93 Z34 engine dies and wouldn't start - crank but not turn over

[Laveen Z34]

Fellas,

 

It appears that my Z34 will be seeing the graveyard pretty soon if it does not come out of this rut. Cruising @ 50 mph and all of a sudden engine died and wont start. Cranking the engine but won't turn over. Fuel pressure was good and I actually took it to the shop. It ran for two days but it decided to start this time from my work parking lot - crank but not turnover. Back to the shop. Still there and mechanic said it was doing the same thing. He said there was spark and fuel pressure was good. He's thinking of replacing the ICM module as he is running out of answers. This Z34 has a new fuel pump, fuel regulator, fuel rails checked and cleared, new plugs and wires, all wiring checked, even replaced oil pressure sensor as it was too corroded. I also saw fluctuations on the voltmeter below 12V and not quite sure if thathas something to do with. Starter is good. So pretty much, has anyone had this problem before? Needs advise if it does not run, i guess it's time to part ways with my Z34.

 

Please help!!!!!

[GTP091]

What do you mean by 'crank but not turnover'? crank and turnover mean the same thing to most people.

 

Engines need fuel, spark and correct timing to run if they have all 3 in reasonable condition they should at least run rough. There must be something off on one of these 3. You say there's fuel pressure and spark so maybe the ECM is screwed up it runs the show on all 3.

 

First thing I would check is the crank position sensor. It gives spark timing to the ICM. If it's damaged or malfunctioning the engine will not have correct ignition timing. I had thought if it goes there will be no spark at all but maybe a faulty sensor causes misfire? worth a check before replacing the ICM

 

Did you check the timing belt condition. Unlikely it broke but maybe one of the pulley is messed? Doubtful it's the issue as it should cause rough running if out of time by jumping a cog and not do this while @ cruise. easy to check pull the covers and have someone crank the engine over to see if the belt moves.

 

How about the fuse for the fuel injectors? check all fuses in the electrical centre under the hood.

 

Did they test the ECM?? do you have a good spare to swap?

 

Your mechanic should have checked all this stuff, I would ask for another mechanic if he's out of ideas. it's a car not a woman, if a part or system is messed up it can be figured out by troubleshooting and can then be fixed; unlike a woman.

[AL]

I would replace the icm

[z34Phoenix]

my 96 dohc died a similar way... i did a compression check and discovered a high of 35psi!!!! timing belt was tight and looked good. i ended up doing a 3800 swap because of it. the shop that helped with the swap decided to tear down the dohc to see what really killed it. turned out the chain that drives the timing belt has a tensioner... it broke and a piece of it got stuck in the chain. every time it would turn it would jump timing on the engine.

 

bottom line is if you have fuel and spark, do a compression check.

[Laveen Z34]

I would replace the icm

 

AL,

I replaced the ICM and still did the same thing (ran, died, and wouldn't start). Do you think it could be the ECM now?

[Laveen Z34]

What do you mean by 'crank but not turnover'? crank and turnover mean the same thing to most people.

 

Engines need fuel, spark and correct timing to run if they have all 3 in reasonable condition they should at least run rough. There must be something off on one of these 3. You say there's fuel pressure and spark so maybe the ECM is screwed up it runs the show on all 3.

 

First thing I would check is the crank position sensor. It gives spark timing to the ICM. If it's damaged or malfunctioning the engine will not have correct ignition timing. I had thought if it goes there will be no spark at all but maybe a faulty sensor causes misfire? worth a check before replacing the ICM

 

Did you check the timing belt condition. Unlikely it broke but maybe one of the pulley is messed? Doubtful it's the issue as it should cause rough running if out of time by jumping a cog and not do this while @ cruise. easy to check pull the covers and have someone crank the engine over to see if the belt moves.

 

How about the fuse for the fuel injectors? check all fuses in the electrical centre under the hood.

 

Did they test the ECM?? do you have a good spare to swap?

 

Your mechanic should have checked all this stuff, I would ask for another mechanic if he's out of ideas. it's a car not a woman, if a part or system is messed up it can be figured out by troubleshooting and can then be fixed; unlike a woman.

 

GTP091,

I appreciate all the help. Fuel pressure - good, spark - present, CPS - good and replaced about a year ago, timing belt replaced a year ago and everything checked and mo messed up pulleys, all fuses checked, ICM replaced last week and still did the same thing. ECM is the only one left - where can I find and buy a decent one?

