My 98 Balzer LS 4 door 4x4 is misfiring a lot in cylinder 4 & 5. When the engine is cold you can definately feel it when driving (head is bouncing back and forth). After it warms up it seems to go away or hides it self better. I replaced the plugs, wires cap and rotor about 6 months ago and I thought it helped but it could have been better from the warm summer months. Recently I had a mechanic hook up a scanner. It difinately showed that 4 & 5 had multiple misfires. He thought the injectors may have sticky poppets. So I did some research and found that they had trouble with them so I put in the updated injector system(csfi to mfi) used on newer models (recommended on GM service bulletin). Well that didn't fix it either, runs the same. The fuel pressure is questionable. I am running at 55psi. Is that to low? Is that acceptable for the updated injector system(MFI). The pressure is consistantly at 55 wheather the engine is cold or hot, so I had my doubts with that and only 4 & 5 are getting picked on. I don't know what to do next. Please advise.

Fuel pressure should be 60-66psi with the key to the first position.

I'm at 55psi with key on engine not running. So is my pressure, without a doubt, unacceptable? Is this going to cause the two cylinders to miss and get better when the engine heats up. I just don't want to replace a $400 part unless I know for sure that is it.

Thanks

My 98 Balzer LS 4 door 4x4 is misfiring a lot in cylinder 4 & 5. When the engine is cold you can definately feel it when driving (head is bouncing back and forth). After it warms up it seems to go away or hides it self better. I replaced the plugs, wires cap and rotor about 6 months ago and I thought it helped but it could have been better from the warm summer months. Recently I had a mechanic hook up a scanner. It difinately showed that 4 & 5 had multiple misfires. He thought the injectors may have sticky poppets. So I did some research and found that they had trouble with them so I put in the updated injector system(csfi to mfi) used on newer models (recommended on GM service bulletin).

I would assume the mfi upgrade would have done the Fuel Pressure regulator (another problem point - I am just about to do a Fuel Pressure regulator swap this weekend on mine). Interesting point about the csfi to mfi upgrade, didn't know that was possible.

Well that didn't fix it either, runs the same. The fuel pressure is questionable. I am running at 55psi. Is that to low? Is that acceptable for the updated injector system(MFI). The pressure is consistantly at 55 wheather the engine is cold or hot, so I had my doubts with that and only 4 & 5 are getting picked on. I don't know what to do next. Please advise.

I can only speak for CSFI, but minimum of 54 PSI is acceptable for idle operation. While driving around on the flats, I am seeing around 56 psi, uphill I can see around 58-60 PSI. Even giving the engine a little gas at idle should show a pressure spike.

Cyl 4 & 5 missfires.. Hmmm.... Hate to state the obvious, but could it be dirty injectors? I would start with lots & lots of injector cleaner, if you haven't done that already.

Next most obvious thing, check the sparkplug gaps on Cyl 4 and 5. Check for loose connections at the spark plugs and distributor. If you really want to go gung ho, try checking the sparkplug wire resistance. I am seeing about 1Kohm on mine (but they ain't the normal wires).

The only other thing would be valve seals.. YUK! Compression tests on the cylinders wouldn't be bad either. I seem to recall that there 'could be some way of doing the compression test to determine if you are having Valve/Ring issues.

Regards,
---- Robb -----

I'm at 55psi with key on engine not running. So is my pressure, without a doubt, unacceptable? Is this going to cause the two cylinders to miss and get better when the engine heats up. I just don't want to replace a $400 part unless I know for sure that is it.

Thanks

Yes, your pressure is too low.

Suggest changing the fuel filter first.

Brand spankin new injectors. It did it again immediaelty after I installed them. Still picking on 4 and 5 for some reason. I do get the spikes to 60 psi when I rev it some. I will probably start over and check the plugs, wires and all that. I suppose a compression check is a idea too. The regulator comes with the injectors also. Actually it is cheaper to install the mfi than it is csfi. If any one is interested call Banks Chev in N.H. I bought the injector kit , mounting bracket and seal kit for $200. That's $175 less than my local dealer. Too bad it didn't fix it though.

Regards

I forgot to mention, the filter is brand new also. I suppose that means the pump would be next, right?

Regards

I forgot to mention, the filter is brand new also. I suppose that means the pump would be next, right?

Regards

Fuel pressure regulator could be causing it.

Is that the little diaphram thing with a short tube on it and it's mounted to the fuel injector housing? If so, that came with the new injectors.

Have you looked at your distributor module or your coil? What about the ignition module? That's about the only think left for spark...

With it only missing on 4 and 5, I wouldn't think it would be a coil. I should put it on a scope just in case the misfires are from an ignition problem. Where does the signal to fire the injectors come from? Does that come out of the computer. Maybe there is a driver output failure for the injectors. I may hook up an oscilloscope on the injectors to see if they are pulsing (if that's how they operate). Does any one have a link to an electrical schematic for ingnitions and fuel injectors? Computer too?

Brand spankin new injectors. It did it again immediaelty after I installed them. Still picking on 4 and 5 for some reason. I do get the spikes to 60 psi when I rev it some. I will probably start over and check the plugs, wires and all that. I suppose a compression check is a idea too. The regulator comes with the injectors also. Actually it is cheaper to install the mfi than it is csfi. If any one is interested call Banks Chev in N.H. I bought the injector kit , mounting bracket and seal kit for $200. That's $175 less than my local dealer. Too bad it didn't fix it though.
Regards

Boy, I would have liked to have heard about that. I just did a fuel pressure regulator swap (cost: $55.00 US ), but would have done the MFI upgrade had I of known. GM dealer here charges around $550.00 ( US ) for the part.

