Where to start diagnosing power loss/startup problem - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
User Tag List

 
LinkBack Thread Tools
post #1 of 4 (permalink) Old 04-19-2019, 07:34 PM Thread Starter
Junior Member
 
pantz's Avatar
 
Join Date: Apr 2019
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
(Thread Starter)
Where to start diagnosing power loss/startup problem

Hey all,

I have a 1978 Datsun 280z and am having some trouble figuring out where to start diagnosing its first engine issue. Got the car about a month ago and it started and drove just fine. A few days in I drove it a little hard and it suddenly started stuttering and hesitating around 2500 - 3000 RPMs. Took it home and it was idling at around 500 with a bit of white/grey smoke coming out of the exhaust. The level of exhaust smoke is increased when pressing the accelerator.

I thought maybe I had blow a head gasket, however, during the next week I did a chemical test which showed negative for exhaust fumes coming through the radiator. Let it sit for a bit longer (not a lot of time to tinker because of work), still running at around 500 with a small amount of smoke through the exhaust. I then did a compression test which showed 130 psi across all cylinders. Note that the spark plugs are black so I suspect it's running very rich.

That leads to this week when I was planning to do a wet compression test to rule out worn piston rings. Start engine and the idle is down to 250. Give car a bit of gas, and car stalls and refuses to start up again.

So now I'm stuck and wondering where to continue with diagnosing this problem. Maybe it's a busted fuel pump, or a major vacuum leak? Timing? I am planning on doing a leakdown test tomorrow to see if air is escaping somewhere and then checking the fuel pump but after that I'm a bit rudderless.

Any tips you guys have would be immensely appreciated!!
pantz is offline  
Sponsored Links
Advertisement
 
post #2 of 4 (permalink) Old 04-20-2019, 10:36 PM Thread Starter
Junior Member
 
pantz's Avatar
 
Join Date: Apr 2019
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
(Thread Starter)
So, instead of the leakdown test I went and printed out the EF portion of the FSM. Went through all of the continuity tests for engine not starting and it failed on AFM and water temp sensor. Going to test those further tomorrow and see what's going on there.

Last edited by pantz; 04-20-2019 at 10:39 PM.
pantz is offline  
post #3 of 4 (permalink) Old 04-21-2019, 12:28 AM
Senior Member
 
Join Date: Jun 2016
Posts: 512
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 107 Post(s)
Glad to hear some culprits have been found. While you are wrenching, take care of the vacuum leaks too.

1978 280z - stock L28 engine - Dallas, TX
chaseincats is offline  
Sponsored Links
Advertisement
 
post #4 of 4 (permalink) Old 04-21-2019, 11:41 PM Thread Starter
Junior Member
 
pantz's Avatar
 
Join Date: Apr 2019
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
(Thread Starter)
Alright, I took some readings off of the AFM. Everything tested fine EXCEPT for the air temp sensor. With three separate readings at ~68F degrees outside the resistance ranged between 67 and 80 kohms. The FSM states that the correct range is supposed to be between 2.25 and 2.75 kohms, heh.

Has anyone had experience with faulty AFMs? It's a relatively expensive part so I wanted to know if others have encountered this as well. FSM recommends replacing the entire assembly but it would be a shame to do that if only one piece is busted.

Second thing that I did was check the water temp sensor. This, unfortunately, needs to be replaced too. I took it out of the engine and tested it in room temp and boiling water. At ~68F the resistance was fine but once it got to ~175 it was about twice as high as the FSM states it should be. I'll be ordering a new one of those tonight.

BONUS - check out the AFM to throttle body boot:



Looks like one of the previous owners wrapped the end with electrical tape and slapped it back on there. Going to order a replacement immediately!
pantz is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



  Similar Threads
Thread Thread Starter Forum Replies Last Post
280zxt need help diagnosing problem. mkgtn 70-83 Tech Discussion Forum 18 03-06-2009 05:42 PM
Diagnosing last known problem!! 93sport500z 90-96 Tech Discussion Forum 1 10-29-2008 07:54 PM
At a loss concerning power loss Z06C5R 70-83 Tech Discussion Forum 10 04-28-2006 01:06 PM
need help diagnosing problem - distrubitor - idel - carbs? 24ounce 70-83 Tech Discussion Forum 4 02-24-2005 02:17 PM
help diagnosing starting problem 2CLASSZ 90-96 Tech Discussion Forum 4 11-06-2002 01:41 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome
 


Content Relevant URLs by vBSEO 3.6.1