ULTM8Z

Well, I took the car over to Kevin91Z and DynoDon's shop and they were able to narrow down the problem! Finally some people that know what they're doing!! I've had the car in a couple of other shops and all I got was a big

BTW, a HUGE thanks to Kevin and Don who took time out of their Saturday to inspect my car. I knew if I found some good thirdgen guys, they'd be able to figure it out!

Anyway, they put a wide band on the car and found that the passenger side cylinder bank was showing a 17-19:1 AFR and the driver side had a 14-15:1.

We pulled off the #4 injector plug and the AFR shot up to well over 20:1. However, when we pulled off the #2 plug, not much change- less than a point IIRC.

Since I know I have good injectors, good spark, and a mechanically healthy cylinder, then two possibilities exist:

1.) Lack of fuel. There's a problem with the fuel rail where the #2 cylinder is injector is being starved. However, I inspected the rail a while ago and no such obstruction could be found.

2.) The #2 cylinder is getting additional air from some place, thereby leaning out the mixture or it's mixture is being robbed by another cylinder.



Question for the MiniRam guys

Have you heard of anything where a Miniram had a hole in it or crack or some other casting flaw where two runners would be exposed to one another? I'm wondering if somehow theres some sort of hole someplace that's screwing up the #2 cylinder.

I guess I'm due for another R&R on the manifold real soon.

Low C1500

Is the compressoin good on that cylinder?

Z69

This is a long story and just about every conceivable ? has been asked.

also

funstick

could have a bad injector. send the set out and have them flowed. also with the short miniram runners i have seen lots of fuel distrobution issue just like on the lt1 intakes. i usually have to runs lot of Accel enrichment to cover transienets and once engine speed picks up the a/f cleans itself up. what RPM is this lean spot occuring at ?

Low C1500

Have you tried switching injectors from the lean cylinder, with the good ones on the normal cylinders?

ULTM8Z

Guys. thanks. But believe me, I've done everything you're suggesting....

https://www.thirdgen.org/techbb2/sho...ight=%2Bultm8z

Low C1500

OK, I read that post, You've checked all your wires, but not sure if you've verified that there is no voltage drop right at the coil supply (with engine running at say 2000 rpm).

Me, I had a mystery problem all last year with my TBI injection, just seem to have a miss at high rpms. Now with the 750 carb one there, it runs perfect. I just got sick of telling people I had a 400hp motor , but with tbi it was maybe 350hp.

But don't get me wrong your miniram is a real nice piece.

Your idea on a fuel problem (shortage), seems more likely than excess air.

funstick

were are you located ??? i thought i saw dynodon's??we talking dynodon on the eastside of detriot ?

ULTM8Z

I'm in Southern California. DynoDon is in Orange County.

RednGold86Z

iTrader: (1)

Rocker stud protruding into the runner?
Too much porting near the pushrod slots?
Injector wiring not givin it 12v, and solid connection on the pulled low to fire side?
Warped head or manifold or mating surface (doubtful)?

I read and tried helping on the other post, too.

Could be the throttle body gasket, or IAC passages not ideally routed, favoring that cylinder.

At idle, injectors are hardly ever the same in a batch, even if they flow the same near 100% duty cycle. Check the O-ring on the manifold side - it could leak air in, too.

ANY vacuum fittings in the area?

Try running Open Loop and richening it up to just SEE if it goes away (if not, then it's probably ignition, or a really bad leak).

funstick

i can tell you with certianty i have seen minirams suck collant into the #2 runner. this will definately cuase missifres. pull the plug and check for a white deposit buildup. dont know why i didnt mention this earlier.

Sonar_un

This sounds exactly like my crazy mis-fire problem too.

The only thing I haven't done yet was change the injector from the faulty cylinder and move it to another one.

JPrevost

Have you pulled all of the connectors off and measured the resistance of each injector?
Check the dizzy cap and clean the rotor contact, make sure the pins aren't loose. I wish I could help you hands on but you've said that you've done everything so I guess it's time to sell the motor apart and start over .

Sonar_un

Funny how you say that JPrevost.. because honestly, there are days when I feel like doing that too :P

funstick

check to see if cylinder #2 is sucking coolant. ive seen some minirams with sealing issues around the colant ports and casting porosity issues to boot.

ULTM8Z

Funstick, that's interesting!

I'll have to check that.

funstick

did you see jeff blackburns red/cady z28 in chevy high performance back in october. the miniram on it had the coolant sucking issue and ive seen it on 3 other intakes. not to mention the countless casting issues ive seen with the miniram.

