3.1L Build Woes - Setting Cam Time Question

[GTT]

I recently finished a top end rebuild on my ’82 3.0 and after weeks of trouble shooting, I am leaning towards my cam timing not being spot on. My question is after I drop the motor to check it, if I need to adjust my cam timing, do I need to install mechanical chain tensioners to tension the chain like I did when I set it originally, or will the carrera hydraulic chain tensioners I installed provide enough tension while I take my measurements and make adjustments if necessary?

The details of my build are as follows: I installed Supertec’s 3.1L kit (btw, Henry is awesome), had my cams reground to 964 profiles by Doughtery Racing, had the heads rebuilt, the FD and WUR rebuilt, new injectors, new airbox, all new vacuum hoses, new CDI, green wire, Clewet plug wires, rotor, cap, carrera chain tensioner upgrade, new fuel lines, fuel pump, fuel tank, etc. Installed SSI exchangers and a Dansk sport muffler. Basically, anything that could be problematic I replaced while I was in there. This car/motor sat for + 20 yrs before I got it and had some broken headstuds, hence the rebuild.

The symptoms I am having is that the car will start and run, but I get what sounds like a misfire and a popping sound through the exhaust at idle, under mild acceleration and deceleration. It also feels like it’s running slightly rough. The plugs on the left bank (1-2-3) look like they are burning properly, but the right bank (4-5-6) are almost wet looking like I didn’t get a good spark on that side. The right bank definitely is not burning as cleanly as the left bank. I know I’m getting a good spark and good fuel to that side, so the only thing left I can think of is that maybe my cam timing was off a little, despite obsessing over trying to get it right the first time.

I’ve checked the CIS fuel pressures, done a smoke test multiple times to rule out any vacuum leaks, and exhausted pretty much everything I can think of CIS related. I am not running an O2 sensor, and installed a wideband AFR.

-Troy

[mikedsilva]

That's interesting.

What does your AFR read on the wideband?

Can you pull the muffler and run it (loud I know) then have the sensor in each of the ssi outlets to see how much of a diff you have from left to right?

My (limited) understanding is that cam timing would need to be out quite a bit to cause the issues.

You might need to run a fuel test with a graduated measuring cylinder connected to each injector, to see if you have even fuel flow.

Just some ideas.

[GTT]

The wideband hovers around high 13s-low 14s on start up and settles around mid 14. I didn’t think about taking the muffler off to compare each side, but don’t see why I couldn’t. I have checked and rechecked the fuel flow using baby bottles and they all are flowing almost identical. The last few weeks have been a crash course in CIS troubleshooting. I’m really wishing I’d just gone with PMO’s now but have so much time and expense invested in making the CIS work, I’m determined to win this battle first.

[mikedsilva]

Ok so sounds like your fuel dist is delivering correct fuel and your injectors are not blocked if the volume delivered is consistent.

I'd tweak the CIS mixture screw maybe an 1/8 turn clockwise to richen it, while watching the afr. See if that helps.

To answer your original question, using the stock tensioners should be fine for checking your camshaft timing.
I would remove the engine, pull the timing and valve covers and before undoing anything, check everything. (valve clearances, then existing camshaft timing).

But the popping at idle sounds like it's lean. If the tweak of the mixture doesnt help, then I still suspect an air leak. somewhere.. although I know you say you've ruled it out.

Hopefully someone with a lot more knowledge and advanced diagnostic ability than me, chimes in soon.

[GTT]

Thanks for the answer and all the input. I’ll give that a try and see how it responds. I keep thinking air leak too but sure can’t seem to find it if that’s the culprit. I have smoked tested using a smoke machine plugged in to the brake booster line and haven’t found any leaks anywhere while blocking off the two lines from the back of the top hat and sealing the throttle body with a rubber glove. I have noticed there not much change in idle when removing the oil filler cap so perhaps I’ve still got a bad leak somewhere I can’t identify.

[stownsen914]

If you just want to check the cam timing, you should be able to check the intake lift at TDC on #1 and #4 while the engine is still in the car? Granted not the perfect way to check timing, but you just need to confirm it's not way off to rule out that possibility. I'd agree wtih Mike that it would need to be way off to cause the issues you're describing.

[PeteKz]

Agree with Mike and stownsen914 that the cam timing would have to be substantially off to cause uneven combustion on opposite banks. I know you are using 964 cams, but keep in mind that Porsche varied the factory timing on the SC/Carrerra cams by almost 1mm lift over the run of those engines. I think that equates to 2-3 degrees of cam timing. It didn't make the engine run richer or leaner. Thus, if your timing was off by that much between the banks, you should not notice it. But as stownsen suggests, it's not too hard to measure the timing on the #1 and #4 cylinders to check.

