Handy930

My 79 seems to be surging at about 2200 rpm. I don't hear a miss or sound change with the motor, but feel it. If I speed up it seems to go away and if I jump on the throttle it runs great. Any ideas what I should be looking for? Thanks for any and all thoughts.

Mark Houghton

Had the same issue years ago, used to drive me nuts. Steady throttle in like 2nd gear through town and I would get this barely perceptible surging.

I think it's called lean surging, and all you need to do is tweek your mixture a bit to the richer side. Of course, my memory isn't what it used to be so if someone wants to flame me and suggest the opposite direction, then please don't hessitate!

Handy930

That could be it. I reset my mixture awhile back and did lean it up a bit. Set it at about 3.8. I'll do a recheck and see what I have now. Thanks for the tip Mark.

Mark Houghton

3.8 what? As in 3.8 CO%? If so, that's plenty rich.

Handy930

Yes CO. Stock setting is 2.5 +/- .5 I believe. Someone somewhere suggested a setting below 4%. My mods are 1bar spring, exhaust, sport cams. Should I try to change to stock settings?

Mark Houghton

Many people run at around 2.5 to 3.0 (mine's set in that range somewhere, but anymore I just look at the AFR's). You might want to try leaning out a bit and see what it does to your surging, 'cause you probably don't want to go any richer than you're currently at. It wouldn't hurt to try both ends of the spectrum to find the sweet spot that works for your modifications...some experimentation necessary. I used to use a Gunson Gas Tester to sniff the exhaust, but again I'm just setting via AFR's anymore and have her idling at around 14.0.

Handy930

Mark, I will give it a try in the next few days and see what happens. I'll post the results.

Handy930

OK, I reset the CO to 3.0. No difference except maybe the surge seems a bit worse at 2200rpm. I will drive it awhile with some Techron and see if it cleans up. Any other ideas out there.

Mark Houghton

Hmmm....you got an on-board AFR gauge? Would be good to know what your mixture is doing at various rpm's.

Ignition timing checks spot-on? Is it advancing properly when you transition away from idle?

Handy930

Don't have an AFR. The car accelerates from stop no problem. No hint of anything not right. At 2200 in second and a stomp and away we go and all feels fine. I replaced stock cams about 14 years ago. They were from Windward and suppose to be sport grind. If they were wearing how would that show up? A friend sometime ago said never to use a regrind, but they were already in. I am planning a tear down for a reseal and whatever else I find this winter and would love to have it running right before I do it so I don't think I did something wrong during the rebuild.

Handy930

Mark, one more thing. At around 2200 and steady in 2nd, I will get an occasional pop out of the exhaust. This has not changed with the reduced CO setting, maybe a little more noticeable.

Mark Houghton

I don't personally buy in to the "never use regrinds" logic, especially if they were ground from new billets. But that's an area I know little about. A worn cam, I would think, would most likely result in just overall reduction in performance as lift and duration begin to decline. Anyway, I kinda doubt that's your issue, but certainly check them out when you tear into it this winter.

That occasional exhaust pop at a steady throttle could easily be nothing but a bad plug misfiring, or maybe one injector partially plugged. Again, it's important to have all aspects of the engine tune in top shape (ignition timing, valve adjusment, valve timing, plugs and wires, rotor and cap, WUR control pressures, leakdown test, injector spray patters....that kind of stuff) known and verified. You maybe should go through all those motions before you yank the engine, since it may point you to something best addressed with the engine out of the car. Or, if you have access to one, then put her on a dyno for a full checkout of the engine tune...could point to something.

Sorry I haven't been of much help. These darn cars can be real frustrating until you find that "Ah-Ha!!" moment. What will probably happen is that you'll yank the engine, do the normal reseal stuff, put her back in, she'll run like a champ, and you'll never learn what the issue was in the first place.

Handy930

Will let's hope the rebuild does it. I will pull plugs. I have new ignition wires,coil, cap and rotor. Could the CDI unit that is a rebuild be suspect? I will try my old original and see if it makes any difference. Thanks for your input. It is getting cold here in Iowa and the cold air and the turbo do make a difference. I need to get an after market IC.

Handy930

Just switched out the CDI unit and it did not make any improvement. I am thinking it is a fuel pressure problem. I have new pumps and filter, but wonder about the accumulator or fuel metering, relief valve, or WUR. Not much else me thinks.

Mark Houghton

Didn't think the CDI was the culprit, but good to put that one behind you. If you don't already have, you should buy the CIS fuel pressure gauge setup for checking system pressure, warm and cold control pressures, and boost enrichment pressure. That will tell you the overall health of your fuel delivery controls. A cheap tool compared to the cost of accumulators, pumps and the like.

Wish I could say that I'm still driving mine, but too much snow, icey roads, freezing fog, 17 degrees this morning. I think we're done for the year. Got Stabil in the tank, air in the tires, heat in the garage, trickle charge on, car covered and sleeping. Time to do a couple of mods that I've been putting off. And stay on top of a new issue...http://forums.pelicanparts.com/911-9...rds-death.html

While you're in there, you might consider checking the fuel flow on each injector. There's a really good thread on the topic over on Pelican if you search for it.