I hinted at this in another thread but I think it's deserving of its own.
My car, whether just sitting in park or out on the open road, won't rev past around 3,300 RPMs. Once it gets there, they drop back down to 3,000 like it's been choked, and then it'll just bounce and forth between those two figures as long as I've got my foot on the gas.
I just today installed a new distributor cap and it also has a very new rotor, plugs, and wires.
Perhaps something that's relevant is that on a hunch I took a peek at the contacts inside the new cap and even after going for a test drive around the block they are already showing black spots on them. Seems not right.
So, it needs a new coil, or? I've read up on some similar issues but most threads seem to become abandoned. Sounds like it could be anything from the cat to the fuel pump, but I somehow suspect ignition. Eager for any input. Thank you!
Air filter is not brand new but clean, and certainly nothing is clogged. But I guess a good way to rule it out would be to pull the whole thing off and fire her up as a test to see if anything changes. Now that you've got me thinking about it, the two big, black plastic hoses that connect to the air cleaner on one end and up near the radiator at the other weren't installed when I bought the car. One of the first things I did was put a pair back in, if only for aesthetic accuracy. Now I wonder if they weren't off for a good reason. Easy enough to find out tomorrow.
Check the rubber boot under fuel distributor .Its may be sucking air . And check the small micro switch on the bowden cable .By the way your doing that engine no good at all reving the b off it like that. Will it do the same on the road .They do have a limiter on them .
Oh, I'm not doing it much. In fact, I never realized I had a problem until I was testing an adjustment to my SLS. Someone said you may have to rev it up really high for the adjustment to take effect, so I gunned it and that's the first time I even noticed the issue.
Thanks for the links, bondavi. Although my car does not really behave like the one in the video. It gets to 3,300 and then drops off to 3,000, and then will bounce back and forth "vroom..... vroom.... vroom..."
I wish the FD was easier to test. I hate issues like this where you "throw crap at the wall and see what sticks." It's not like I'm made of money, but who is? I'll at least crack the lines and see if I can't eye ball the amount of fuel coming out for obvious issues.
I'll take a look at a few of the other things as well.
Trevor, yes it does it on the road or while parked. Can you tell me more about what and where this switch is that you suggest I check?
I cracked the lines on top of the FD one at a time and fuel seeped up between the line and the fitting slowly. The each seemed to do this at the same rate from what I could tell, and the performance of the engine died down each time. Not sure if that says anything.
But there is one important thing. I noticed a black box on the right side is wet with what smells like gas. Apparently this is the EHA valve. What does this do, why would it be wet, and is it my problem? See photo.
Also, I noticed someone in the past got lazy and didn't reinstall a couple bolts. I don't think this is enough to create a vacuum leak but what say you?
I included a couple general photos as well just to see if anyone spots something out of place.
After doing just a little reading on the EHA, it seems it may well be the source of my issue after all. Wouldn't that be something? May also be related to the slight rumble I have another thread about.
I'm going to pull it off just to examine the o-rings I'm told should be there, but I fear the leak may be something more than that which would require a complete replacement.
In my experience, removing and reattaching the EHA can make them want to leak more when they're old anyway. You can just buy new ones from MB so I ended up doing that. I suspect ethanol kills the internal membrane on them.
My SEC hesitated badly once warmed up and had surging acceleration on the motorway, because of the EHA.
Looks like a new one is pushing $300. I'd buy one happily if I knew that was the issue, but I have a feeling it'd be yet another example of me saying "well, it didn't fix my problem, but I guess it's nice to have anyway."
I don't think I've mentioned it but the car DOES sound a little hesitant/rough when starting it up. Sometimes, albeit very rarely, it will even die and I'll have to crank it again. So I really ought to try a new fuel filter; I've just been putting it off because the fittings, clamps, and so on all look like they'd sooner snap than loosen.
But first I should probably do a volume test. I am correct in thinking that the place I want to test is off the diaphragm canister to the left of the FD?
If it revs freely, no load and under load, then falls flat at 3000 RPM, I doubt it has anything to do with fuel. It wouldn't perform nearly as well under load if it was. It could be ignition since the rate of firing is directly related to RPM, or it could be the rev limiter (OK, I guess that would technically be fuel...). Coils can break down as rpm goes up, as could the ignition module.
Looks like its time for you to build a "get me home" kit which at the same time enables you to do what most of us do for our cars, while at the same time shotgunning your troubles
- Fuel pump relay
- Coil
- EZL unit
- OVP relay
- FD with EHA valve
Go find a junkyard and these parts should cost you $100-125. The bonus is you have a kit built for your car while shotgunning the repairs.
I wonder if you sprayed ether into the intake while it was at the 3k mark, if revs went up then you have a fuel problem. If not, either ignition/blockage of exhaust...
Sounds like a trip to the junkyard is indeed in order. I kind of hate going because the closest one worth going to is an hour away, and you usually get there just to find that the parts you need are the same ones everyone else needs and they're already gone. But I can't just keep throwing new parts at it, so scoring some used ones if only to experiment with is going to have to cut it.
John350, what you said about the fuel vs ignition system makes sense when you put it that way. I think the coil is the last thing to try, but maybe the EZL, too. I bet a junkyard car has a decent chance of still having both.
Are these parts the same for any 8 cylinder or does it have to be a 560?
All of those relays transfer between V8 models, OVP can be used across all models. On the fuel pump relay, you should avoid aftermarket relays and pre 1986 OE relays as these tend to not have the transmission kick down circuit. I have a rev limiter issue that is very similar to yours except that it occurs at 4500 RPM, which is due to an aftermarket Kaehler FPR, but I live with it because the only time I rev the engine past that point is if I drive on a race track (doesn't happen often) and the car seems to like cold starts with this relay better than my 3 other spares.
One easy check to perform is to run the engine in the dark and look at the coil, distributor and plug wires. If you see sparks jumping you know where to start.
I suppose it's possible the crank sensor is breaking down, too, although they tend more to be on or off.
I'm no expert, but the coil could be the same for many models, maybe even 6 cylinders, but it doubt the igniter (ELZ? I'm NFG at TLA's) is as it also provides the advance curve, which is probably engine specific.
Well maybe I'll get proven wrong right now, but I definitely have never had that button before. I was an administrator of a forum myself for years and I've repeatedly searched high and low here for the Edit option to no avail. Weird.
Since the forum look was 'updated' some functions using the old skin are no longer supported. Like on the old skin changing your password via 'user cp' the 'save' button may not come up etc.
I'm on the 'classic' and nothing has changed for me.
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