LT1 in CJ: Help w/Diagnosing No Start

[Mikiewpb]

Hey Guys - New to posting here but an avid reader. I'm in the last stages of an LT1 swap into a '78 CJ but she doesnt want to start. I've listed below a summary of tests performed, components replaced, etc. to see if anyone has any thoughts on what my problem could be. This motor is from a junkyard and we’ve never seen it run.

v Biggest problem that we see is that we’re not getting any vacuum at the intake?? The MAP sensor reading on the scanner with the key off is absolute pressure (30). Only goes down to 28.3 when cranking.
v Tested MAP sensor as per ShopKey instructions and all tests came back good. However, when we first hooked up the scanner that day before performing the tests, we showed Trouble Code 34 which is the MAP sensor.
v Pulled MAP sensor and put a mechanical vacuum gauge in the hole and got very little to no vacuum.
v Only got up to 175 RPM when cranking.
v TP started at .96 (didn’t write down the reading at WOT)
v Coolant Temp at -40 spikes to 46 when cranking
v MAT: 25
v Checked OHMs on ETC on water pump and ITS as per ShopKey and all ok.
v Opti that came with the motor was bad (tested using scanner) and replaced.
v IAC new
v New spark plugs
v Pulled valve cover and confirmed timing was ok by viewing the piston location and valve operation at TDC#1 (compression)
v There seems to be a ton of carbon in the intake?? Even after just cranking with the new spark plugs, they already have some carbon/junk on them?
v Getting spark at all spark plugs.
v Fuel pressure is 43 with vacuum off and stays there when cranking.
v Injectors cleaned and got them all to fire and flow carb cleaner while out of the vehicle
- Compression: All cylinders between 140-155 except for #2 at 125
- EGR removed and blocked off

Any help would be much appreciated!

Thanks
Mike

[terminal_crazy]

You've got fuel spark & Compression.
I'd check timing.

Is OPTI set correctly?

[Workman]

It Does sound like the Timing is off, I had the same exact problem with my old 350 rebuild, We tried everything in the book, but finally realized the timing may need to be adjusted/was possibly off, So we re adjusted the timing and Boom, Turned the key one time and she fired right up! driving her a few hours later no probs [= Let us know what happens when you check the timing.

[steveo]

getting no vacuum while cranking is a huge concern. vacuum in that map sensor hole should be readable while cranking. reason could be a giant vac leak (the intake is loose or something)..

it should start regardless of a failed map sensor. all the same, you should actually just plug the map sensor in, apply vaccum to it with a vac pump, and check the value with a scanner. that rules out wiring

coolant temp at -40? you have to fix that too, its important.. the ecm will think it needs a gallon of fuel to start because its so cold. no wonder its full of carbon, huh

-40 is max resistance; you have a broken wire, the sensor is unplugged, or the sensor itself is screwed. test the sensor, if its good, fix the wiring. 4th Gen LT1 F-body Tech Articles

maybe you can tell us a bit about what you did with the wiring during the swap, if you changed anything, etc..

real bitch about these engines is their wiring is very small and fragile (gm made 'em that way to save weight/money) so it's really common to swap an engine wiring harness into a different car and break a wire or two, just from bending/moving it around

luckily testing the entire harness doesnt even take that long (i just did one..)

also you didnt mention what year car this engine is from, would be nice to know..

[steveo]

Originally Posted by Workman

It Does sound like the Timing is off, I had the same exact problem with my old 350 rebuild

these are an electronic cam trigger ignition system...

you cant mis-time an opti unless you cram the dowel in the wrong hole.

[sweetbmxrider]

Aside from what steveo said, have you verified the injectors are opening while cranking? You can just pull the fuel rail a couple inches off of the intake and watch. These cars use a pretty simple antitheft referred to as VATS. If you google a bit, you will find plenty of bypass step by steps.