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B23/LH 2.4 Rough Idle?

Tfrasca

Active member
Joined
Apr 20, 2015
Location
Ben Lomond, CA
I don't have a frame of reference for this. The idle on my 142 seems rougher than it should be. IPD cam advanced 2 degrees with Dale's gear, 60 lb Dekas, 3" AMM, Mike's chips. It currently has stock (not diesel) motor mounts.

In the video, it doesn't look like much, but it shakes the car and I know other 240s are much smoother. Spark plugs are new and at .28, cap, rotor, and wires are less than 5,000 miles old. Fuel pressure is rock steady and 2.5 bar right now, and at 3.0 bar it was the same. Any thoughts?


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Didn't look that bad, especially on stock mounts. I'm on diesel mounts and there's no NVH into the chassis. Mine's also balanced, but it has an underdrive on it, no balancer as well.
 
Didn't look that bad, especially on stock mounts. I'm on diesel mounts and there's no NVH into the chassis. Mine's also balanced, but it has an underdrive on it, no balancer as well.

Yeah, I can't tell why my car is shakier than other redblock cars I've been in. Maybe I'll go back to diesel mounts. I thought I remembered them being too harsh, but I also had other weird vibration-causing stuff going on back then.
 
I'm on diesel mounts, no issues at all. Only ones I had issues with were the Ireland E30 mounts. Those would rattle your teeth out at idle, fine from 1k on up, though a little more buzzy than the diesel ones.
 
I'm on diesel mounts, no issues at all. Only ones I had issues with were the Ireland E30 mounts. Those would rattle your teeth out at idle, fine from 1k on up, though a little more buzzy than the diesel ones.

Yeah, I think I'll go back to diesel mounts. I do think the stock ones transmit a TINY bit less NVH, but the engine rocks more and the weight transfer kicks the car around a bit. Pretty annoying.

I have noticed that the idle is drastically improved when LH is learning and runs rich. 13:1 seems to be the sweet spot.
 
Take a good look around for intake air leaks if the richer mixture makes it smoother. That is also something that makes the idle rougher.

How is the valve adjustment? Make sure the ignition wires are all seated well in the cap and on the plugs. In general though a B23 won't idle quite as smooth as a B230 because of the increase in crank counterweights and front damper on the B230. Plus the heavy dished flywheel all work to make it a smoother idle than the earlier engines.

Looks great!
 
Take a good look around for intake air leaks if the richer mixture makes it smoother. That is also something that makes the idle rougher.

How is the valve adjustment? Make sure the ignition wires are all seated well in the cap and on the plugs. In general though a B23 won't idle quite as smooth as a B230 because of the increase in crank counterweights and front damper on the B230. Plus the heavy dished flywheel all work to make it a smoother idle than the earlier engines.

Looks great!

I've looked extensively for air leaks. There aren't that many vacuum lines (wastegate, bypass valve, fuel pressure regulator), and they're all perfect. I actually did have a leaking brake booster, which would make my AFR go full lean when I stepped on the brakes. Obviously a huge vacuum leak. But I replaced the booster and that problem is solved. I've also done a boost leak test and everything held great up to 20 psi.

Valve adjustment is something I haven't checked since we put the head together. That's a good call. If the valves are within spec, I'll just chalk the idle quality up to being a B23 I guess.
 
Valves can definitely add to it. I could tell when I still had the SI's in my 531 when it was getting due, since the vacuum would drop, idle would get worse. I usually run around .015-.016" on mine, leaves a fine line between idle and power.
 
Valves can definitely add to it. I could tell when I still had the SI's in my 531 when it was getting due, since the vacuum would drop, idle would get worse. I usually run around .015-.016" on mine, leaves a fine line between idle and power.

Is that cold spec or warm? Also is it really as difficult as they say to get a proper measurement with the hushers still in place?
 
That car looks so very right. Way to go!

Another idle thought was that the cam is advanced 2 degrees. I am running my enem V15 advanced 2 degrees as well in the kjet 82 turbo. These cams are very close in spec. I must say that 2 degrees helped the B21FT run really well. Much better than when it was at zero but now after a couple of years using at 2 degrees. I would add more with a turbo engine.

On my 93 wagon I tried 6 degrees advanced with the same cam but n/a version. The six degrees really seemed to bring the power band down and smooth out low rpm power yet still let you rev out with much better high end power to about 5k to 5.5k rpms. I don't push the revs in the 93 too high. That is what made me think you may want to try six degrees advanced.
 
That is cold spec. Use those bent feeler gauges that are at an angle toward the last couple inches of the gauge. The hushers are smashed pretty flat after you start running the engine.
 
Not necessarily relevant, But I am with dl242GT, when I installed my IPD cam I timed it straight up, but after a while I changed it to 4 degrees advanced, a good bit of difference in the lower end for sure. If you're going to be in there checking lash it is only a couple more bolts to give it some advance.
 
Thanks guys. I may try another couple degrees advance then. I'm under the impression that advanced cam timing tends to have a rougher idle, which is why I didn't go all the way to 4 degrees initially.

I just ordered a 235mm clutch, flywheel, and a brand new T5z, so I may be taking the car apart soon anyway!
 
Add me to the list running at 4* advanced. Still sings to 6800 without any issue at all, but it pulls better down low.

Yeah, cold spec on the valves, hushers make a little difference if they are under about 10k miles on them. Quick check, see if you can move the followers down with 5-10lbs of pressure. If so, you can tell they are changing the clearance slightly. It's not bad to pull the cam, pull them, install, and just leave them out as well. I never bothered to install on mine, still runs pretty darn quiet.
 
Add me to the list running at 4* advanced. Still sings to 6800 without any issue at all, but it pulls better down low.

Yeah, cold spec on the valves, hushers make a little difference if they are under about 10k miles on them. Quick check, see if you can move the followers down with 5-10lbs of pressure. If so, you can tell they are changing the clearance slightly. It's not bad to pull the cam, pull them, install, and just leave them out as well. I never bothered to install on mine, still runs pretty darn quiet.

Cool, I'll probably dig into the valves tomorrow. Another question: do you need to reset LH when you advance cam timing? I'm getting so sick of the long learning period with this car.
 
I hardly ever relearn mine, honestly. Even flipping between pump and E85, takes 50 miles or so but that's about it. Getting a good baseline tune is a big help though, with the early tune I was running from Mike kinda being a PITA to learn. The new gen one I'm testing for him is worlds better actually.
 
Well this is embarrassing. I was grossly misusing my adjustable timing gear for the last several months. When I tried to advance it 2 degrees, back then, I left the belt on all the gears (cam included), and turned the motor until the "+2 degrees" dowel pin lined up. I'm pretty sure this means I've been running WAY more advance than is recommended.

The reason I found out is because I tried to use the same method to set it to +4 degrees, and the car wouldn't even start. So I started over, timed it straight up, and it fired right up.

Then I re-read the instructions and set it to +4 the correct way. Idle doesn't seem too different, but the power delivery is much smoother and it doesn't seem to do as much weird stuff with the AFRs as it used to.

Glad that was a cheap lesson...
 
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