Ok you'll feel like me maybe at the end of this post..many mechanics do right now. I have a 1992 RS that was originally a 305 car. I bought a wrecked Z28 from the local auction and swapped out everything and I do mean everything from it to my car. Dash wiring rearend motor suspension anything that was better than what I had. Motor is dead on number 3 and 5. We have great compression and vacuume, we have spark, we have have fuel, and we have pulse. I have had the injectors replaced tested rebuilt everything so we know its not the injectors. Thought it was voltage of the pulse, so we changed the computer, no go, we changed the plugs, the distributor, fuel pressure regulator and rails. Heads and valve train good as well, but still its a v8 that runs on 6...it runs great on 6 but I'd prefer all 8...any help I'd GREATLY appreciate it.

 

you need to noid light each injector while its plugged. could be electrically "open" injectors. could even be bad harness splices where all the injector power feeds come together

 

Well, there must be a problem in wiring somewhere, it happens when you swap harnesses some times.

 

Plug wires routed to the correct cylinders?

 

Did you check continuity on all the plug wires? They often come brand new out of the box with breaks in the wire.

 

Like I said, I have done everything everyone mentioned so has the shop that its at...it all checks out good..wiring pulse plug wires all good..like I said a head scratcher

Hey Damon..did you use to live in Pcola and work at O' Reileys?

 

i would tell you to first get it out of the shop... they obviously dont have a clue... if you have fuel/air/spark the cylinder fires if it has compression... so atleast one of those elements isnt present in the combustion chaimber at the right time...if the shop is telling you they are all there they are lieing or ignorant to the fact that they are not...either way not worth the $90+/HR labor...

have YOU and i do mean YOU ran the car with the driverside valve cover off?

also how did YOU (and again i do mean YOU) determine that the 3/5 were not firing?

next fix your plug wiring 1,8,4,3,6,5,7,2

 

First the shop its at charges me next to nothing, as I am in the automotive field and run a transmission shop. I myself have performed all these tests along with the guys that run our Pro Mod proffessionally, so this isn't some at home in the backyard under a shade tree type deal. I am being as serious as possible...theres not an ASE or non ASE mechanic in Pensacola,Fl. that has been able to figure this out, so I am extending it to the world wide web to see if anyone else has had this occurance. Building another motor is not the answer because if its not mechanical then it will be a waste, if its electrical then I have a perfectly good motor..but again scratching our heads because neither seems to be the problem hence my and everyone who goes near the car fustrations. How do we know 3 and 5 are dead, 1. Headers can be grabbed with your bare hands after running 30 minutes or more without burning your hand off, 2. brand new plugs put in after running it all over town and they look as though they just came out of the box, 3. runs like it has a major mis but will still run just real rough. So here I am back at scratching my brain....so please understand my fustration and understand that even with the 3 major components which turn a motor those 2 cylinders are still dead..thats the puzzle we can not figure out because theoretically it should not have one of the 3 and boom easy fix. We have tested with noid lights and have pulse, we have tested the current to the injectors and have the same as the other 6 which are working, we have ran the motor with the valve cover off and watched the valve train all move exactly the same amount, we have changed the injectors as well as rebuilt and flow tested the o.e. injectors, we have put an inline spark tester on and we have spark, we have compression checked the motor with the plugs in and out, we have vacuume checked the motor and are good there, we have replaced the plugs and wires, we have even replaced the distributor, and we have scoped the passage way and its clear, we have checked the fuel rail for blockage and its good, and we have put a brand new TPIS adjustable fuel pressure regulator, so again We are lost...

 

i would run a leakdown test, not compression test, and monitor cooling system pressure while fully warmed up. start engine after reinstalling plugs then rev engine and watch pressure guage for needle flicker. retorque head gaskets?. maybe vacuum leak at manifold base between intake and head at the top? (loose intake base bolts into head)
could even be a cracked head, (chambers to egr passage)
some more ideas. HTH

 

have you checked the FIRING ORDER...

DONT go re torquing headgaskets if they are not ment to be... cause if you didnt have a leak before you will after...

leak down test isnt going to show anything at this point... he says that it has compression... even if it isnt 100% perfect it should still run...

again with all of this wicked smart edumacated people i wouldnt be surpised if it wasnt something like your FIRING ORDER

 

Do the plugs in 3 & 5 come out wet with fuel and clean or dry? If they are wet with unburned fuel but clean then the injectors are working and the ignition isn't firing them. If they come out bone dry then there isn't any fuel getting in there for some reason-they should smell like gasoline. Have you tried using those cylinders to trigger a timing light? Look inside the distributor cap for carbon tracks-the spark for those cylinders could be getting diverted to other cylinders. Have you tried swapping components around like injectors/injector pigtails/plug wires to see if the problem follows them? Some ignition problems will test ok static but manifest themselves when the engine is running.

