1994 J30 Code 51 Problems

[XxWITExX]

this is my first post here after many months of reading the site.
So i bought a 1994 j30 about 7 months ago and about since the second week i got it, its had significant acceleration issues and a very slow and rough idle, along with several other issues. at first when i pulled the trouble codes from the obd1 i got the knock sensor code and about 2 weeks ago i got around to putting a new sensor in (relocated it too). well it made it a little better, along with cleaning the MAF and spark plugs. but i still have a poor idle and poor acceleration (just not as bad). after i changed the sensor i started getting code 51. and now im stuck. i pulled all my spark plugs today and they were not fouled in the least bit, except my driver side front 2 spark plugs had a bit of "wet" to them which i was told meant the particular cylinder is running slightly rich. i havent ohm metered the FI yet but the spark plugs would be fouled (i assume) if the fuel injectors were bad(i replaced the spark plugs with platinum tips the day i bought it). so what do you suggest guys? am i wrong or am i missing something? also it appears that one of the preivous owners replaced the foreward passenger side fuel injector (its much cleaner and less grimey than the others and the shielding was cut off the harness for some reason). Thanks guys

[XxWITExX]

Okay so today i went through the EC section of the FSM and did almost every single diagnostic and worked my way into finding out that the 2 cylinders(2&4) that had fluid on the plugs are not firing (i can remove the coil wire while the car is on and nothing changes where as on cylinders 1, 3, 5, & 6 all will make the engine begin to die (which to me means cylinders 2&4 are misfiring. the coils/harnesses are all good and the spark plugs spark when grounded to the plenum.(which confuses me as to why it doesnt ignite). the only thing i could find that was acting weird was my PTU. where it should have had full continuity most of the different combinations of leads for its diagnostic ended up being about 600-700 ohms but that was on all cylinders not just 2 and 4. what confuses me is A. how is my car running on only 4 cylinders B. if it is the ptu why is it that only 2 cylinders are misfiring. side note i didnt really get around to checking the ohms on the FI's. also SIDENOTE i AM running my car (and have been since i changed the plugs apparently) on Autolite Double Platinums, not NGk

[yodawill2000]

If you have the Old style PTU I would start there.
If you search around you will find pics of the Old and new PTU's.
The old one's are known to drop cylinders.
And non NGK platinum's are well known to cause issues in the VG30DE.

[fourdrinie]

if those two fixes dont solve the problem, look for another ECU

[XxWITExX]

the new PTU has 7 terminals on one side and 6 on the other right? where as the old ones were 6 and 6? im fairly positive it is one of the new PTUs. also ive scoured this website trying to find SPECIFIC problems using non ngk plugs can cause or why non ngk plugs dont work. (to me a spark plug is a spark plug)

[fourdrinie]

Wish I could explain the difference, but these Japanese engines run best on OEM NGK plugs!

[XxWITExX]

well i dont think its my spark plugs because its only 2 cylinders that are misfiring. and i can switch the coils/plugs around all day and its still always cylinder 2 and 4 misfiring no matter the combination.

[fourdrinie]

I know the FSM details a continuity test between PTU terminals and ECU pins...check that out! Could be either PTU or ECU

[driverdriver]

XxWITExX

Unfortunately when we migrated to the current forum software, we lost a whack of old archived threads. Using non NGK plugs has produced everything from no start, rough idle and acceleration issues over the last 14-15 years, I've been active on this board (and the previous Yahoo group).

[J30tChumpCar]

Ohm the suspect injectors as well as do a compression test.