Engine removal/crank but no start

[Mikey1528]

Hello r3v, first time poster, longtime lurker.

I know this has been covered before but i need to get the car running asap and have been following the no start check list. I just finished my m20 rebuild 3 weeks ago, reinstalled everything, fired up within seconds and seemed to run fine. still haven't run it for more than 30 seconds. a few days ago i removed the engine and trans with wiring intact as a whole to do the clutch, reinstalled everything and am now having a crank no start issue. if i let it sit for at least a couple hours, it fires once almost immediately but then continues cranking. im running motronic 1.1 so cant really pull any codes. ill be trying out a 1.3 on Wednesday to trouble shoot though. im not sure what could've have gone wrong from the time i pulled it to the time it went back just a few days later. it seems like a wiring issue but ive double checked all connections unless there is a short somewhere.

So far it it has...
-spark when cranking. verified timing belt timing again to make sure it didn't jump timing.
-fuel at the rail (injectors are rebuilt), tried bypassing the fuel pump relay when starting, same result. I replaced the fpr for good measure, same result. haven't test fuel pressure but seems solid, and was fine a few days before.
-checked the cps resistance, read ~550 ohms at dme and sensor.

Thanks and sorry if this has been covered.

[Ceeker]

starts and runs then cuts out? what about the main relay? Also make sure your CPS has continuity. If it is shorting it will stop sending the signal to the DME and cut the fuel supply off.

[Mikey1528]

Thanks Ceeker. well, i wouldnt say runs and then cuts out, but i can here it fire for a split second almost as soon as it turns over but then it goes back to cranking. i do need to check the main relay though. if im getting 550 ohms at the harness connector for the cps that would mean i have continuity correct? and if it is shorting, would i still get fuel when i bypass the fuel pump relay while starting? also my check engine light (not the check light) is on even after unplugging the battery,letting sit, and reconnecting, ive read this may indicate a faulty dme?

[jlevie]

That can also mean that the DME isn't getting good power or a good ground.

[YosemiteSam]

if im getting 550 ohms at the harness connector for the cps that would mean i have continuity correct?

Yes, getting 550 ohms on the CKP is continuity, and IIRC that is within spec. (I'll try and double check spec in my Bently manual after work tonight)

if it is shorting, would i still get fuel when i bypass the fuel pump relay while starting?

If you are asking if you would still get fuel out of the fuel pump and have fuel pressure at the rail, then yes, you would still get fuel to the rail.
If you are asking if jumping the fuel pump relay would make the PCM pulse the injectors and deliver fuel to the cylinders, then no. The fuel pump relay has no control over injector drive. If the PCM is not seeing a CKP signal it will not deliver fuel to the cylinders. This being said, the PCM also controls spark, so if the CKP signal were cutting out you should also be losing spark.

Based on your problem I would try one of two things, I would check for injector drive if you have the tools/know how, or I would have a friend crank the engine while you spray some carb cleaner or starting fluid in the intake.

[cscracker]

Make sure your crank position sensor and top dead center sensor plugs aren't switched. They're right next to each other and have the same plug. I had mine backwards when I replaced my head, and had this problem.

[Mikey1528]

Thanks guys,

I ended up trying a different dme today and it fired right up and seemed to be running fine during cam break in, may have a slight occasional miss though, its hard to tell. im not sure what would cause the other dme to fail at the same time i pulled the engine unless it was already on its way out (received the car in an almost non running condition), but i will continue checking the wiring for any potential intermittent shorts or bad grounds and am replacing critical relays for good measure.