Take the fuel injection system completely out of the equation.

I'm going to find a carburetor manifold and a carb, stick it on the engine and run it. If it's smooth, then I know the EFI system is malfunctioning. If it's still rough, then I know it's a mechanical problem with the engine.

Just have to find the manifold and some time.

So freakin' sick of this whole thing...

 

well unless u make a chip w/ out all the efi stuff then it will still run like garbage cause the wrong values in certain area dected will rich/lean out timing or add/subtract fuel...etc... i just hope u get it all figured out

 

Just force open loop and it should be fine.

-- Joe

 

for purposes of what he's testing, none of this should matter.

once you slap a carb on it, all the fueling is done.

as for the dizzy, two easy options: (1) unplug the ECM from it and let it run on the timing of the module (and for a simple idle test, you can rotate the distributor to any timing you want); or (2) drop in a regular weights n' springs HEI.

 

That was my plan.

I'll just pick up a cheap-a$$ mechanical fuel pump and push rod. A buddy of mine thinks he can dig up a small block Chevy manifold for me to borrow from a friend of his. Hopefully I can do the test for under $50 (including gaskets).

Man, I just need to know what to attack here... engine or EFI system. This is a test I should have run a long time ago.

If it turns out to be the engine, then more than likely the cylinder heads are the problem. Highly unlikely a relatively new ZZ4 is going to crap out like this. And the entire valvetrain has already been checked and/or replaced, including the cam itself.

If the EFI turns out to be the culprit. Then I don't know what to next... I can't be the only guy with a Miniram who's fighting something like this. Especially not with such a mild engine combo.

Guess I'll cross that bridge when I get to it.

 

Can you link me to a post describing your original problem?

-- Joe

 

Heheheheh.... just do a search on ULTM8Z and look at my threads within the last six months or so. Pretty much everything I've posted in the last few years has to do with this stupid problem!! But, the last six months would give a clear picture of everything I've done with respect to diagnosis.

 

Ahh.. I just searched your threads. Looks like your having the same problem that haunted me for the last year. Low speed crawl causing violent bucking.

I detailed a thread on it called "idling accross a parking lot".

Finally gave up, figured it was the motor.. The motor ended up exploding anyway at the track. So I built a new setup, same intake + tb.

Same issue..

How could that be? new cam, heads, pistons, bore, etc.. New tune, different bins.

After a lot of tinkering I figured out the problem. It was some relation between the motor and the throttle body/intake.

I *think* it was due to a very small throttlebody + singleplane style intake. (70mm monoblade). The 4bbl doesn't do it at all. Thing is great.

I'm also noticing that the 4bbl's progressive linkage is great. Car is VERY tame on the primaries, and an animal on all 4...

What are you running for a TB?

-- Joe

 

52 mm dual blade from SLP.

 

It would be more convenient if the problem was in the heads, but considering AFR has already been through them once, it seems at least somewhat unlikely. If it is in the heads, something like air leaking through a rocker stud (if I remember correctly, AFR's rocker studs protrude into the runners like my fastburns on my '71) would be my guess. If you're concerned that one head may be flawed, you could swap the heads onto opposide side of the motor and see if #7 starts running like crap and #2 comes up to normal.

If the problem ends up being in the shortblock, then i'm guessing some type of problem in the rings/ringlands. Since your problem started suddenly and out of the blue, you have to consider things which can suddenly break - rings and ring lands qualify. And since you haven't been able to eyeball them yet... they seem a worthwhile potential suspect for investigation.

look forward to the carb results

 

not to hijack the thread, but...

I've often thought that some kind of progressive intake setup would be great for EFI. That is one area where (IMO) carb still has an advantage - things aren't so sensitive/jumpy the first 1/2 travel.

GM solved it with the throttle by wire systems, but I'm not sure I want to hack that into my '730

 

Wouldn't a leak down test catch a problem like this with the short block? The leak down test wouldn't specifically point to it, but if something like this was present, wouldn't it cause the leak down test to fail?

One thing I want to do is get my AFS-74 sensor for the passenger side. I have a Bosch in there now, and it austensibly is telling me that both sides of the engine are running the same. But since I don't trust Bosch sensers anymore, I want to see what identical O2 sensors say about both sides of the engine.

