85 720 z24 no power?!?!

[Ermugah]

First off, i have much love for this truck. However i am not a mechanic an i do not know what most of alot of you do. So the advice an any information will be absolutely helpful to me.. Id love to learn an of course fix this issue

 

1985 nissan 720 z24 225k

 

The problem: Has no power. Bad idle. Some oil in the air filter. On a straight highway the max speed i can do is 70-75 mph. On a incline, even if i were to down shift, it just want hold a steady speed. Has a rough idle (carb related from the sounds) an sometimes it will i guess choke out an cut off. At a stop sign (after awhile of driving) ill have to keep in the gast. Some of that may be in the carb but does it explain such lack in power? It really feels like a surge, the throttle reaponse is there, but the sound of it an power is just not the same. Ive had all cylinders checked.. All are nearly the same compression. Spark plugs are fresh. Plug wires are good with good connection to the distributor. ( i did have a cracked distributor, but even before then the problem was still occuring) everything is stock except glasspack exhaust an k&n air filter. Nearly 15000 to 20000 miles ago the timing chain an head gasket were done.

 

I will have to put more detail when i can.. But if anyone can help, i would very much appreciate it. Thx

[datzenmike]

Welcome to Ratsun.

 

What compression? If 80 across all four that would be a problem right there.

 

Things you can do, is check the valve lash, timing. Confirm that both coils are firing.

 

Does the air filter have one or two wing nuts holding it on?

[Ermugah]

@datzenmike: thank you for the welcoming

 

The compression from what my guy said.. All cylinders are 90 or over. Tho it doesnt run that way. Also the truck doesn't smoke or burn excessive oil

 

I assume your talking about those 2 main resistors. they both are firing properly.

 

I have yet to get into the timing but im Definetly heading that direction. The valve lash/ does that mean valve adjustment an clearances? Im trying to declare everything i can before i go into the valves an timing.

 

1 wing nut ? Stock 2 barrel carb.

[datzenmike]

Low compression can be tight valves. If still low after adjustment squirt a few tablespoonfuls of engine oil in and try again. If compression jumps the rings are worn out.  

 

The coils have a wire each going over to the distributor cap.

[Ermugah]

Distributer connections are good.

 

Compression is good. 90+ in all cylinders

 

Checking converter, honeycomb may be stopped up.

[datzenmike]

90 is not 'good' but being even is. Engine will run smooth at least. Compression should be twice that.

 

Check for spark not connections. Both coils must be working.

Check valve clearance. Tight valves lower compression.

[Ermugah]

10-4

 

Both of those 2 coils have spark.

 

My guy told me they were nearly 90 even, close to even.. Not very smooth running tho. he thought nothing of it being in the motor (but im with you). what other symptoms can be checked causing that kind of low compression if any?.. He mentioned the converter. Had it checked at the the muffler shop an its flowing like it should. I will do my OWN compression test an update some more accurate info. Its an old-worn truck, im sure it needs a valve adjusment an rings..

 

This is about to become a do-it-myself project. With youtube, a haynes manuel, an a helping hand, hopefully ill figure it out haha

 

Ill update compression .. An move on to the tear down. Thx again

[datzenmike]

Warm the engine, do compression test then squirt several teaspoons of engine oil in the cylinder. If the compression jumps up then the rings are not sealing because worn out. If the compression does not jump up significantly the valves may not be sealing. They may need adjusting or a good valve job. This is cheaper than a set of rings.

 

A leak down test forces compressed air into a closed cylinder. The rate of air that escapes can be seen as a pressure drop compared to the supply pressure. For example 100 PSI line pressure in and 80 PSI in the cylinder. This would be a 20% loss and not very good. If an intake valve is bad you will hear the air escaping out the carb, if exhaust valve you'll hear it at the tail pipe. Leakage past the rings will be heard at the oil fill hole on the valve cover..

[Doctor510]

10-4

 

Both of those 2 coils have spark.

 

My guy told me they were nearly 90 even, close to even.. Not very smooth running tho. he thought nothing of it being in the motor (but im with you). what other symptoms can be checked causing that kind of low compression if any?.. He mentioned the converter. Had it checked at the the muffler shop an its flowing like it should. I will do my OWN compression test an update some more accurate info. Its an old-worn truck, im sure it needs a valve adjusment an rings..

 

This is about to become a do-it-myself project. With youtube, a haynes manuel, an a helping hand, hopefully ill figure it out haha

 

Ill update compression .. An move on to the tear down. Thx again

 

You are obviously not willing to listen to very good advise.  ADJUST the valves, go back to basics on every thing and never mind what "your guy" told you.  Listen and learn!

[Ermugah]

Doctor, No i am willing to learn an take any advice. The truck is in my hands now. From what ive already learned hear, is the reason its a do-it-myself project from hear on. Much easier to learn an figure it out.. It cant be rocket science right.

 

I will update more accurate info.. Starting with the compression an taking the advice given

 

Thx again mike