 

The plugs come out dry, but we scoped the passages and they are clear, we've flow checked the injectors and they are at 55 like they should be. We have swapped injectors, injector wiring, plug wires, we've really done it all...thats why I am scratching my head and so is the shop. Has a brand new distributor and cap and module, so thats clear and you can put an inline spark tester on and they fire everytime as they should. Firing order is correct, I don't know why everyone keeps asking that as its the very first thing that was checked...start simple then work to the hard stuff. I am thinking intake gasket or cam. The valve train is moving the same amount all the way accross however it still could be a worn lobe or 2, but movements good so go figure. The intake has not been off so that could be an issue but you never know. Thats why I am wondering if anyone else has ever ran into this. Everyone that has had similiar symptoms wound up having a wiped cam, but it was very noticable in the valve train, this has no evidence that the valve train is damaged as it all moves freely and in tolerences.

 

diagnosing a car without seeing it is hard, since you have checked compression and spark, and the plugs are dry, i would do one of two things at this point, i would either (this is preferable) remove the injectors leave them connected to the car, ground the ignition so it WILL NOT spark, then turn the engine over to see if the injectors spray on the car (yes i see you used a noid light and the injectors were cleaned and checked off the car) or you could disable the spark and spin the engine over to see if those plugs are equally wet as running cyls. I would rather do the first method, because then you can also look into the intake port with a mirror, and see if there is buildup on valves (i am not clear if you inspected this already so dont jump all over me) there has to be an explanation for this.

 

I am no guru but this to me seems very simple.
You have a fuel delivery problem. If the plugs arent wet you have no fuel.

Either the injectors are not firing true or something is blocking the fuel getting to your combustion chamber

I know that sounds simple but that is all it can be at this point. Swap your injectors around and see if it follows. If it does not it is a blockage or your wiring is not good enough to carry the current needed to actually "open" the injector.

 

OR the firing order isnt correct... and you are firing those cylinders after the exhaust valve is open burning off the fuel but not making power

 

Newbie here but here are my .02, do a leakdown test on the affected cylinders since they are adjacent , it could be a head gasket allowing good compression on both but individual leakage .

Man it just sounds like a fuel delivery problem , since the pluge are dry but I just can't get the ignition plug wire routing out of my brain.

Bottom line as these guys already stated 3 things are needed for combustion ,there is obviously 1 missing .

I know most of this is redundant but there is something missing from the equation.

TOM

 

Thanks for all the input, but its all been done....hence the head scratching>>>> We have a local wiring guru come out this week to look at it and see if he can find anything. We went right to the injectors when we found the plugs dry and we cleaned and blew through the fuel rails, as well as take the injectors back to be checked and rebuilt. It doesn't matter what injector you put where or swapping wires, its the same results. As for a head gasket it can't be, no steam and we compression checked with all plugs out, so it would've backed into the open cylinder. As soon as its fixed it will be posted so no one else indures this hell.

 

just so you know it will be the plug wire routing that is the only way to explain it... do to the fact that if you swap the 3/5 plug wires both cylinders will be firing on the exhaust stroke burns off the fuel and still seems like a miss

 

While i cannot help in the solution to this problem, I know where you're coming from. My 2.8L V6 seems to have the same problem (except on the 4 and 6 cylinders). It runs like garbage, the compression is good, the spark is good and in the proper firing order, the distributor cap and rotor are good, and the #4 and #6 cylinder's portion of the exhaust manifold is cold after running for 25 minutes, while the #2 cylinder portion of the exhaust manifold is warm. And nothing I could do could solve the problem. That's when i decided to swap in a carbed 350, lol.

~Steve

 

do u no what no cilinders its not working on. wait did u say all plugs are dry?hmm are u sure ur valves are opening how does it sound like a 6 banger? if so this problem could be in the sensors mine ran like crap for a while more like a 4or5 banger tho coolant temp ssnsr was to blame check all the plugs does it smoke when started do u have to give it throttle to start? i have alote of exp with third gen camaros talk to me ile help ya
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and what year z28 did u get this from?

