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Gary
Gary, ASE Certified Technician
Category: Chevy
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Experience:  Senior Technician
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I also have a 1990 or so 350 I rebuilt, rings, bearings, did

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I also have a 1990 or so 350 I rebuilt, rings, bearings, did the heads, new lifters, it has a dual plane manifold with a new Edelbrock 1404 3204 carb, it also does not fire on numbers 5 and 8, I have checked firing order many times, checked the wires ( all good ) plugs good, I did check the intake runner, it is feeding numbers 5 and 8 from the rear barrel on passenger side, at idle isn't only the front barrels supplying fuel ?
JA: Has the vehicle turned into a gas hog? And how does it start -- same as usual?
Customer: stars and idles fine, just when you remove the plug wires do you notice it not firing on 5 and 8 at all
JA: What is the model of your '90 Chevy?
Customer: Oh, it was in a 1990 C-1500 truck, it is now in my 1988 Jeep Wrangler with a 700 R4 auto trans
JA: Are you fixing your Wrangler yourself? What have you tried so far?
Customer: Timing, new plugs, timing light on all wires so I know I'm getting spark at the plugs,
JA: Anything else you want the mechanic to know before I connect you?
Customer: Just don't seem to be getting fuel to these 2 cylinders for some reason, should I by a single plane manifold

Hello! My name is Gary.
Welcome to JustAnswer.
I'm reviewing your question now, and will post back with a reply shortly.

Hello there,

What is the firing order you are using?

If it only these two cylinders then it, will not be a carb or manifold issue.

Either the plugs are faulty, (measure with an ohmmeter, seen this many times), or the valves are too tight.

How much lifter preload did you set at?

Gary

Customer: replied 2 months ago.
18436572 firing order, just tightened lifters so I could still twist the pushrod

Have you done a compression test as yet?

The spark is firing from each plug lead to ground when you remove it from the spark plug?

Is the camshaft made for this firing order?

Gary

Customer: replied 2 months ago.
Will do compression tomorrow, it's the original camshaft, valves all have plenty of movement, do you want me to pull wire off the plug and ground to the head ?

I want you to verify the No. 5 and No. 8 leads are sparking to ground, if these are the cylinders that are misfiring.

Your Edelbrock is a 500, a little small for me, but they still run good out of the box.

Are all the lifters quiet now?

Gary

Customer: replied 2 months ago.
I got the carb from a guy that was going to put it on a v6, I got it cheap, but I think my 350 is probably only about 220 hp anyway, lifters are quiet

Ok, let's see you do have spark from the 5 and 8 leads, and the compression test results.

The 500 will be fine to 5000 rpm or so, perfect for stock street car.

Gary

Customer: replied 2 months ago.
OK will do tomorrow

Ok, good luck for tomorrow.

Gary

With your intake manifold, cylinders 1,4,6 and 7 are fed from one half of the carb.

The other half, primary and secondary feeds 2,3, 5 and 8.

How have gone with some further testing?

Gary

Customer: replied 2 months ago.
Will be doing testing in another 1.5 hours

There first thing I would do is check the resistance of those two plug leads.

Even a new lead could be open circuit.

Do you have a digital multimeter?

If they test ok, then move on to compression test.

I'll hear from you when you know some results.

Gary

Customer: replied 2 months ago.
I do have a digital multi meter, how do I test the wires, ( I did by a inexpensive set of wires when I put this engine together )

Ok, take off one at a time, so you don't get lost.

Set your meter to 20k ohms, and put the meter leads together. Meter should read zero.

Probe each end of a good known lead, meter should read about 5k ohms, 5000 ohms.

Hopefully no 5 and no 8 give an open reading.

Some leads are as low as 50 ohms per foot.

Gary

Customer: replied 2 months ago.
What is an open reading ? 0

An open reading would be whatever you meter says while disconnected.

While the meter leads are shorted together, the meter should read zero.