ULTM8Z

I assume the coolant was being sucked in via a poor quality intake flange?

The coolant passage and the #2 intake runner don't share any common walls. I would think then that maybe I have a hole in the runner somwhere that's sucking in air from somewhere else...

funstick

no the coolant was both being sucked from a non flat flange and to top that off it was also by my own account going through a porus section of aluminum into the intake valley.

mos90

would coolant cause a lean condition?

what would the spark plug look like?

the reason im asking is i have a miniram also and im backfire some through the intake.. still tring to figure it out. but the good thing is im not getting any water in the oil..

from what ive heard about the miniram is that at idle is not uncommon to be leaner at the #1 and #2 cyl. than the in the rear. especcially with a bigger cam.

ULTM8Z

Well, I took the throttlebody off and grabbed an inspection mirror.

Looking down into the #2 intake runner, I couldn't see any holes or casting flaws whatsoever. Nor is there any evidence of any water getting into the ports. If one thing is good, it' that the problem is on the number two cylinder amd that the intake runners are so short- makes inspection possible without removing the mainfold!

Anyway, I also pulled the fuel rail off again and inspected for blockages and then swapped the #2 and #4 injectors again.

Still the same thing... miss on #2

One interesting thing though....

Using the inspection mirror, if I look at the cylindrical machined surface on the inside roof of the intake runner (where the injector machining tool cuts through), the residue of the injector spray pattern seems bigger on the #1, #3, and #4 than it does on the #2 port. Kind of odd. Yet if I look down through the #2 injector hole in the manifold from the outside, it looks no different than #1, #3, or #4.



Question- what would happen if an intake or exhaust valve were hanging up (not closing fully during engine operation)? I already readjusted the valve lash as well as did a leak-down test and it passed, but what if the valves hang open when the engine is running (if that's even possible)... problem with the guides or something? Would that cause the problems I'm experiencing?

funstick

it is entirely possiable to for a valve to not close fully during engine operation. i assume your running a hydrualic cam of some sort. if so pull the valve cover and lash the valves on #2 with the engine running and see if you can fix the missfire. i have seen some lifters that wont lash with the engine off and will hang a valve open. its rare but what are the odd of having and odd missfire. have you tried changing the plug and the plug wire for cylinder #2 only ? cracked plus open wire same thing also have you checked the wiring for the injector on #2 to make sure that the injector is recieving a good pulse ? could just be a bad splice in the harness. if all this stuff checks out then its time to look at adding some fuel in the Ve table run the rest of the motor a bit rich to cover the lean hole.

Gearhead143

Has any of these shops run a vacuum wave form? you will be able to tell the mechanical side of things and quit geussing. also useing a lab scope you will be able to watch the pental open and close and compare to another injector, compair pw on 2 or more injectors depending on how many chanels it has.

funstick

a 200cc iake port a miniram and a fiarly large cam should make it difficult to grab anything meaningful from a vacum wave form.

ULTM8Z

funstick, actually my setup isn't that radical at all. It's a 180cc intake port and a cam with only 212° duration @.050.

Also, if it's running so lean on the passenger side, you'd think that if I upped the O2 bias at idle to .750-.800 mV, it would start to smooth things out, but it doesn't. I've swung that O2 voltage bias in the constants table from .200 all the way up to .800, but it doesn't make any difference.


I was really racking my brain a little more over the weekend and I began to remember that even before the really bad misfire problem started up, I would get wierd a thing happening. Such that right after a warm restart, it would have a noticeable miss at idle for about 5-10 seconds and then it would smooth out and run just fine. Now, it wouldn't do it on every restart, but sometimes. I also began to wonder why TPIS didn't put a fuel cross over in the front of the fuel rails like the OEMs always do. Could there be some sort of vapor lock situation going on resulting in a partial starvation of the #2 fuel injector at idle speeds? Just grasping at straws here...

Z69

I read a post somewhere by someone doing there own rails that wanted to know if they needed a crossover. Wanted to save money on the fittings.
The reply mentioned something about vapor lock caused by stagnant fuel at the end of the rail not being flushed.

Slow89Iroc-Z

Have you tried swaping injector plugs from 2 to 4 to see if there is a problem in the wiring?

