Interesting compression test in my old truck

[85 Cutlass Brougham]

Another update: Just got back from my local Nissan dealership. I bought a new EGR valve gasket, oil pump gasket and drain plug seal for $5.81 and will see if I can fix the problem as soon as the engine cools down. I figured that while I was at it I would try to fix the annoying 1qt/3k-4k mi oil consumption the truck has. I had it down to 1/2 qt but then the pump and plug started leaking a little so I hope this helps. I hate a oily, greasy engine and undercarriage. Once I get these replaced along with the steering gear seals, I will probably have to degrease the underside of the truck again...

 

[85 Cutlass Brougham]

Still runs like crap even after cleaning out all of the passages and the EGR valve. I even put another set of plugs in it and no improvement. At least is seems to run well off idle, but I honestly haven't done more than drive it once up and down my street.

 

[megaladon6]

I adjusted the throttle body's cold idle circuit

exactly what did you do? the throttle body shouldn't have a cold idle ckt. the ECM uses the IAC and injection timing to adjust for cold air/engine. the screw that looks like an idle set screw should never be touched.
if possible set the "cold idle ckt back to where it was, completely clear the computer. all the fuel trim values and solenoid positions need to be reset in the memory. then start the engine and let it idle until it's warmed up. then drive it at varying speeds between 30 and 45 for half an hour them 50-65 for 1/2 an hour. this is a generic drive cycle to reset the monitors and trim values. the start up needs to be done on a cold engine, preferably after a full 8 hours sitting.
sometimes the fuel values will take a long time to change on their own after a fix. look at jeeps after a battery change, they sometimes need 2 dozen starts to stay running.

 

[85 Cutlass Brougham]

Frontier's are quirky in this regard. They use what Nissan calls a "Thermal Unit" which operates like a thermostat, with a wax pellet that shrinks and grows with temperature. It has a set screw that is adjustable on top of it. This adjusts the position of a cam. A roller rides on the cam that is attached to the bell crank for the throttle. This in turn is adjustable for position with another screw which allows you to align the roller with the 2 marks on the cam which allows you to set the cold and hot idle speed. Finite idle adjustments are in turn also adjusted with the IAC motor. Base idle speed is adjustable with a plastic base idle speed screw (Same as a BISS screw on a Mitsu 4G63) which is an air bleed. I am using the correct FSM from Nissan for a model year 1998 Frontier to guide me in my diagnostics. If I could, I would also be using the Nissan Consult II scanner to further help me in my diagnostics, but I can't find one cheaply ( But I can find a Consult I replica for $150--go figure...). I have a basic OBD II code scanner which tells me what is wrong and lets me turn off the CEL, but that's about it. Yes, I know what I just described about the throttle body sounds crazy but get a copy of the FSM out and read it and you will see that I am not nuts!

I also opened another can of worms trying to adjust the TPS and now it revs to the moon with the IAC connected, so I unplugged it. It still idles OK, but throws a code P0505 (no IAC signal) which is expected, and yes, I still have the P0303 too... So, I unfortunately am scheduled to be off on Thurs. and I will be messing with it all over again then. I work 4pm to midnight tomorrow and have school at 8:30am, so I need to just leave it alone for now.

 

[megaladon6]

in that case just pull the battery for 30min. that'll clear everything. you can't adjust things unless the fuel trims are correct otherwise you copound problems.

 

[85 Cutlass Brougham]

Thanks. I will try that Thursday.My day is packed from when I get up at 7:45 am till around 11:30-midnight tomorrow so I have no time now.

 

[85 Cutlass Brougham]

I finally fixed the misfire! It used to misfire a little bit, but had gotten worse after I had fixed another problem back in June. One of the things I had done then was to remove and clean injector #3 as it was not firing at all at that time. I did finally get the engine to run, but was worse than it was before #3 had quit all together. So, I pulled an injector from a 97 Nissan D21 pickup for $9.99 at the U pull it and swapped it into my Frontier (D22). No misfire anywhere now! It runs like a new truck. I think the combination of cleaning out the EGR passages and repairing whatever I had done before ( I found a nicked bottom O ring on the old injector which was probably the real problem) has finally made it run like a good vehicle again. Thanks to everyone who gave input on this matter.