Miss fire on cly 4, 73 d-jet Options

[rfinegan]

I have been narrowing down the Root Cause on a misfire 73 2.0 D jet. Cold it hits on all 4 but as it warms up I have a miss. Compression a little low but may be washed down rings. 10% leak down/ seem to seal up ok.

When I disconnect the injector no change. Plug back in no change
Noid light check for pulse PASS
Spark getting to the plug PASS. Change plug anyhow as it was new and unknown state

Gut tells me I have an injector acting odd

Today I ran the same basic test: I had a good idle but fast, 1300-1500. Figured I has hitting on 4 now...I pulled the wire off the injector and the speed went UP.. plugged back in and the speed went back down. WTF

NEXT STEP:
1) add fuel gage and confirm pressure ; adjust regulator as needed ( fuel Line kink has been fixed (was lean) pressure base line unknown
2) swap injectors 3/4 see if problem follows to Cly 3. (best)
Or put a different injector in Cyl 4 and test for new behavior (lazy)

Other: I borrowed my 123 Distribute and installed in the 73 2.0 to base line an ignition problem (jumping Tach) Root Cause was a Coil installed backwards.
Smoke machine test shows no Vacuum leaks. Ever so slight leak at throttle shaft, but feels great

Curious as to see if others feel that injector is off in the weeds? Sticking and now leaking?

[Lockwodo]

You may be right about the problem being related to a dodgy injector and to get at that I prefer the "best" approach.

Is the distributor stock? I wonder if shaft looseness or trigger point issues could contribute to misfires? If you still have the 123 disty you could try swapping that back in and see if the misfire issue goes away.

[emerygt350]

Strange stuff indeed. Maybe swap injector with another cylinder? If the problem moves you know you have it figured out.

[rfinegan]

YES, The 123 is in right now and clean things up to let me find the #4 dropping out.
I have a set of 4 spare injectors but state unknown. I also have my running 75 Djet I have been pulling test parts from for diagnostics. Its on stand getting new SS fuel lines so it only my time..low/no cost

Thanks for the feedback, I will have some details soon

You may be right about the problem being related to a dodgy injector and to get at that I prefer the "best" approach.

Is the distributor stock? I wonder if shaft looseness or trigger point issues could contribute to misfires? If you still have the 123 disty you could try swapping that back in and see if the misfire issue goes away.

[rfinegan]

Also the MPS is rebuilt from a 73 djet at auto Atlanta and new resister shunt inline from the temp sensor too (73 only)

[rfinegan]

update
I did stick to the plan and with swapping the 3/4 injectors. I did induce another variable by using injector cleaner and flushing and comparing the spray patterns with an injector pulser and a mock flow bench / fuel pump. This now hits on all cylinders and miss fire is gone..For now..we will see, and send them off to Mr injector if any issue persist

[Lockwodo]

update
I did stick to the plan and with swapping the 3/4 injectors. I did induce another variable by using injector cleaner and flushing and comparing the spray patterns with an injector pulser and a mock flow bench / fuel pump. This now hits on all cylinders and miss fire is gone..For now..we will see, and send them off to Mr injector if any issue persist

(IMG:style_emoticons/default/beerchug.gif)

[rfinegan]

Cleaned injector is still running like a champ...Customer says its the best its ever ran since he has owned it! Woo hoo

[Ron914]

I used Mr Injector to test and clean my original Bosch green injectors to like new . He did a great job and was cheaper than replacing with the FJ67 injectors. $88.00 plus $9.50 shipping