr]

That crack in the outer cap near the bolt won't affect ignition performance. Also, the OE ignition wires typically last a very, very long time. 200kmi+ / 25+ years is not uncommon. The wires often get replaced by shops looking to make money, not because the old wires were bad. (Yes, there have been some documented cases of faulty wires with voltage leaking and shorting to ground, with visible arcing at night, but this is super rare IMO.)

Anyway - the wires in your photo are the aftermarket Bosch gray wires, which have very fragile insulation. The outer gray cover tears easily, but the primary insulation underneath should still be OK. I wouldn't bother replacing the wires just because of the one tear shown in the photo, unless there is visible arcing, or other problems with the wire set. And, I wouldn't buy the gray Bosch wires again.

 

[JC220]

My favourite way to test ignition system arcing is simply to observe the engine running in complete darkness. Any arcing will be seen as blue flashes. Very effective. Just be careful not to touch the HT leads with the motor running- look but dont touch!

 

[thulsadoom]

Thanks for advice. I was thinking the wires actually looked perhaps okay. So culprit is probably just the dust caps inside, I'll start there. I noticed that pelican lists all the Mercedes factory brand ignition items pretty much as not available.. what's best option now?

 

[195910]

That crack in the outer cap near the bolt won't affect ignition performance. Also, the OE ignition wires typically last a very, very long time. 200kmi+ / 25+ years is not uncommon. The wires often get replaced by shops looking to make money, not because the old wires were bad. (Yes, there have been some documented cases of faulty wires with voltage leaking and shorting to ground, with visible arcing at night, but this is super rare IMO.)

Anyway - the wires in your photo are the aftermarket Bosch gray wires, which have very fragile insulation. The outer gray cover tears easily, but the primary insulation underneath should still be OK. I wouldn't bother replacing the wires just because of the one tear shown in the photo, unless there is visible arcing, or other problems with the wire set. And, I wouldn't buy the gray Bosch wires again.

Yeah I recently had one of those super rare occasions

 

[gsxr]

Thanks for advice. I was thinking the wires actually looked perhaps okay. So culprit is probably just the dust caps inside, I'll start there. I noticed that pelican lists all the Mercedes factory brand ignition items pretty much as not available.. what's best option now?

OE parts are still available, but $$$ from the dealer. Dunno why Pelican can't get them.

I like Beru caps, Bosch should be OK, some people like Bremi.
Get Beru rotors, they are OEM Doduco with Star logo and MB part number.
Insulators are only available aftermarket from Bosch.

 

[thulsadoom]

For completion.. which wires you like? Pelican has Karlyns for $190, while magnecor must think theirs are pretty special at $400 woohoo!

 

[gsxr]

I like Beru wires, which may be used on other brands of wire sets. However unless you can see a close-up photo of the wires, it may be hard to tell what brand of wire is used within a set. I'm not sure if you can still buy Beru-branded sets nowadays, I haven't shopped for them in a long time. $200-$300 is pretty normal, and IIRC the OE/dealer sets are $350+?