Again, thank you Sir!

[AL]

Try a compression check

[Gunboat]

I had the same thing happen to me,found out it was the crankshft position sensor,change that and it should work,if not,then go for the ICM..

[GTP091]

GTP091,

I appreciate all the help. Fuel pressure - good, spark - present, CPS - good and replaced about a year ago, timing belt replaced a year ago and everything checked and mo messed up pulleys, all fuses checked, ICM replaced last week and still did the same thing. ECM is the only one left - where can I find and buy a decent one?

Again, thank you Sir!

 

You've changed all the main stuff. I would rule out ignition based on that. Fuel pressure is good so unless it's the injectors; fuel is fine. If fuel and spark is there than the only thing left is timing. If the valve timing is out it will usually fire or backfire if off a little bit in the case of a jumped cog or to. Is the belt actually turning when you try and start it?

 

The ECM controls the fuel/spark timing based on CPS and other engine sensors. If it's buggered the injectors and spark could be out of sequence. Not sure if NAPA or autozone assuming your in the US can test the ECM? maybe give them a call and see. I;ve never asked.

 

You can get an ECM from the JY just make sure to match 91-93 LQ1 and same ID #. Robert Sarr will know the #'s I'm sure 177 something? If you get the spare put your EEPROM in the JY ECM and try it. if it's same year, car model, tranny etc. you can probably get away with just replacing it without touching the EEPROM if that works make sure you take the old EEPROM out before you throw the ECM away. again Robert will have better advice on this.

 

not sure what else you can do - don't give up though. hate to say it but double check with a bright light all harnesses are plugged in. might find you fixed the problem but forgot to plug in a critical harness.

[Galaxie500XL]

There's a pretty easy check for valve timing on the LQ1...

 

Turn the motor by hand, and get the harmonic balancer to TDC. Remove the front timing belt inspection cover, and the front valve cover.

 

If the engine is in time, the flats on the cams ( seen in the "hole" in the cam carrier, right behind the cam gears) will be parallel to the deck surface of the cam carrier. Keep in mind, the cams rotate at half the speed as the rest of the engine, so don't panic if you don't see the flats on the first attempt...if they're not showing, turn the engine one full revolution further, then check the flats again. BOTH front cams should show the flats in EXACTLY the same orientation, regardless. If one is turned farther than the other, and the flats can't be lined up in a straight line, the cams ARE out of time...or, at least one of them is.

 

You can check the rear cams the same way, but since that involves removing the plenum, and you're looking for a quick check, I didn't suggest doing that just yet.

 

If the flats are NEVER lined up when performing this check, the cams ARE out of time.

 

You've changed all the main stuff. I would rule out ignition based on that. Fuel pressure is good so unless it's the injectors; fuel is fine. If fuel and spark is there than the only thing left is timing. If the valve timing is out it will usually fire or backfire if off a little bit in the case of a jumped cog or to. Is the belt actually turning when you try and start it?

 

The ECM controls the fuel/spark timing based on CPS and other engine sensors. If it's buggered the injectors and spark could be out of sequence. Not sure if NAPA or autozone assuming your in the US can test the ECM? maybe give them a call and see. I;ve never asked.

 

You can get an ECM from the JY just make sure to match 91-93 LQ1 and same ID #. Robert Sarr will know the #'s I'm sure 177 something? If you get the spare put your EEPROM in the JY ECM and try it. if it's same year, car model, tranny etc. you can probably get away with just replacing it without touching the EEPROM if that works make sure you take the old EEPROM out before you throw the ECM away. again Robert will have better advice on this.

 

not sure what else you can do - don't give up though. hate to say it but double check with a bright light all harnesses are plugged in. might find you fixed the problem but forgot to plug in a critical harness.

[Scott205]

If you are sure you are getting a spark, and the injectors get pulse, and there is pressure then you are looking at a mechanical issue. I am having lots of problems with my Crankshaft Position Sensor and the harness that goes from there to the ICM. Just cuts the ICM and the engine stops. Didn't start for 3 days.. replaced the CKP ran good for the mechanic until that afternoon, then he went to the store.. wouldnt start. He found a short at the top of the harness near the ICM, but guess what.. ran good for this week until friday.. now the engine stop every 5, or 1 or 3 minutes... usually restarts first try.. must be another short.