The way the fuel pressure is spozed to work is like this (according to alldata)

Turn the key: Fuel pump kicks in for 10-15 secs.
You should see around 60-66 PSI while the pump is running.
You should see around 54-60 PSI while the pump is off.

Mine drops to 54-60 PSI quite quickly, but holds to this pressure afterwards. Others say the pressure should hold at 60 PSI. On mine with the brand new pressure regulator I am simply not seeing this.

Once I start the engine, at idle, I am seeing 54 PSI. When I gun the engine, I can see the pressure spike up to around 60 PSI. So in that regard I think your fine. I therefore do not see your problem being a fuel pump / fuel pressure issue.

Missfires on Cylinder #4, #5...
-New wires / Spark Plugs.
-New MFI injection.
-New Fuel Pressure Regulator.
-New Fuel Filter.

That doesn't leave you alot of options....

#1 Clogged/dirty injectors
- Lots and lots of injector cleaner for the next few fills (*Cheapest*)
- Maybe a professional injector clean at a shop?

#2 Bad valve seals / rings.
- Compression testing.
- Spending lots of $$$.

Regards,
----- Robb -----

With it only missing on 4 and 5, I wouldn't think it would be a coil. I should put it on a scope just in case the misfires are from an ignition problem. Where does the signal to fire the injectors come from? Does that come out of the computer. Maybe there is a driver output failure for the injectors. I may hook up an oscilloscope on the injectors to see if they are pulsing (if that's how they operate). Does any one have a link to an electrical schematic for ingnitions and fuel injectors? Computer too?

What I did to check mine (you're not gonna like this) is I took the upper manifold apart leaving the MFI ( CSFI in my case ) still in place. I re-connected all the electrical sensors, disabled my ignition coil (note: the coil *WILL* arc if it is left active, open fuel on the top of the engine, getting together with that coil arc would be BAD i think! Simply pulling the wire off the coil on mine causes the arc to shoot out the top, and back down to the coil case - SCARY STUFF - Pulling the wire will not cut the mustard here). I then simply pulled the poppet valves of 'interest'. Cranking the engine I could see the fuel 'spurting' out the poppet.

If you want to try it 'electically', I *SUSPECT* that the big electrical plug that your plugging into the MFI is simply 6 solenoids. You'll see 2 wires per solenoid. Pulsing energy into the solenoid causes fuel to pulse out the poppets into the cylinder.

Are you seeing the check engine light, and getting the error codes indicating missfires?


Regards,
---- Robb ----

I am getting the engine light and the scanner reads several misfires in 4 and 5. I keep hearing I should run injector cleaner. I just can't believe that with brand new injectors and filter I am still getting misfires on the same two cylinders. I think compression testing and testing the injector pulses and putting it on a scope to check the firing in the cylinders should give me some answer. Thanks for all the advise. I'll still keep checking this forum for more advise and I'll post the fix when I figure it out, as I'm sure all of you would like to hear about.

Regards

I am getting the engine light and the scanner reads several misfires in 4 and 5. I keep hearing I should run injector cleaner. I just can't believe that with brand new injectors and filter I am still getting misfires on the same two cylinders. I think compression testing and testing the injector pulses and putting it on a scope to check the firing in the cylinders should give me some answer. Thanks for all the advise. I'll still keep checking this forum for more advise and I'll post the fix when I figure it out, as I'm sure all of you would like to hear about.

Regards

I would recheck your cap and rotor.

Well, I think I have it fixed. The compression tested good. I hooked an electronics oscilloscope to the injectors, they looked good. Then I hooked up an automotive scope to the plug wires. It didn't look real bad, but I think that's because I didn't put it under load (that's when it misfired the most). After that I started testing resistance on the plug wires. #4 had 800k ohms, #5 had 250k ohms, the coil wire had 50k ohms, there was another bad one and the rest where good (around 1k ohms). I wouldn't have thought six month old wires would fail that fast. I returned them and got replacements for free. They are Autolite Premium wires. I'm not sure if Autolite makes a good wire or not. I tested them before installing and they all had around 1k ohms. Thanks again guys, it's been educational.

Well, I think I have it fixed. The compression tested good. I hooked an electronics oscilloscope to the injectors, they looked good. Then I hooked up an automotive scope to the plug wires. It didn't look real bad, but I think that's because I didn't put it under load (that's when it misfired the most). After that I started testing resistance on the plug wires. #4 had 800k ohms, #5 had 250k ohms, the coil wire had 50k ohms, there was another bad one and the rest where good (around 1k ohms). I wouldn't have thought six month old wires would fail that fast. I returned them and got replacements for free. They are Autolite Premium wires. I'm not sure if Autolite makes a good wire or not. I tested them before installing and they all had around 1k ohms. Thanks again guys, it's been educational.

I just installed Autolite Pro-fit wires myself.

We'll see how they perform and stand up.

So I did some research and found that they had trouble with them so I put in the updated injector system(csfi to mfi) used on newer models (recommended on GM service bulletin).

Could you please provide me with the numbers and website of where you got your injection system. A CSFI to MFI upgrade is sounding pretty darn interesting to me right about now. I tried to locate banks chev on the net with no real success, so providing some contact info would be great.

Thanks....

----- Robb -----