91 300zx 5-speed LS swap issues....

[cm1wrx]

Hello, I will do my best to keep this as simple as possible. I just finished LS swapping my 91 300zx 2+2 and I cannot get this thing to start. I have searched all over the forums, made two separate "start up maps" based on youtube tutorials (goat rope garage and Matt Sanford) in both traditional and speed density and am having no luck. It acts like it want's to fire but wont. Cranking is somewhat consistent if the battery is full. (its the battery specs for Nissan, not GM so it might be a little undersized but I have an old school, plug in jumper pack that puts out 75amps). Occasionally I get a stumble and then back to cranking but that's it. The setup I did based on Matt's information has been the most functional so far (speed density) and I was able to get a short log (while cranking), which I have attached. If someone could just look at it and give me an idea of what I might have missed, I would greatly appreciate it!

Car
1991 300zx N/A 2+2 5 speed

Engine
2002 Chevy Tahoe 5.3 that I freshened (new rods, cam and crank bearings, rings gaped for boost, which is my future plan, etc.) all good quality, stock replacements. The heads are stock but were freshened by a reputable head re manufacturer.

Modifications to the engine-
First, I went through the entire motor and replaced all bearings, gaskets, oil pump, etc. All fresh and new "ish". The heads were re-manufacture stock from a reputable company. Just stock truck heads.... nothing special.
Running a Sloppy Stage 2 cam, springs, retainers, etc. and new lifters
Intake manifold is a Speedmaster unit (old style for ls1's) needed it to fit under the hood and not be made of plastic (I plan to go boost)
102mm Throttle body (sorry, I did this on the cheap... its a budget build but I used an Amazon unit.... hate if you want)

Wiring and Sensors
PSI wiring harness purchased through LOJ (they have the best fitting parts and have been doing this swap for a while)
LS3 MAP
5-pin style MAF (has IAT in it also) (I bought the part number they recommended but I know I can just run speed density and delete it, which I plan to do)
Cam and Crank sensors are new stock replacements
I don't have any knock sensors installed currently. I'm still trying to determine what setup I should use but they don't matter for starting purposes (meaning the engine will start without them)
Coolant Sensor was moved to the passenger side rear of the head and replaced with a new unit
Injectors are stock truck injectors currently (with a ton of miles on them but I cleaned them internally with a kit I bought) I also have a brand new set of Holly 100lbs/hr that I was planning to install when I go turbo.
Fuel rails are JEGS for LS1 style manifold and I am running a dead head system with a corvette fuel filter (58psi setup).


Car has full exhaust right now with stock replacement O2 sensors.

That's all I can think of at the moment. When I look at the log, I can see a couple of numbers that seem "off" to me (example: one of the channels monitors computer voltage... I noticed it was over 12v at the beginning and just above 10 by the end, then recovers once I stop cranking (full battery charged with a tender, not running the jumper pack at all when I did this) but I don't understand it well enough yet to confirm. Any help would be greatly appreciated!start up first log file still no start.hpl

[cm1wrx]

Hello, I will do my best to keep this as simple as possible. I just finished LS swapping my 91 300zx 2+2 and I cannot get this thing to start. I have searched all over the forums, made two separate "start up maps" based on youtube tutorials (goat rope garage and Matt Sanford) in both traditional and speed density and am having no luck. It acts like it want's to fire but wont. Cranking is somewhat consistent if the battery is full. (its the battery specs for Nissan, not GM so it might be a little undersized but I have an old school, plug in jumper pack that puts out 75amps). Occasionally I get a stumble and then back to cranking but that's it. The setup I did based on Matt's information has been the most functional so far (speed density) and I was able to get a short log (while cranking), which I have attached. If someone could just look at it and give me an idea of what I might have missed, I would greatly appreciate it!

Car
1991 300zx N/A 2+2 5 speed

Engine
2002 Chevy Tahoe 5.3 that I freshened (new rods, cam and crank bearings, rings gaped for boost, which is my future plan, etc.) all good quality, stock replacements. The heads are stock but were freshened by a reputable head re manufacturer.