RednGold86Z

iTrader: (1)

You're probably on to something. Deadheaded fuel rails have to pass any vapors through the injectors and can run like crizap until they do. It may be a little dangerous, but you could try taking it out for a solid pull and then letting it idle. Or, add a makeshift crossover, or rig some wires up and fire that injector for a good second or two to pass the air. The air/vapor might never pass if it's at the end of a tube, though, and all it takes is a system pressure loss and some heat to vapor lock it up again. I can't say I really know how the OEMs are tackling this problem, with the deadheaded systems, other than better pumps and regulators that never lose pressure.

Z69

I thought about it a little, and I don't have a good feel for the
vapor curve vs pressure for gas. But a little bit of air could get in there over time. No where to go and this is a retro fit app. Don't recall your whole setup since it's a 2nd gen.
And I am exceedingly jealous that a 3rd gen fuel p/u fits your tank and not mine.....

ULTM8Z

Sorry about that...

I was also noticing the following as I drove around this weekend:

1.) It's somewhat rough when it's cold - something that could be attributable to the tuning (assuming the misfire doesn't exist at that operating condition). I haven't spent a lot of time on tuning the cold start because I was waiting until I solved the misfire problem rather than attempt to tune around it.

2.) There's a brief point between cold start and fully operational where the misfire seems like it goes away. At that point, perhaps the engine is warm enough to be in closed loop and have ECM control over fuel, but not so hot as to cause potential vapor lock in the fuel rail. If you look at the TPIS fuel rails, they are a big ol' honkin' heatsink. All that thick Aluminum... absorbs heat like a sponge!

3.) From a geometry standpoint- the #1 injector is very close to the end of the rail, much closer than #2's proximity to the end. I don't know how the fuel would behave differently between these two. However, a cross over between the rails at this point would nullify this condition.

I could probably rig up a cross over by putting two 90° 1/4 NPT's-to--4 AN fitings on the end of the rails. Then run a braided line from one rail, pass under the throttle body and than back up to the other rail. Hmmm....

ULTM8Z

Well, I just got off the phone with TPIS...

They said they never came across anything like a vapor lock situation.

I'm not ready to rule it out though, just based on that. If I have vapor lock, there has to be something different between the configuration on my car vs that of every other Mini-Rammed third gen Camaro/Firebird or a C4 Vette. If it's not the engine itself, then it must be something peripheral- like maybe the fuel lines.

Question: On C4 Corvettes, I know the fuel lines come into the back of the rails. Do the lines pass close to anything hot, like exhaust pipes? My lines (for about a few inches) pass close to the passenger side header tubes before coming up the back of the engine and entering the fuel rails. Could that be excessively heating up the fuel? Then in the rails, it absorbs more heat and produces a vapor lock situation? I do have some heatshielding around the lines, but maybe that's insufficient protection from heat?? Hmmmm..... maybe before I start adding cross overs, I need to relocate the lines a little??

Slow89Iroc-Z

I think you are over analysing the problem.... check the injector wiring, reseal the manifold, check for oil or water in the cylinder, check the valve lash, bent push rods, lifter, etc. first before we break out the physic books here guys.

ULTM8Z

I've done all of that... twice or three times in some cases. That's why I'm looking at seemingly ridiculous possibilities.

JPrevost

Here's a free idea, where is the primary on the collector? Is it the lowest point where water could be collecting?

Z69

After 6 months, water would show on the plug,
on the piston etc.
I don't know for a fact, but I don't think you'll get vapor at 43 psi.
Take a look at the crossover on a HSR if you need an idea.
Very similar manifold.

JPrevost

I'm talking about the exhaust... hence the mention of the collector. The plug shouldn't show water, neither should the piston.

If there is water in the collector and it's blocking the primary it would show up at idle when the water could accumulate. At higher engine speeds the water would be blown up the exhaust and into the muffler but only to later travel to the lowest point. This is the only thing I can think of that would cause your problems. A clogged primary does what you're suggesting is happening. If anything else comes to mind then I'll post.

Z69

Have you read the whole post(s)?

Good thing it was free...

JPrevost

I've posted twice as much as you on this topic . Is that a good enough comeback or should I waste more of our time?
I'm still waiting for a reply about the collector and yes, water in a low spot on the exhaust can kill distribution at idle. There was a cop car infront of me 2 days ago on an incline and the car stalled. It had been idling all day inclined and near the end of the day it got "worse" according to the cop while we were pushing it to the side of the road. We finally got it started and he just floored it. As he accelerated TONS of water came out both exhaust tips. It looked like a couple gallons of water had been the problem. That's just the one story about that. The other time it's happened to me personally was in a race car with upsweep header and a faulty shut-down ecm that hung the injectors that were open... open. It also left the fuel pump relay energized. Needless to say the engine was hydrolocked, plug removal, crank gas everywhere evaporate, grab extinguisher just in case, plugs back in and crank... stall, crank again and open the throttle some more to clean the plugs... POOF, fuel everywhere from what had to be about a liter of gas collected in the header.