Gary

Customer: replied 2 months ago.
ok
Customer: replied 2 months ago.
All wires have readings, 1.6 or so for a long one, .60 for a short one, but all have readings, moving on to the compression test
Customer: replied 2 months ago.
Hi Gary, compression test cold engine ( I already had the plugs out ) 1= 135, 2= 140, 3= 130, 4=155, 5= 130, 6=135, 7=130, 8=130

That all seems fairly normal.

Can you read the spark plug from the terminal to the centre electrode?

And do no. 5 and 8 look different to the rest?

Customer: replied 2 months ago.
Number 5 is white, the rest are dark, not sure what you mean by reading the spark plug from the terminal to the center electrode

Ok, with your meter the plug should either read zero ohms or about 4.5k ohms for a resistor plug. From the terminal end to the centre electrode.

The no. 5 being white certainly sounds lean.

I would say you have no fuel entering the cylinder, it can still generate a compression reading, so please don't be mislead by this.

If you are quite sure it is only these two cylinders 5 and 8, then is there any chance of some abnormality in the intake manifold for that runner?

Or possibly the inlet lobes have been wiped off the cam?

Can you run the engine with the valve covers off to check the valve operation?

Gary

Customer: replied 2 months ago.
Definitely 5 and 8 are not firing, I remove the plug wire with engine running and no difference in engine rpm, I can run the engine with valve cover off and it looks like all valves have same movement, I did buy this manifold used on Ebay, do I need to remove it for some inspection ?
Customer: replied 2 months ago.
This engine was a throttle body engine, I got rid of that for a carb so I could eliminate the computer

This is certainly an interesting issue.

If you have spark from both 5 and 8 wires to ground, the valves appear to be working, then pull the carb and see if there is a lump of wood in the runner?

Something stopping airflow from the carb into those 2 cylinders.

Or have you got a power brake hose plumbed to that runner?

Is the carb a bit lean maybe?

Gary

Customer: replied 2 months ago.
Power brake goes direct to back of carb, carb is out of the box new, should be factory set, I will remove carb and look in runner

Ok while you have carb off, I would verify the float levels are correct.

I have yet to see any carburetor that I have used, Edelbrock, Carter, Holley, BG, QFT, etc be correct out of the box.

The floats take a beating with no fuel in the bowls.

Gary

Customer: replied 2 months ago.
I will try to check the float levels, I have the booklet that came with the carb, it may have section on carb adjustments.

The edelbrock is a good carb, and the owners manual is a good tuning aid.

The inlet manifold you have on there could have some fault and that's why the seller sold it on ebay?

Gary

Customer: replied 2 months ago.
Could be

Come back when you have the carb off the manifold.

Hopefully something stands out.

Gary

Customer: replied 2 months ago.
Will do

Just another thought, did you have the intake manifold surface ground to match the angle of your heads?

You could have a vacuum leak across the gaskets?

How far out from seated are the mixture screws?

Did you have the throttle wide open while you did the compression test?

Are all the valve heights still the same when each valve is shut?

I've had one engine with a valve not seating, still had 160 psi, but misfiring.

Gary

Gary

Customer: replied 2 months ago.
I just mounted the manifold, didn't do any machine work, I had to slot the bolt holes on the manifold on the center of the manifold to fit the center bolts as they go in straight down as opposed to the others that go with the angle of the manifold to head
Customer: replied 2 months ago.
Carb was closed on comp test
Customer: replied 2 months ago.
Idle screws are 3/4 turn open from full closed
Customer: replied 2 months ago.
Valves all look the same

Nothing odd as yet?

Have you retorqued the intake manifold?

Customer: replied 2 months ago.
Maybe I should redo the intake gasket altogether, I did notice about a teaspoon of green coolant water in the way back corner of the intake manifold down in a low spot, not sure where that came from.

Yes, sounds like you have found something now.

V8 engines are prone to leaks of different types.

Good luck on the next step, I feel your pain.

