I've been working on a 85Z, 305 TPI (not mine, but a side job for a buddy). I just replaced the engine with a rebuilt 305, all stock, just added Hooker shorty headers. I took over for the guy who started doing this, so when I got to it the top end of the engine was all apart & the engine wasnt pulled, so I had fun getting all the vac hoses back right again I got it all but the EGR valve & solenoid. Can anyone tell me where the hoses should go from the solenoid?

Its got other problems though.It will idle good, but dies as soon as its put in gear. The cooling fan doesnt come on (motor is tested good). I also cannot pull any trouble codes out of it, I jump the ALDL & get nothing. I even replaced the check engine bulb to be sure that wasnt bad.

Any thoughts? Vacuum reads a rock steady 18" at idle, fuel pressure is 42psi, initial timing is at 8*. Right now its only got open headers till we get it to the muffler shop to make a Y-pipe, the O2 sensor hasnt been reinstalled yet. I dont know much of the history of the car. Its been sitting for 2+ years with a blown engine, which appeared to be from massive overheating (bearings were welded to the crank). I assumed this was caused by the fan not working.

 

EGR vacuum hose. If I recall it comes off the TB- one of the small vacuum ports that has vacuum ALL THE TIMES. From there over to the solenoid and from there to the EGR valve itself. There is a 3rd "port" on the solenoid itself that looks like it should have a hose but it does not. This is where the solenoid "bypasses" the vacuum when the ECM does not want the EGR valve to be open (i.e. 0% EGR solenoid duty cycle). The solenoid simply determines how much of the actual engine vacuum to send to the EGR valve based on what the ECM commands. It works on a "duty cycle" principle like a fuel injector- 0%, 25%, 50%, etc. on up to 100%. More duty cycle, more vacuum sent to the EGR valve.

No trouble codes, eh? Sounds like the ECM is shot. If you are jumpering the correct 2 pins it should start flashing the check engine light. Code 12 means all's cool.

Given that you don't have the O2 connected you should have AT LEAST an O2 code in there in addition to the code 12.

Can't remember how the fans work on an 85 but in all cases there should be a sensor screwed into the pass. side cylinder head between #6 and #8 cylinder exhaust ports. That's your "switch of last resort." It's job is to turn on the fan(s) if for some reason the other systems fail. Grounding the single wire that goes to that sensor should turn on the cooling fan(s) regardless of whether the ECM or other things are working correctly. If grounding that wire does not turn on the fan(s) then you need a new fan relay. I think the fan relay is located behind the pass. side headlight near the radiator, but don't quote me on that.

On cars where the ECM typically turns on the fans that "switch of last resort" will not kick them on until about 240* (way too hot). On cars that the ECm does NOT control the fans that switch should be set to turn on around 215-220. Lower temp switches are available from the aftermarket if you don't want to trace the problem completely but also don't want to hard-wire the fan to run all the time.

 

As far as the engine shutting off when you put it in gear, I had the same problem and after a lot of trouble shooting it ended up being a bad prom in the computer. It does not cost that much to replace it might be a good place to start.

 

Swap out the ECM and EPROM with a known good one. I assume you covered all the vacuum leaks, etc? 42 psi -45 is allright for fuel pressure but to diagnose somethign like this, you need to hookup a scanner. Also timing should be 6 deg. With a scanner, we can see the IAC counts and know why it is doing what it does. Are you sure the SES light works? IE, can the ECM actually activate it? Is the wiring ok?

 

Thanks all!
I got all the vac hoses sorted out, put the O2 sensor in the header & ended up tossing a new IAC in -cleaned the old one & noticed it was frozen. Car still runs the same. I'm leaning towards a bad computer or prom. I have checked the SES bulb (even replaced it to be sure that wasnt it). No go. The only time the SES light comes on is occasionally on engine start-up, even then its just a quick flash.

Would the car even run with a bad computer or EPROM?

 

Got scanner? That seems normal. Short out the ALDL and see if you get code 12