Although it's doubtful that it is this since the wideband would just be reporting the air/fuel from the working cylinders . And if they're lean then it's obviously a problem with the fuel/air.

ULTM8Z

Well, I went under the car last night and I didn't see any low spots on the header tubes where water could collect. None of the tubes were damaged or showed anything out of the ordinary. This weekend, I hope to re-route my fuel lines. We'll see what happens with that.

ULTM8Z

Well, I rerouted the fuel lines and there's no change. Oh well.

ULTM8Z

Here's another off-the-wall idea...

How many people are running MiniRams with no cats? I have probably almost zero backpressure. Could there be some sort of excessive scavenging going on with the #2 cylinder?

69 Ghost

iTrader: (1)

Here is one that I have not seen posted yet. There is a known problem with LT1's and split blms. The LT1's have dual O2 sensors so it is easier to pick up on. The LT1 intakes also have different throttle body and it lines up with a hole that splits into little holes in the runners. These holes are where the IAC air goes along with the EGR. What happens when people start camming LT1 cars is the blms will split where one runs real lean and another runs real rich. Problem is you cannot tell this without having a O2 on both sides or you need to take it to a shop to tell. The cure is to adjust the TB blades while looking at the blms on both sides. There are other fixes but the bottom line is it appears that the short runners tend to favor one side for the air. The basic cure is to try to run about 30 steps at idle this appears to be a good place to start. I know this is not a LT1 but a miniram but it sounds typical of the LT1 intakes. Here is a link:

http://para.noid.org/~lj/

JPrevost

Here's how GM thought the Lt1's needed adjusting at idle.
I don't know what GM thought about the L99 (mini Lt1) or the 93 Lt1 but this shows a good trend. Also, early years didn't have any off idle offsets but the later years did . As would be expected through looking at the intake design, they richened up the 1 & 2 the most, then 3 & 4. It's pretty cool looking at it and figuring out when the intake valves open.... makes me think I want an Lt1 computer when I go StealthRam .

funstick

getting a monoblade tb will fix the split blm issue on an lt1 no problem.

JPrevost

Got any proof? Also, wasn't the IAC on the back of the TBI an issue where some people were adding pipe to help it out.
Physics is telling me that you've overlooked something you said you've tried. I'd go back through the list once more starting from the top. The only thing we know for sure is that cylinder 2 is funky by the pattern in the intake port. Valve operation, exhaust valve not opening or not closing completely, intermittent wiring, intermittent injector . Last step is reverting to tearing it all down to find the problem. Bent exhaust valve?

69 Ghost

iTrader: (1)

Here are someindividual cylinder multiplers:
Cylinder Multipler At Idle Off Idle

95 Caprice Cop 94Z28 Carpice Z28
1 1.10 1.03 1.03 1.00
2 1.07 1.00 1.03 1.00
3 1.02 0.97 1.05 1.00
4 0.97 1.00 1.00 1.00
5 0.98 0.97 1.03 1.00
6 0.99 1.00 0.97 1.00
7 0.90 0.91 1.00 1.00
8 1.07 1.00 1.00 1.00

for a 94 Z28 the off idle is 1.0 across the board off idle. As for the 94 PCM all somebody needs to do is convert the opti part into a distributor and then a crank position sensor. This would give everybody a sequential injection with a 4l60+ tranny control.

funstick

im refeering to the oval monoblade from az speed and marine. ive put them on 2 lt1 383's and the split blms magically went away. also on the az marine tb the iac orifice is in the center of the tb just below the blade. and with the wide opening it get a nice even amount of flow into the plenum. even at 1300cfm the engine responded well and i had to go rework the fuel trim cylinder to cylinder. of course your results may vary. these were car with mild cams. 215 @ 50 500 lift or so. they were closed loop tunes. they both run well.

JPrevost

If you wanted the values here you go; Draw your own conclusions.

327_TPI_77_Maro

iTrader: (8)

JPrevost, good to hear you have seen the light and are going Stealth Ram!

funstick

put a large cam in a lt1 and really watch those values change at low rpm. the problem with crutching the low rpm with that fix however has been lean/rich cylinders higher in the rpm band,hence why it was easier to fix the problem by correcting the airflow dirtobution issue.