My theory is that any malfunction on the passenger side should cause the ECM to react differently than the driver side. If both sides do in fact run the same, then I know I have a problem that is not localized to any particular cylinder. And the odds of every cylinder crapping out at the same time would about the same as Rosie O'Donnell getting under 300 lbs. However, if the ECM reacts significantly differently to the passenger side, then I know the problem is likely localized to one cylinder on that bank.

If I can eliminate the possibility of a bad cylinder, then it's likely down to just the EFI as the problem. And the carb test will either confirm or deny that.

 

I think I had mentioned it in another post somewhere else, but I do believe in failures that don't show up in tests, such as when my 406 burned a quart every 45-50 miles due to the wrong size ring (1/16 rings in 5/64 ring lands), yet passed compression/leakdown tests just fantastic.

did you ever get the chance to do that "first hit" compression test? I don't know how valid of a test it would be, but at the same time, if #2 showed a greatly different result than the rest, that would be another reconfirmation that the problem is on #2.

You've had a number of pointers at the #2 cyl (unplugging the plug wire to that cylinder not making much of a difference, and i think the injector wire too, and also the fact that the #2 header tube is cold compared to the rest). thats why i keep wondering about the lower end.

certainly the carb test will rule a bunch of stuff out! and at the same time, present even a bigger mystery if indeed the problem goes away.

If I remember correctly, didn't someone do some WBO2 data logs for you and you found that the passenger side measured quite differently from the driver side?

It might be worthwhile to sit down and write out all the "test results" onto a single page. You've done a lot of tests over the years(!), so time to compile the data and view it as a whole - not a series of individual tests.

from my memory of all the tests you've done, they all seem to have only one thing in common that could explain each result, and that's a problem in #2.

then again, I could just be paranoid since my problem was in the rings and it was a b**** to find, we ended up pulling the motor twice, and only doing the complete teardown the second time.

 

FWIW, I think lots of people are running a TB sized for strickly WOT racing, on a street engine. While in *theory* 100 K/Pa, would seem fine, in practice depending on all the normal variables, it might not be the best number. While everyone thinks about port/runner/plenum combos., the mean average air velocity is totally ignored. It's the inertia of the air, that needs to be looked at, since that's what dictates the cross fueling, and cylinder fueling.

I played with a number of throttle bodies, and plenum, etc., etc., I'm now back to the stock throttle body.
What real good is a throttle body, that has little to no response over 7/8 throttle?, while grande for the strip (maybe) all it most often does, is give a false since of buttometer performance, since you have soooo much more off idle air flow. Gotta remember, at like 30% blade opening, your at 60% air flow potential.

 

ABSOLUTELY! Butterfly throttles suck for this reason. Barrel throttles, they don't have the problem nearly as bad when designed properly and used with a 1:1 cam.
For all around power and precission using a special cam does help. I've looked into it because of my crappy TBI linkage (too sensative off idle, perfect, then no sensativity). It's all in the torque vs TPS vs RPM slope. I've got some data that I'll bring to you for review. I've also got some designs for building barrel throttles that will be smaller than your typical large butterfly. A buddy works at a machine/manufacture school and said he'll make some things for me . I'm hoping

 

I don't know... somehow I doubt a 52 mm throttle body is too big for a modified ZZ4 that's probably pushing between 380-400 hp. Besides, when it was running right many moons ago, the torque and throttle response was phenomenal. Oh, how I long for those days again!

 

I moved 86hp worth of air through a single 20mm hole. Smaller than a quarter. Stock F4i engines have 4 individual throttle bodies that are about 40mm stock and made 105hp. So if you look at it you really don't need much throttle body unless you're drag racing.
The stock 502 RamJet bbc that makes 502hp has a stock 48mm TB . So it might be safe to say that the 52mm is too big, but I think we're getting off subject. It's highly unlikely the size of your TB has anything to do with your idle.

 

It has 33,000 miles and #8 cylinder was not getting oil. now it needs to be rebuilt. does anyone know if there is a warranty for the ZZ4?
please help.

 

There is, but it's only 12,000 miles or 1 year, I believe.

What do you mean by the "#8 cylinder isn't getting oil"?