Modifications to the engine-
First, I went through the entire motor and replaced all bearings, gaskets, oil pump, etc. All fresh and new "ish". The heads were re-manufacture stock from a reputable company. Just stock truck heads.... nothing special.
Running a Sloppy Stage 2 cam, springs, retainers, etc. and new lifters
Intake manifold is a Speedmaster unit (old style for ls1's) needed it to fit under the hood and not be made of plastic (I plan to go boost)
102mm Throttle body (sorry, I did this on the cheap... its a budget build but I used an Amazon unit.... hate if you want)

Wiring and Sensors
PSI wiring harness purchased through LOJ (they have the best fitting parts and have been doing this swap for a while)
LS3 MAP
5-pin style MAF (has IAT in it also) (I bought the part number they recommended but I know I can just run speed density and delete it, which I plan to do)
Cam and Crank sensors are new stock replacements
I don't have any knock sensors installed currently. I'm still trying to determine what setup I should use but they don't matter for starting purposes (meaning the engine will start without them)
Coolant Sensor was moved to the passenger side rear of the head and replaced with a new unit
Injectors are stock truck injectors currently (with a ton of miles on them but I cleaned them internally with a kit I bought) I also have a brand new set of Holly 100lbs/hr that I was planning to install when I go turbo.
Fuel rails are JEGS for LS1 style manifold and I am running a dead head system with a corvette fuel filter (58psi setup).


Car has full exhaust right now with stock replacement O2 sensors.

That's all I can think of at the moment. When I look at the log, I can see a couple of numbers that seem "off" to me (example: one of the channels monitors computer voltage... I noticed it was over 12v at the beginning and just above 10 by the end, then recovers once I stop cranking (full battery charged with a tender, not running the jumper pack at all when I did this) but I don't understand it well enough yet to confirm. Any help would be greatly appreciated!start up first log file still no start.hpl

Sorry, I wanted to add the actual tune file as well:

[5FDP]

I don't think your MAP data is right. You need to double check your linear and offset settings for the MAP sensor and put in the right data. The key on engine off in that log shows the MAP in the 40's, it should be near 100 if you live at sea level.

The data log shows a P0335 code for the crankshaft, it won't want to start with that.

Also, did you do a write entire when you did the OS upgrade? And why did you apply the 1 BAR speed density OS if you plan to boost it? You should have just put the stock tune into speed density instead of doing the OS upgrade.

[cm1wrx]

Thank you for the tip on the MAP. I will take a look. I am around 700ft sea level here I believe. Regarding P0335, that's one of the things I have been concerned with. I think the sensor might be bad. I have a replacement and will swap it in.
For the OS upgrade, I believe I did "write entire" but not 100%. Is there a way to verify? For the 1 bar, I actually had a 3 bar universal wired but was having the starting issue and thought I would just put a more stock style sensor in (LOJ recommended this one) to eliminate some of the "unknowns" from what I actually want vs what they offer (typically people stop at N/A with this setup but several have done turbo... its just a small space with a lot of plumbing, which usually involves tipping/relocating the radiator. Lots of fab work that I still have to do for this and I really want to drive the damn thing so N/A for now it is....). If I put the stock tune into speed density and resolve the P0335 issue, you think that will do it or is there anything else I should look for? The wiring harness threw me off a little as it has provisions for a few configurations ant that played a factor in my decision making as well and I wasn't even sure if I had enough to even start initially. This is also my first LS platform period so a lot of this is new to me. I knew what the factory nissan motor needed to start but not much on what the LS requires....

[gtstorey]

I would say put the tune back to stock and only change things as absolutely needed for sensor changes like map settings (and you really should be giving part numbers for the things changed, not just just "LS3 MAF", "1 Bar" or "stock"). Then disable VATS. Then treat it as a normal "No Start".

I would also get the wiring diagrams for the donor and confirm every wire lands where it should. The number of swap harnesses that come through here that are 100% right is pretty small.