Also agree with Mike that you probably still have an air leak somewhere. Remember to cover the exhaust pipe with a glove too, so that the smoke is forced out through any other leaks. Adjusting the CO/mixture screw may also help you troubleshoot. If you have an air leak, It usually causes hesitation or uneven running or popping at low throttle settings. Those go away as the throttle is opened because there is higher air flow and lower vacuum in the intake manifold, thus drawing less air through the leak

On which side is your AFR O2 sensor installed? I'm guessing the 1-2-3 side.

I don't see how the fuel delivery could be the same on all cylinders, and you have wet plugs on one side and clean combustion on the other.
Possible explanations:
(1) you have a significant air leak affecting the 1-2-3 side, and you adjusted the CO screw to get your 14-ish AFR on that side, then the 4-5-6 side ends up too rich.
(2) Your fuel delivery isn't as even as you think it is. I know you said that you checked the fuel delivery through the injectors. How did you do that? You want to use tall and narrow collection bottles because that makes the differences more visible (I use test tubes).

[GTT]

PeteKz, thank you for your insight as well. Sounds like it's back to the drawing board on checking for an air leak and/or fuel delivery problems. Your comments on the usual symptom of an air leak is pretty spot on with what I'm experiencing - unevening running and popping at low throttle that clears up when the throttle is opened. Under hard acceleration it runs and pulls well, it's just at idle and low throttle that I'm getting the pops/misses. I did not cover the exhaust pipe when I did the smoke test, so I'll start there. If that doesn't result in an obvious leak, I'll pull the injectors and check my fuel flow for consistency again. And yes, my AFR is on the 1-2-3 side so your theory makes perfect sense. Work is going to get in the way the next couple of days, but I'll get to it later in the week and post and update.

[targa72e]

You should put a bung on the 456 side and see what the mixture looks like on that side. Might provide some more insight into problem.

john

[GTT]

Originally Posted by PeteKz

(2) Your fuel delivery isn't as even as you think it is. I know you said that you checked the fuel delivery through the injectors. How did you do that? You want to use tall and narrow collection bottles because that makes the differences more visible (I use test tubes).

PeteKz, I've been thinking about your comments and was able to get home early enough tonight to do some testing. I think you're probably right on the fuel delivery not being even is either a problem, or the problem. My observations suggest that at idle, not all the cylinders are getting an even fuel flow, but on WOT they're are pretty even. Here's what I did to test. I first disconnected all the injectors and placed the bare fuel lines in baby bottles, then turned the CO mixture screw until all 6 just started to flow to simulate low throttle/idle, and after about 30 seconds cut it off. For what I'm calling test #1, there was some deviation in the amount in each bottle.

For test #2, I did the same thing again but with the injectors installed. What I observed right away is that they did not all start spraying at the same time. 1-2-6 quickly started to spray while the others weren't even dripping. After turning the CO/Mixture screw further until all were spraying, I again let them run for about 30 seconds and 3-4-5 were lower in total volume.

Finally for test #3, I stated with the CO/mixture screw backed out so nothing was spraying, then lifted the intake plate to simulate WOT for about 45 seconds and then stopped. When I did this, the bottles were pretty close although #3 was about 20ML lower than the rest.


Based on these observations, my theory is that the Fuel Distributor is not putting out an even amount of fuel at low idle, but it gets better at full throttle which is why the engine seems to clear up and run under power, but not at idle or low throttle.

I've seen a few CIS videos on youtube that lead me to believe that all 6 should be putting out an equal amount of fuel, even when just opening the CO/mixture screw. If anyone has any thoughts, I'd appreciate any input. CIS is new to me so I'm reading and watching all I can find.

[Jeff Alton]

I know you said bank 1 plugs looked different from Bank 2, Pull them and post pics. You are doing lots of different tests, have put a 5 gas analyzer up the tail pipe to get a sense of the CO the entire engine is creating?

Sounds like a Vacuum leak, pretty darn easy to test for with CIS.

Or simply check cam timing if you are concerned, takes about 30 mins. Pull the valve cover, mount your dial indicator and turn the engine. Can easily be done in car.....

Cheers

[PeteKz]

GTT: This bottles look to me like a large difference in fuel delivery. Next time you test, fill them all the way up to the 125 ml line. The higher level will make the differences more apparent. That will take awhile with those bottles, which is why I use 10 or 20ml test tubes.

I don't remember if the FD in 1982 cars had the individual delivery adjustments on the top of the FD (I think not). Please verify and send a picture. If so, you can adjust it without removing it. I shoot for less than 2% difference in delivery between injectors. If your FD does not have the adjusters, then you should send it back to whoever rebuilt it and get it correctly readjusted.

As John recommended, you should also weld another O2 sensor bung into the 4-5-6 exhaust collector. I bought an AES AFR meter for my car several years ago, and many times I've wished I bought the 2-channel meter instead of the single channel meter. I did weld a 2nd bung into the 4-5-6 exhaust collector, so I can move the O2 sensor to the other side for troubleshooting. But it would be so much more informative to see the AFR on both sides at the same time, while driving.