 

first thing to do is forget what ever has been done, ignore all that stuff. look at the problem like you never saw it before (by the way ase certified master tech, with l1 and a couple machinist certs for fun) if the oh i did that keeps coming into your mind forget it, alot of people will chase their tails for hours on something, cuse well i checked that. going by what i have read, you have a misfire on two adjacent cyls, and the plugs are dry ok i will give you a dumb test. unplug the injector, plug something in so you can turn it on manually, then start it up, turn the injector on, does it run? if yes go back to my previous post and tell me the answers, if no its mechanical or ignition. calm down and use logic, if you had done that you probabl wouldnt have wasted as much time. i dont know what parts you did or the shop did but from here on out, think nothing was done. (welcome to problem solving 202 the class after no one can fix it)

 

ive seen this before

 

The cases (good compression, correct spark, fuel and a miss) that I've seen were not firing because they were too lean due to a vacuum leak.
Here's the best way to describe it:
All the other 6 are getting a normal amount of air to put with the "idle" amount of gas coming from the injector.
The other 2 have twice the "idle" amount of air going in due to the vacuum leak and the mixture is too lean to light off.
This explains the injector firing normally and the plug being dry.
To verify/eliminate this do a WOT stall test if it's an auto-trans.
Those 2 cylinders will come to life. With a full air charge and a full fuel charge; the vacuum leak won't have any effect with the low manifold vacuum.

 

Or maybe the cam lobes are worn on 3 and 5 but not enough to start clicking.It would still pass a compression test! Or maybe the rocker nuts have backed off enough to not let much fuel in.

 

He checked that.

 

u sure it aint something dum like the dist cap open it an look at contact my bro broke a cap cause it was put on wrong the rotor botton hit it and riped the terminals of

 

Did you ever figure out you problem?

 

Just a thought.

check the intake runner gaskets, and check for cracks in the upper manifold between the runners feeding 3&5 if the gasket is bad enough, or it/ they are cracked, then you could have a vacuum leak leaning out the cylinders, thus, dry plugs, and no power.

Good luck-

Eric

btw, if you see a teal '91 in the middle of a paint job around town, thats me!

 

ok not a tpi guy and from what you have said i would switch the injector plugs on 3&5 and see what happens. i mean from what i understand about fuel injection is that fuel and spark work together in a certain sequence. you may have already checked this and i didn't see it in your post but that would explain the dry plugs because the fuel coming in gets blown out the exhaust before the plug fires.

if this doesn't help sorry and good luck in finding the problem

 

When people say "3 things are needed" they're making assumptions about what is actually needed, which is:
Air; this is the only one that can be assumed to be present.
Fuel; good fuel to be exact.
Spark; A spark across a tester may not fire under cylinder mixture and compression.
Correct timing; not just timing.
Compression; minimum 80psi.

Fixer's suggestion above is the one I would try first.
If all 8 injectors are spraying then determine where the fuel is going, more importantly if the adjutant cylinders are taking it in then those cylinders should be running rich. What goes in must come out.

 

Hi, guys figured all this out about a year or so ago.. Had 2 plug wires that were bad..go figure brand new MSD's, thanks for all the responses.

 

Ok, so this was an old post, posting the resolution would have kept us from trying help a year later.
Any Hoo, when you say bad plug wires - bad, exactly how?
You said they are new wires and that everything had been checked, so how did you over look 2 bad wires?
Was this an error of assumption?
It helps to know how and why an assumption is made about a crtical part of the ignition system.

 

Figured the date on the posting and the fact it was 10 or more pages back would've been a clue the problem was solved...but any hoo. They were brand new plug wires so the assumption was they were good, seeing that its extremely rare to get a brand new part thats bad. After testing the plug wires individually we found the 2 on the 2 dead cyclinders weren't producing spark, hence our problem solved. to all those who helped.

 

Too bad no one relies on old school oscilloscopes anymore. A bad plug wire would have shown itself immediately.

Problem with old scopes is getting them to interface with newer ignitions.

I bought an old Heathkit scope off of ebay a few years ago and it was a time saver when I had to diagnose a miss on my Acura Legend. A quick look at the ignition wiring diagram and I had the scope displaying patterns like the old days. The bad plug wire showed up like a sore thumb.

 

An even bigger problem with oscilloscopes is finding a still-fully-functional one at a reasonable price. I keep finding them, but these fools want $1500-$3500 for them.

 

You can find portable Heathkit type ones on ebay for a few hundred bucks, but you're correct. It's a hit-or-miss proposition trying to find one that works. Even when the seller claims it's been tested and works fine.

A lot of them are also missing the cables.