Engine and Transmission Tech

The cross-over passage helped animize the fuel for cold weather drivability; on older cars, it also worked in conjunction with a heat riser trap on one exhaust manifold to help create an exhaust bridge to channel the exhaust to the open side. Later on, it became part of the EGR system and also help with cold start with a surrounding water jacket to neutralize the resulting heat once the engine warmed up and helped cool the intake down. This passage would mostly end up getting blocked with nasty carbon and cause cracks at the bottom of some intake designs.

The guys are right, don't use it as you don't need it, besides, your intake is not designed for it.

I've been on and off reading your thread about your backfiring problem so, I don't remember what has been suggested or not. However, here's my 2 cents on some suggestions:

(1) Have you done a cylinder balance check?
(2) Have you performed a "cylinder leak down test"?
(3) I once had a newly rebuilt engine that would have a certain valve stem (on the intake side) occasionally hangi up in the guide, hence, causing popping (backfiring) through the carburetor. I don't imagine that would be your problem but just in case.
(4) Point a hand held digital pyrometer at each exhaust header outgoing tubes and read the difference in thermal efficiency of each cylinder; it could tell you a lot

I hope the comments help you diagnose the issue as I know how frustrating it can be.......

Jac

Quote:

Point a hand held digital pyrometer at each exhaust header outgoing tubes and read the difference in thermal efficiency of each cylinder; it could tell you a lot..

That would be a great idea.....unfortunately, typical infrared laser exhaust pyrometers (like the HF unit) won't read an exhaust header/manifold temperature > 500-600F. Normal running exhaust temps are in the1000F range.

You've got to be kidding; exhaust headers temperature readings are directly related to engine load. I don't think that Rob would be doing dyno pull in his driveway; all he needs to do is keep the R.P.M. up to around 2,000 to 2,500 RPM to come off the idle circuit (if carburated) and,, he should get readings around 600 degrees or below; every engine is different, I also assume his headers are Jet coated as it can reduce temperatures quite a bit. I've done this many times and it is an excellent way of picking out lean (or rich) cylinders.

I don't doubt that temperatures inside the headers (coming out the heads) exceeds 1,000 degrees, but we're talking sensible approach here. If someone wants to measure close to combustion temperature then he needs to install EGT probes; again, we're talking diagnostic tool.

I don't know what IR gun you own but mine goes up to 1,200 degrees and I only paid $150.00 for it and if you want to go up higher (2,000 degrees) you also can get one at a modest cost. My IR gun has helped me diagnose all sort of issues varying from A/C to, cooling, exhaust catalytic converter efficiency, tuning, brakes, and etc., etc., Here's a link to tons of IR type guns :
[www.transcat.com]

Here's also a Raytek owner's manual that depicts the different usefulness of such a great tool: [www.instrumart.com] (good reading material)

I hope that this clarifies the limits of a decent IR gun....... Good luck Rob!

Cheers,
Jac

Didn't realize that you had one of the fancy IR type guns, Jacques......most of the "budget' guns don't go past 600F. The better guns, like yours, are a great tool for isolating cylinder issues.

If anyone is interested, Harbor Freight is having a sale on a IR gun for $34.99. It goes up to 968 degrees F. Not the best quality but you can't beat the price.

[www.harborfreight.com]

Jac

Thanks Jacques, I'm pretty sure that's the same one I have. I didn't realize it goes that high though. It does seem to eat the battery even when it's off/not used so if you get one, take the battery out when you're not using it.

So, in the way of an update... With the plugs short gapped, they were all fouled or fouling -- not sure if they should have been or if that was maybe a symptom of the intake & headers loosening more while trying to diagnose things earlier?

But, I did get everything back together today & ran the car up to temp so I can retorque the intake & headers when it cools. I put the plugs (AGSF32C) at .044 [Have read that 302's seem to do better around .050 but sticking w/specs for now], reinstalled the intake and replaced my plug wires. Initial timing still @ 10*. I also worked on the header to exhaust pipe coupling to try & eliminate a leak there.

Won't know more till I take it back out on the road (waiting for my son to get home so I can check the speedo sensor wire while it's on the jack stands), but running it for a few mins in the garage, here's what I observed:

1. All 8 cylinders seem to be firing -- ranged from 350-425*. That was just random idle with occasional runs to 2500 or 3k RPM.
2. Played with accelleration & rapid decelleration & didn't hear any pinging, popping or backfiring.
3. Not sure it's 100% sealed, but the exhaust leak @ the header couplings is either fixed or very close to it. It's hard to tell in the garage, but I think I still have some exhaust leaks back by the muffler but will check those later.

I do have some oil & water on the garage floor I need to check out. I think the water came from a heater hose that was loose & I'm guessing the oil came from a socket that fell in my drain pan (it was barely big enough; oil was very close to the lip). But, will clean that up & see if there's any more when I run it again.

Since the intake gasket didn't show signs of a problem back when I pulled it, I'm hopeful that all that was wrong was the loose intake & headers, exhaust leaks, & probably one or more plug wires (haven't checked them w/ohm meter yet put plan to out of curiousity).

Will post an update when I get to run it later in the week.

Played with accelleration/rapid decelleration and didn't hear any

Has this story got a happy ending yet? Can't wait to hear.......I'm thinking air leak was the biggest problem

Quote: Has this story got a happy ending yet? Can't wait to hear.......I'm thinking air leak was the biggest problem

Well I'm delinquent in posting an update... But yes, this story does have a happy ending. Took two tries, but it is running much better now. I'm pretty sure it was a combination of both air leak and a couple of bad plug wires. Here's what I did:

Re-did the intake gasket using the fel-pro 1262S3 gaskets. Turned out the combination of the bigger ports in the gasket and my world products air gap clone weren't a good match. Remember I'd said I had some water on the floor? Well, th 2nd time I started it I had a spray of water shooting 10' across the garage. The intake casting curved down toward the back bolt by #8. I didn't notice when installing the intake but it left a pin size portion at the upper back corner of the water port in the gasket uncovered.

Since I had to pull it, & I was still concerned my drop base was contributing to the rich condition (I only had about 3/16" between the top of the choke horn & the bottom of the air cleaner cover so was worried I wasn't getting enough air in) - so, I did a sarch on craigslist & there was good condition Edelbrock Performer 289 intake for sale. I got that installed it - this time using fel-pro MS93334 gasket. It has similar composition but ports matched the intake & heads better.

I also replaced the plug wires. Later tested them & two are suspect. They're two of the shorter wires but resistance on them was double the longest wire.

And last, I took some time to get the exhaust leaks sealed up.

Net is it's running way better. All 8 cylinders are showing similar temps @ the header tubes, it's pulling stronger, the popping on deceleration
is gone, and the tendency to run on when I shut it off is also gone.

I'm going to drive it for about a week and then have another look at the plugs, but there's no doubt it's way better than it was. Thanks to all for your help!

Great job Rob. We all like a happy ending. Nothing conquers like persistance. I'm still working on the concept. Cheers, roverman.