Guest 4.3L 280z Posted November 6, 2004 Share Posted November 6, 2004 I've got a 4.3L(same as a 350 minus two cylinders) in my 280z, I got it from a guy who seemed trustworthy. He said the motor had only about 1000 miles on it since rebuild. Now I've got it in the car and I did a compression check. Its increasing during every stroke but only maxing at 60. I've got the distributor in right, I checked for the compression stroke and then put it to 0 degrees and the rotor between 1 and 6 cylinders. It backfires really bad and sometimes slows down after it backfires while turning over, it doesn't sound like its firing right at all! If I move the distributor way off it doesn't backfire so much but no starting. Does this sound like it could be anything but a timing problem? I really hope I didn't get ripped off cause I've already spent a lot of money and 3 or 4 years and I'm not making as much as I was when I started working on it. p.s. I'm assuming the timing chain is installed right beings he said it was running. Quote Link to comment Share on other sites More sharing options...
80LS1T Posted November 6, 2004 Share Posted November 6, 2004 60PSI is deffinetly not ok for a compression test results. That would be ok for a running compression but not for an enginen that is not running. I would make sure the timing chain is on right. I dont know if that would cause such low compression though? Guy Quote Link to comment Share on other sites More sharing options...
Guest Magnum Rockwilder Posted November 6, 2004 Share Posted November 6, 2004 Are you at WOT when you do the compression test? It sounds like the distributor is 180 out, but that doesn't affect compression. All I can say is troubleshoot it. What in the hell made you go with a 4.3 instead of a SBC, anyways? Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted November 6, 2004 Share Posted November 6, 2004 Now its 90 at wot. I don't understand why its not firing good at all when it seems to be backfiring just fine. Even though its been sitting a long time and its cold is this so low of compression that it wouldn't fire at all? Would it even backfire? Quote Link to comment Share on other sites More sharing options...
72zcar Posted November 6, 2004 Share Posted November 6, 2004 . What in the hell made you go with a 4.3 instead of a SBC, anyways? leave the dude alone..he spent 4 yrs installing the 4.3... does sound like the timing in off...how did u check that you are on the compression stoke..finger over the spark plug hole trick? sometime this way is difficult to tell..best way is to pop the valve cover and watch the rockers on #1 cylinder. After the intake rocker opens and closes then continue turning until its on factory specs (might be 8 btdc not sure look it up) then point the rotor directly at #1..i mean right on it and it should fire. Compression does seem way low but it should start. Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted November 6, 2004 Share Posted November 6, 2004 I did the rocker arm trick to make sure it was on the right stroke. It still still backfires and bogs down a little. Thanks for the help so far, I'll keep tryin. I dont want to put a lot of money into this motor, I wanted to build up another one and just run this until did. Quote Link to comment Share on other sites More sharing options...
72zcar Posted November 6, 2004 Share Posted November 6, 2004 have you put a timing light on it when its running? Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted November 6, 2004 Share Posted November 6, 2004 It won't run at all. It doesn't even fire like its trying to start once. I mean it seems to bog down after it backfires or before like the timings off. Maybe the guy messed up when he put the timing chain on? Would the valve timing effect compression and backfiring? Quote Link to comment Share on other sites More sharing options...
wheelman Posted November 6, 2004 Share Posted November 6, 2004 Magnum, The 4.3L engine is capable of producing lots of power. I've got one in a Safari Mini-Van, it's rated at 200HP stock and with a few mods can make a lot more. It's also lighter than the stock Datsun motor so it's not such a bad install. It also uses the same motor mounts as the SBC so a JTR style setup can work. 4.3L 280z, Did you pull the cam or replace the timing gears and/or chain? If the cam is not timed correctly it could cause the low compression and backfiring through the intake. I would start there and once you've verified that then work on the distributor timing. If the timing is off you also run the risk of contact between the valves and pistons so don't try to run it to much before checking. If the timing is right then make sure the plug wires are on the correct plugs. Wrong plug wiring won't affect compresson but might cause the backfiring. Have the cap, rotor and plugs been replaced. These engines are sensitive to flakey ignition parts so make sure thet are in good shape. Keep us informed of what you find. Do you have any pictures of your install? I thought real hard about doing the same thing but went with an LT1 instead. Wheelman Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted November 7, 2004 Share Posted November 7, 2004 Well thanks for all the help but there wasn't any problem except for my stupidity. For some reason I was thinking backwards and installed the plug wires all backwards. It runs great . Now I just need to wait until Friday for test and tune at the drag strip 8) Quote Link to comment Share on other sites More sharing options...
CruxGNZ Posted November 7, 2004 Share Posted November 7, 2004 Sorry, I had a good laugh on that one. We ALL make mistakes though. !M! Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.