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VERY Long Cranking LT1 Swap

4269 Views 7 Replies 4 Participants Last post by  Desmo748
I have a LT1 swap here that is suddenly behaving very strangely. The engine is from a 1995 Camaro and has little done to it. No internal stuff, just Venom injectors(I know junk), Cold air intake, and true dual exhaust with h-pipe and cats. Has a brand new MSD Opti and MSD coil. Same old ignition module. It is in a 1983 Chevy Malibu and has a Street and Performance wiring harness that is brand new. It has started perfectly fine for quite some time now. Then a few days ago things suddenly changed.

While doing some tuning the other day and noting some fairly cold cylinders we decided to do a compression test. I pulled the fuel pump relay and all of the fuses in the engine harness(not marked which is the Fuel pump so just played it safe). Compression test was fine, so I put it back together and fired it up. The next morning first thing I came in and loaded a new file I had worked on the night prior(very minor timing and fuel changes). When I went to start it the car cranked and cranked. I was concerned my flash was corrupted so I tried to read it. Read fine. Reloaded the previous file to my changes. Still wouldn't fire up. Finally after cranking it for far longer than I like, playing with the throttle a bit, it fired up. When it is not wanting to start, as you roll off of the key you get a few diesely pops out of it and it pushes a tiny bit of smoke out of the intake. When it does finally fire up, it runs like a top. Perfectly fine. Took it out on the street and feels great.

If you let it sit for a few hours, or overnight, it becomes a hard starter again. Fuel pressure comes right up with one key cycle. It only comes up to 40psi KOEO. And about 35 psi idling. So I don't care for that a whole lot, though it is JUST below the spec.

I have spark and injector driver pulses a noid light when it is cranking and not seeming to fire. So honestly this make very little sense. VATS is deleted out of the tune and the Street and Performance harness has a VATS bypass module so even if it wasn't it would still run.

The only things I can think right now is I am getting a bad signal from the Opti for some very strange reason making timing of all events off. Or I am not getting nearly enough fuel volume. However why would it run well once it gets going if either of those was the case? The fuel pump is a brand new in tank unit, I am unaware of what pump it is.

Does anyone have any idea? The only way I can get it to go initially is to just crank and crank and crank on it. Datamaster is showing RPM during cranking as well.
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Does anyone have any idea? The only way I can get it to go initially is to just crank and crank and crank on it. Datamaster is showing RPM during cranking as well.
I'd Check those Venom injectors arn't leaking. I had 2 that weeped when I pulled them. I Didn't Trust them after that.
I Had 30# Venoms then went with 30lb Modified Bosch 3 Injectors ( Stainless later core ) from Welcome to for 189.95 USD

Yea a lot of folks have told me to watch out for those Venom injectors. So far I don't really see any issue. Of course I haven't had them flow tested.

Once it gets going, even before it warms up, it runs alright and starts alright. Once it is warmed up it runs and starts great.

Pulling the injectors up now to check for leakage anyway.

EDIT: Doesn't look like any injector weeping. Key cycled a handful of times with the injectors popped up. Maybe a very very tiny amount from one of them on ONE of the key cycles, but that was all.

I am almost wondering if I shouldn't take injector pulse width out of it at colder temperatures. But it was starting fine on those settings last week.
Did you happen to put the dlc in when you did your swap? If yes, I suggest hooking up to an obd1 scanner, preferably one that not only reads codes, but also does running sensor data scans.

First read your codes. If you have a check engine light hooked up, know that there are silent codes that don't light it up. Dtc 16- opti low resolution pulse missing, dtc 41 & 42 both icm related codes don't light the check engine light. If these codes are intermittent, it will cause starting problems, so also check the opti wire harness.

If you don't have a check engine light installed, codes like dtc 36- opti high resolution pulse missing, can make for hard starting as other codes can.

Check those injectors. Unbolt the fuel rail, lift them out of their holes. Then do key on prime and watch for leakage. Hopefully I don't need to mention safety precautions when working with gas.

I would download the 94 factory service manual available in 4th gen section. Volume 2 has a pcm wire symptom chart, that might come in handy for checking out your hard to start problem if no codes found.

Good thing to check is also pcm power leads, pcm grounds, as well as , engine compartment grounds.

That leads to the sensor data scan part of the obd1 scanner. You might get a clue to your hard start looking at your sensor readings. If sensor readings baffle you, would be glad to send you the pdf of sensor readings and what they mean. Just pm me with your e-mail address and I'll send it to you.

Whole volume 2 of 94 service manual would come in handy. Your 95 shares almost all the info with the 94. will have what is different on his site. Manual has wiring diagrams, component location diagrams, driveabilty testing and emissions.
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Thanks for the input. Oddly enough I haven't checked Codes, silly of me. I am running Datamaster on my laptop and yes the harness has a DLC.

I have been watching PIDS during cranking(when it doesn't want to start) and they seem fine overall. I have cranking RPM, pulse width seems maybe a tiny bit low at idle but I have made no changes to the startup fueling/spark. Coolant temp, intake air temp, spark advance, they all seem fine and not out of the ordinary.

I have full AllData access, thanks for the info on finding diagrams and all though.

I popped the injectors up this afternoon, no leakage I could see.

My next steps are to check out if any codes are tripping, check fuel volume, maybe throw my oscilloscope on the Opti, and maybe follow diagnostic procedure on the ICM. I've got spark and plenty of it thougha.

I know my way around diagnostics pretty well, this is simply being baffling. Especially since at the heart of it, nothing changed from one day to the next but the car suddenly acts totally different. One day it starts fine every time, suddenly it has this silly long fight to start up.
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Played with it a bit again. When it is stone cold it just cranks and cranks. Has spark but the spark looks a little weak(bulb style tester, misplaced my kv/gap style tester). Installed a new adjustable regulator, now KOEO I have 45psi, cranking/running 40psi. Introducing external fuel(carb cleaner) didn't make a difference. IAT and ECT are reading right on as far as an infared thermometer says. No DTCs tripping. I am really perplexed.

Next step is checking out the ICM and power to the Opti. Seems like maybe during cranking I am getting weak power to them? Doesn't really make sense as to why after the initial hard start it starts up easily.
Figured it out. Just posting so someone may have a thought if they ever have the same issue.

Had weak spark at the plug wires when it was acting up, but alright spark right out of the coil. Called MSD(new MSD coil afterall). They told me to swap it for a factory coil and retest. Very scientific testing method... I did, and sure enough that solved it. So the new Coil is bad and has to be sent off for replacement. Strange but that was it.
LT1 long crank

My 95 Trans Am, (190k/auto, owned since new, stock, minus cat, suspension mods) has had a similar problem for a long time. Over time I've replaced just about everything... Accept for the the pump and for some reason the coil.. I've learned to live with it figuring it was the pump bleeding off and pressure checks good.
Rarely starts first attempt without excessive crank, always fires and runs mint 2cd or 3rd attempt.. No other issues outside of a random low rpm miss that happens very intermittently.. Cant believe I never did a coil. Today's the day. Will post results.
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