Purchased 94LT1 w/160k. Had ripped elbow, ex. mani. leak, and opti miss. Used good elbow from my 93 for ride home(3+hrs). Started fine every time, even after sitting an hour or two once at home to change parking spaces. Fixed man. gasket and replaced opti cap and rotor. Now won't start. Swapped opti from the 93. No help. Used opti I rebuilt to put back on 93 and it runs great. Swapped ICM/coil, coil wire, and opti pigtail from 93. No help. All fuses at dash/underhood are ok. Got good spark everywhere. Have injector pulse. Fuel pressure 43psi at key on. Plugs/wires changed by previous owner. Pulled 2 or 3 and they still look ok. Upon close inspection wiring looks good. It turns over ok but sounds as if it's backfiring lightly, mostly through the intake, but once loudly through the exaust. I'm leaning towards a PCM/timing issue. Could one of the sensors be sending a bad input to the PCM causing it to do something funky to the timing? I also need to know what scanner I can use to check for codes. This 94 is OBD1 "hybrid". Guess using a nice free paper clip like on my 93 was just too easy. Please help end my frustrations, this thing is driving me NUTS!

 

Sounds like your Opti is on the fritz, there are tons of threads on here about diagnosing a bad Opti, not to mention the one stickied at the top of this forum, you might try that.

I had my Opti go out when one of my small coolant lines got a pinhole sized leak in it and was spraying a fine mist over my engine, somehow the coolant got into my Opti in the 5 minutes I drove it trying to find a good place to park. =(

 

I actually swapped a working opti from my 93 into the 94 and it still didn't help. Then just to double check things, I put the opti that was originally on the 94, with the new cap and rotor I had replaced, back on the 93. It starts and runs fine so I don't think it's the opti itself.

 

make sure you put the splined shaft on right. i had a friend that put one in backward and the car did not start. after a week he took it apart and turned it around and it started right up.

also once i thought i had an opti problem and replaced the opti, coil, wires, icm... it turned out to be a o2 sensor. with that exahaust leak it could be just that.

 

I think, from what I can see, the splined opti driveshaft is keyed in the same place on both sides. I didn't think it could be installed backwards although I did see a post that said turning it around might cause some oil leakage. Guess the seal in the timing cover would rub on a slightly different part of the shaft if it was installed opposite of original. Never really thought o2's would cause a no start unless maybe the wires were totally shorted or something which they're not. Thanks for the ideas.

 

Somethings not right! You claim to have fuel and fire, all that is needed now is compression. Double check your grounds.

 

You can use a generic OBD-I scanner. You can find an Auto-Xray for under $100 used on eBay. Or you can use software with a laptop and a cable.

FreeScan (= "free" download)
http://www.andywhittaker.com/

TTS DataMater ( = "free" download, 20 free uses)
http://www.ttspowersystems.com/

Cable:
http://www.akmcables.com/

Guideline on interpreting the scan data:
http://www.injuneer.com/Scanner.html

How did you verify the injectors are pulsing? 'noid light? Did you verify the pulsing continues for more than 2 seconds when you are cranking it to start it?

You appear to have done a number of Opti installs, but is there any chance you didn't get the notch in the splined shaft aligned correctly? It can and has been done (frequently, based on posts on this forum).

 

i didnt think so either but a friend of mine that works on alot of LT's told me it happened to him once and when he turned it around it started. as for the O2's that happened to me, they where going bad for awhile but one day the car just wouldnt start. after checking everything and replacing alot of thing still nothing. changed the O2 and it started right up.

 

I used a multi-meter set on the 10-50v DC scale hooked between the two wires on a few injector connectors to check for pulse. As I cranked I could see the needle move up in a pulse-like pattern. I figured this was an indication of good injector pulse. I checked my grounds, including the one on the side of the motor for the PCM and the cluster on the ICM. The more I think about this thing the more I suspect timing issues. I tried to start it today and again all I got was that soft, gentle backfiring sound thay seems to be coming from the intake. I sprayed start fluid through the throttle body and all that did was make the pop a little more pronounced. Seems like it backfires primarily through the intake. In all the times I've attempted to start it it only backfired through the exaust once. I believe the opti is on correctly. It's flush w/the block and I didn't have to force it on at all. At one point I also took the valve cover off and with cyl. 1 at TDC the rotor pointed at the cap terminal for cyl.1. I didn't really check to see if they were perfectly aligned though. Which leads me to my next thought. This engine does have 162k on it. It looks like it wasn't taken care of all that well. The intake is awfully carboned up(I guess from the previuos owner running it with the ripped intake elbow). I changed the oil and as the last little bit drained I noticed it looked real thick and sludgey. Could excess friction have caused a premature timing chain issue? Haven't seen many posts about problems with them but now I'm beginning to wonder if that could be the culprit. Again thanks for the input. I've been a fan of this awesome website for a long time

 

You will get an injector pulse for the first couple of engine rotations when you try to start the car. But if the PCM doesn't find the low resolution pulse in two revs, it shuts down the fuel system, including the pump and the injectors. That would indicate a problem with the optical sensor in the Opti, or a problem with the harness. A scan would show if this is a problem, because you will get DTC 16 if the PCM can't find the low res pulse.

 

I have a good one for ya. I have gotten a DTC 16 and the car runs with it lol. It was an opti problem but I always thought with that code you would have a no start no run condition.......first time for me on that one. I completely agree with what he tells you on the 2 second pulse verification.

If that turns out not to be the problem then you should check for compression. As I stated earlier you have two of three (Fuel and fire) by your posts so check the third.

 

Found it! The small splined shaft between the opti and the cam had worn to the point that it would fit into the opti easily in any position. And I mean EASILY. That's what was causing the timing issue. Thanks all for the ideas.

 

are you gonna use another one from another opti or get a new shaf? if you find a place to buy the shaft please post where you found it.

 

The shaft works fine I just have to make sure it's installed properly by visual inspection since I can't trust the little weld to key it into the opti anymore.

 

i had my 94 z28 act the same way and it was the airbox intake connection to the throttle body