I use a bead of sealant along the block rails, no gaskets.

Only gaskets on the intake side of the heads.

Gary

Customer: replied 2 months ago.
any sealant needed on the head and intake or just the ends

I use a tiny bead around the water ports only.

Prior to running the rail beads, I already know the necessary height from a trial run.

Run the rail beads, fit the intake gaskets with a tiny bead as nec for water only.

Fit the manifold with no moving around etc, get all bolts in, pull down gently in many stages.

Clean up the front and back as necessary, like a bathroom sealant job.

Let set overnight.

Gary

Customer: replied 2 months ago.
Thanks

I'll leave it with you now, and we'll talk in a day or two.

Have a good look over that manifold and the new carb as above.

Gary

Customer: replied 2 months ago.
Will do, thanks Gary

Hi again,

Just another thought.

Would you contemplate changing to a lowrise single plane intake?

I ran one on one of my V8s with an edelbrock 600, went really well from off idle to 6600, even with the cam I had.

Gary

Customer: replied 2 months ago.
I would, I was wondering if a single plane would allow the fuel to be shared better between cylinders.

I would do some measuring to see what room you have under bonnet, then check at your local speed shop to see what is available to fit.

Now that you are taking the manifold off, it is worth an experiment.

I think you will be pleasantly surprised at the performance.

Gary

Customer: replied 2 months ago.
Do you think it will rectify the no fuel to 5 and 8 issue

I would like to think that it would.

As long as we are sure that those two have the 4 stroke cycle happening, and spark.

When you get the manifold off, have a good look at that shared runner, top and bottom etc for vacuum leak etc.

You may find that the other pair at the front are being fed just enough to not misfire.

Does the misfire only occur at idle?

Gary

Customer: replied 2 months ago.
Not sure if the misfire is only at idle, when you rev to about 2000 rpms it gets really smooth, let me set engine to about 2000 rpms and try removing the wires, I was almost wondering if this carb is supposed to do this at idle

Ok, I would richen the idle mixture screws, 3/4 turn out is not enough normally.

Try it at 2000rpm, which will prove either way.

Try it on good cylinders as well for comparison.

Gary

Customer: replied 2 months ago.
ok

Hi again,

I should have asked earlier, what distributor do you have?

And what body is this combo in?

Gary

Customer: replied 2 months ago.
HEI distributer, 1988 jeep wrangler

Ok.

So you don't have a bonnet issue, like a Camaro might have.

Are you happy to stay with the Edelbrock, or would you like to try another carb if you go to a single plane manifold?

Have you got another carb to try now, before you pull the manifold for the coolant weep?

Gary

Customer: replied 2 months ago.
no other carb handy, I would prefer not to buy another carb if I don't have to,
I will try the idle mix screws, they are 3/4 turn open now, I will open another 1/4 at a time and see if it gets 5 and 8 firing.

Ok, I would ensure there are no vacuum leaks.

Then adjust each idle mixture screw slightly richer to the point of highest idle speed.

You should be able to find the happy point, further out should make it slow down from being rich.

You will need to lower the curb idle speed screw a bit as you do this.

Gary

Customer: replied 2 months ago.
got it

It would be great if this is your issue.

Fingers crossed.

Gary

Customer: replied 2 months ago.
Hey, Gary, I opened the idle mixture screws 1/2 turn at a time, by the time I opened them each 2 full turns I got both cylinders back, they are each at 2 3/4 turns open, let me put the rest of the thing back together, still need to hook up the carb to transmission cable and a few adjustments and we will see how it acts under a load

That's sounding like good news for now.

If you now have all 8 cylinders, will you be going for a little drive soon?

How about the little coolant leak?

Gary

Customer: replied 2 months ago.
I can drive after I hook up a few more things, I think I will monitor the coolant level for a bit and see how that goes

That's great, bet you are excited for a small maiden drive.

Hopefully hear from you in a day or two.

Gary

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