LT5 Misfiring at All Speeds

[Johnny5]

Originally Posted by Paul Workman

Food for thought...

After I first got my Z, it had a slight "miss" on one cylinder that wasn't so apparent under heavier throttle - if much at all. Turned out to be a burnt valve, stemming from a weak primary injector!

Just sayin.....

Hey Paul it turns out it was just my plugs, but what did you do to fix your valves. Were you able to buy a single valve? did you have to buy a whole head? and where could you even purchase valves or a head?

[Johnny5]

Originally Posted by Big D

Ok everyone, Got the plenum off with no problem. Way easier then what I had imagined with all the good info on the Registry. Took about 40 minutes and broke nothing. However, I tried a suggested method for anti-freeze removal, just drain the plenum, and I would not advise that method. After releasing the plenum, antifreeze began bubbling up from the two holes in the injector housing. Plugged the holes quickly and then drained the radiator. Saving ten minutes at first cost me hours in cleanup. Dang, I hate antifreeze. The valley was extremely clean, prior to the antifreeze dump and all connectors and hoses are in very good shape. Well, at least I know the valley drain works just fine.Tested the wires and they come in at 7.5-9 K ohms for all, well within spec. Also checked the coils, all 4 coil resistance within spec. Also did a visual of the coils and they all look good, no signs of heat deterioration or cracking so I am going to let them go and just change out the injectors. I may end up regretting this decision but I was going to go with stock coils anyway so I don't see the advantage at this point. This is a very low mileage car. Looking forward to installing the new FIC injectors and getting her back on the road.

Big D
69 L46, M21
90 ZR1
95 Suzuki 1200 Bandit
2014 Triumph Thruxton

Working with Jim Wazoo Leader he had a coolant suction tool. It is very useful. His hooks up to an air compressor which is cool but I don't have room in the garage for that if I pull the plenum with the car in there so I bought the same thing but it is a manual pump and you can reverse it and put the coolant back in. Pretty neat and handy for plenum pulls. I bought mine for $80.

https://www.google.com/shopping/prod...acF8WzeuH_logC

[Big D]

Originally Posted by Johnny5

my father changed the back 2 plugs the other day and it runs great now. Not a damn problem.....except my bose radio lol Did you ever find out why your lt5 is missing? I am curious

Nope, still chasing it. Haven't had a chance to get back to it because the Blazer decided it liked to shift into 4WD all by itself so I've been playing with that with my free time. Looks like a TCCM problem.

Still is pointing to the ECM with the big difference in resistance between #6 and the other 7 pins into the ECM. Not yet willing to shell out the $300 or more to experiment.

[Johnny5]

Originally Posted by Big D

Nope, still chasing it. Haven't had a chance to get back to it because the Blazer decided it liked to shift into 4WD all by itself so I've been playing with that with my free time. Looks like a TCCM problem.

Still is pointing to the ECM with the big difference in resistance between #6 and the other 7 pins into the ECM. Not yet willing to shell out the $300 or more to experiment.

My father owned a 96 jimmy and a 2000 jimmy and did all his work himself. PM me with your number and im sure he could point you in the right direction

[A26B]

Originally Posted by Johnny5

Hey Paul it turns out it was just my plugs, but what did you do to fix your valves. Were you able to buy a single valve? did you have to buy a whole head? and where could you even purchase valves or a head?

Pay us a visit & see what we have.
www.jerrysgaskets.com

[Paul Workman]

Originally Posted by Johnny5

Hey Paul it turns out it was just my plugs, but what did you do to fix your valves. Were you able to buy a single valve? did you have to buy a whole head? and where could you even purchase valves or a head?

Replacing a valve in an LT5 requires the motor to be pulled to facilitate the cam phasing, etc., after the valve(s) are serviced/replaced. So, I opted to complete my porting at that time as well.

As it happens, I had a porting mishap resulting in replacing one head out of convenience; a "do-over", if you will.