420a wont fire

[shaunm]

I've gone over this forum a few times and have not found a thread solved with the problem Im having. This might be a bit long of a post and probably wordy.. But I've got a 98 n/t that spun a bearing.. Pulled the entire engine and swapped with a junk yard 420a. The 420a I swapped with had a different plug for the CPS. (assuming 95-96 2ga) I took my 98 sensor that fit the plug and replaced it. CAS I believe was the same but could be wrong, I just replaced both sensors w/my old. Engine was fine until the bearing, so sensors should be good.

Car wouldnt fire. Turns over all day long. No fire. Assumed timing- rechecked- timing was a tooth and a half off, fixed that. Still no fire. Found compression was weak in cyl 1, figured head gasket or bad valve. Replaced the head with the old head (2gb) from the original 420a. Same problem.

Figured at this point I would just do a full lower rebuild on the new engine since I dont know the entire history behind the engine. After a month, on and off the lower end was rebuilt. No crank scoring and the cylinder walls looked great. Rebuild went fine. Still using the old head (again no upper issues with the engine)

Put the engine back in, no fire. Still. Fuel pump kicks on, pressure (unknown how much) in the rail, Auto shutdown relay clicks, no problems what so ever.

Engine back out- took the 2ga head lapped the valves, and replaced the lifters. Put the 2ga cranks back in it, and ported it since it was out of the car anyway..

Same problem - turns over all day long, no fire.

Checked continuity from ecu harness to every pin on every plug in the engine bay- no prob. Continuity to the relays- no prob. Got a hold of some starter fluid - engine fires. runs on starter fluid - BADLY but at least I know now Im getting spark and fire.

Replaced CPS, CAS, and Coil pack, plugs, and wires. - nothing same problem.

I feel like I threw the kitchen sink at this thing.. So aside from the obvious question - why doesnt the thing start up on its own - I do have an unanswered question.

Would a 2ga sensor send different signals to the 98's ecu - and just be misreading the 2ga's crank because its a 98 sensor? And if it IS that simple - would picking up a 95 Crank sensor fix this whole problem all together?!

Or am I looking at swapping the 98 ecu for a 95 - and/or tearing the 2gb crank out (hoping its not seriously chewed up from the bearing) and putting it in the 2ga block...

Please any advice will certainly keep my sanity at this point.

 

[94stealth]

im not 100% these could be your problems but it wouldnt hurt to check if compression was low on one cylinder its possible the rings are bad. not enough compression it wouldnt fire. forgive me for not reading all of your post but did you check plugs? plug gap? after you replaced all that stuff it has got to be something little. hope this helps good luck!

 

[shaunm]

Yeah, checked all that. The block was rebuilt. Same pistons, new rings and honed the cylinders out.. Plugs are new, gap no prob.

 

[94stealth]

and if its not any of those or a fuel problem, im at a loss for words. ive never heard of replacing ALL that and it not firing. if its getting air, fuel, and spark then it has got to be an electrical problem but im not sure what it could be. is the air/fuel possibly way off? or maybe you have a serious air leak somewhere? sorry i cant be of more help man. but good luck!

 

[coryd21]

First off if the car will start on starting fluid then you are not getting the fuel supply you need. I would check for a clogged fuel filter and find out exactly how much fuel pressure you do have or the FPR could have went bad and not holding fuel pressure.

Secondly just b/c you have continuity doesn't mean the wires are exactly good. It would only take one wire out of the whole strand to have continuity. Do VOLTAGE DROP tests on the proper wiring and you will know for 100% the condition of the wiring.

Also see if the vacuum line to the fpr is good or not b/c if you don't have a vacuum to it, it won't work properly.

 

[idomin8-420a]

having the same problem but make sure the transistors in the ecu are good or that the ecu you are switching matches your oem ecu this makes a bit of a difference but ill be posted and keep u updated on what i find thats new good luck

 

[shaunm]

Ok, good news, Wasnt a vacuum line problem, nor the FPR thankfully. I gave it the hail mary pass this weekend and pulled the engine back out.

I verified head bolt torque, they're currently tight at 80ft/lb. I retimed the engine, probably the rookie way this time but its timed. I had the cams unbolted, I got the t-belt on, plunger was pinned shut, stuck a screw driver on the bottom of the tensioner to prop it up, bolted it in, bolted the cams down (while the hashes being dead set even) and released the pin.

Replaced the temp sensor AND got a 95 crank sensor. (again assuming the original problem was the gen2 98 sensor was reading the 95 gen1 crank).

Dropped the engine back in the car- primed the fuel rail, turned the key over- after about 6 turn overs it fired up and idled.

I do have a header on it, w/o an O2 sensor on it or the down pipe, the CEL light is on naturally- but after reading it, its for the cam sensor. (1st gen cams, 2nd gen sensor) ?? maybe. However- its running, and running better than I thought. So.. thats all I got, hope that helps.

PS some technicals Ive missed in the last few posts.
I did check fuel pressure, was at 50psi at its highest. It does drop, though only a little. (maybe the o-ring)
Same stock 98 ECU, it works CEL would light prior to cranking.
Timing on #1 if I read the obd correctly was at 6 deg while idling.
Idle is pretty smooth @ around 875rpm
Head is exhaust ported and polished, and valves lapped.
I did not get final compression reads on the cylinders


I suspect, and I am probably incorrect- but the 98 crank sensor was completing the Auto shutdown circuit providing spark and fuel pump- however misreading the crank therefore no injector pulse.
-or-
the temp sensor was so jacked it was compensating for some unrealistic temp and leaned the fuel out to virtually nothing.