russ in va Posted August 13, 2007 Share Posted August 13, 2007 I bought my 280zxt powered 1970 240 a couple of weeks ago. At first, it ran strong like a 150-160 rwhp 240 should. Then, all at once it was WAY down on power even though it still starts and runs perfectly. I've since had it on a dynojet and sure enough, I'm only putting 85 hp to the ground. Air fuel is about right. The plugs all look good. I'm making 7-8 lbs of boost. I am getting full throttle. I'm left scratching my head??? My current next step is to check the compression, but since it went from right, to off like a light switch was flipped I doubt that's going to find any problems. Any suggestions are appreciated! Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 13, 2007 Share Posted August 13, 2007 Ignition timing might be off? Check the advance of the timing as the revs increase. Also check your cam timing. DOnt forget to check the air filter and any air flow blockages anywhere. Quote Link to comment Share on other sites More sharing options...
russ in va Posted August 13, 2007 Author Share Posted August 13, 2007 I want to check the timing, but I don't have a service manual for the donor car. As I understand it, the ECU does control timing on the ZXT, yes? Yet, the distributor is clearly adjustable and there is a timing scale down by the crank pully ... so what are the timing specs? Is there anything to unplug in order to properly set the base timing?? Thanks! Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 13, 2007 Share Posted August 13, 2007 check the downloads section here. There is a link to downloadable service manuals. The ECU controls timing in a linear fashion with RPM. You can set the base timing by turning the dist. There is a dial indicator on the pass. side of the timing pulley. Quote Link to comment Share on other sites More sharing options...
wigenOut-S30 Posted August 13, 2007 Share Posted August 13, 2007 If you have the stock ZXT knock sensor plugged in. It could be hearing head noise, see it as "knock" and pull all of your timing out. Do you have a wideband? I am guessing this is a stock ZXT motor with stock T3 turbo and running off the wastegate. make sure you use a wideband.. and if you can get back to the dyno.. do a pull with the knock sensor installed and then try it again with it unplugged. just make sure you pay close attention to the wideband.. Good luck man.. Quote Link to comment Share on other sites More sharing options...
russ in va Posted August 15, 2007 Author Share Posted August 15, 2007 I thought about the knock sensor, but not until after I left the dyno. I unplugged it on the street and could not tell any differnce, still dog slow. I did a compression check a few minutes ago, and thankfully did not find anything wrong... 142-150 psi across the board (I don't know what "normal" is, but the numbers were all close enough so that made me happy). Hopefully I'll have time to check the timing in the next couple of days, I'm dying to start driving this thing! That FSM download site rocks! Waiting for the 82 ZX to come available for download so I can get it. Quote Link to comment Share on other sites More sharing options...
russ in va Posted August 26, 2007 Author Share Posted August 26, 2007 OK, timing was the problem!! I had 0 base timing (I think it must have moved somehow between when I first bought it and it drove fine, and now when it doesn't ... but how ??? The distributor was not loose and I had not touched it before??). Anyhow, I upped it to 20 degress (that's as far as the dist would turn!). But, it did not change as I revved it up!? I drove it and it was much better but still seemed a bit flat. After my buddy went home and took his timing light with him, I discovered that the round CAS plug that leads to the bottom of the dizzy was loose. Now I need to recheck timing. What would unplugging it do? Quote Link to comment Share on other sites More sharing options...
russ in va Posted August 27, 2007 Author Share Posted August 27, 2007 OK, so I just tried unplugging the CAS plug to the distributor and with it unplugged it won't run at all so that's not it. I know this distributor does not have mechanical (or vacuum) advance, but shouldn't you be able to watch the timing change from the base setting as you rev the engine? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 27, 2007 Share Posted August 27, 2007 Yes the riming should advance as you rev it. You might have a bad distributor or bad CAS inside the dist. Before you incriminate them, check the wires from the dist to the ECU with an OHM meter. Try another distributor if you have access to one. Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 31, 2007 Share Posted August 31, 2007 If the CAS was bad, the timing wouldn't work at all IMO. The Computer changes timing based on inputs like RPM and AFM resistance. The ECU may be funky, I don't see how a CAS failing (failure mode would be to drop out signals and not get a spark) would cause timing not to move. Misfiring, yes, timing change is totally inside the ECU. Quote Link to comment Share on other sites More sharing options...
savageskaterkid Posted August 31, 2007 Share Posted August 31, 2007 bring it by my place this weekend, and we can figure it out. Maybe even have 2 Z's running, in the same place, wouldn't that be nice. Quote Link to comment Share on other sites More sharing options...
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