Your Holley injectors aren't going to work very well when you get to that point since they likely don't have GM data.

And yes, you likely need a new battery.

And you through a lot of things on this at once so be prepared for a lot of trouble shooting. I would put as much hard parts back to stock as you can until you get it to run. Don't worry about clearance, just get it to run.

[Alvin]

Something is wrong with the map sensor.. Maybe wrong sensor used or prehaps a wiring issue. It should read around 100kPa and yours reads half of that. Check the PN of the map sensor you are using, double check the harness pin out.. aftermarket often has little errors like this. And if all that checks out try a new map sensor.

Also the crank sensor codes need to be addressed. That is a problem.

[cm1wrx]

Thank you everyone! Sorry for no part numbers. I know I threw a lot at this for starting and am prepared to do the necessary trouble shooting. I figured jumping right into this without purchasing a tune would be the best way to force myself to learn! Its a little more challenging than I expected but everything you guys are saying makes total sense. I am going to check the crank sensor wiring and replace the sensor. Then, I will put it back to the stock program (VATS removed) and re-scale the MAP. Will report back later today.

[gtstorey]

Adding things like a Chinese throttle body on top of everything else that could be wrong is asking for trouble. The best way to do a swap is to do the minimum required changes until you get it running again.

[cm1wrx]

I don't think your MAP data is right. You need to double check your linear and offset settings for the MAP sensor and put in the right data. The key on engine off in that log shows the MAP in the 40's, it should be near 100 if you live at sea level.

The data log shows a P0335 code for the crankshaft, it won't want to start with that.

Also, did you do a write entire when you did the OS upgrade? And why did you apply the 1 BAR speed density OS if you plan to boost it? You should have just put the stock tune into speed density instead of doing the OS upgrade.

I double checked the linear and offset settings for the MAP. They are correct at 93.43kPa and 10.33 (I know... its 10.34 but it keeps switching it back to 33). If that is correct and I am getting what I am getting (MAP in the 40's) what else should I be looking for? Still going to switch out the crank sensor and check the wiring there... now that I know not to trust harness manufacturers (thanks to the person that offered that!).

[cm1wrx]

Adding things like a Chinese throttle body on top of everything else that could be wrong is asking for trouble. The best way to do a swap is to do the minimum required changes until you get it running again.

I know... I know.... admittedly this is not the route I wanted to go but I got a little carried away. I had the manifold. It was cut for a 102 throttle body. I'm putting this together on a shoestring budget. It was the only manifold that fit and wasn't plastic. I probably should have bought something reputable but I don't know any of the "horror stories" of which ones are bad and which are good

[edcmat-l1]

What the heck is a speedmaster intake? And a 102 TB on that engine is useless.

[gtstorey]

What the heck is a speedmaster intake? And a 102 TB on that engine is useless.

https://www.speedmaster79.com/air-fu...ed-Small-Block

[gametech]

Don't be surprised if it does start that you then have a massive vacuum leak. Most of those china intakes that I have seen were fabbed up on a jig with the wrong angle for the intake flange to mate to the heads. One edge will be flush, and the other will be .120" high from the head surface. Thick o rings sometimes seal the difference, but not always.

[cm1wrx]

Don't be surprised if it does start that you then have a massive vacuum leak. Most of those china intakes that I have seen were fabbed up on a jig with the wrong angle for the intake flange to mate to the heads. One edge will be flush, and the other will be .120" high from the head surface. Thick o rings sometimes seal the difference, but not always.

Well, its not made in a jig, its actually a cast piece that is essentially a copy of the BBK unit from the early LS1 days. Its also not 0-ring style gaskets, its traditional style and felpro makes a set that work extremely well with these intakes... I kinda of already found the pitfalls but so far I am happy with the fitment. Take a look at Richard Holder's intake manifold comparison (with this intake) on youtube. Its has its "goods" and "bads" but it works for my application so I am good with it!

[5FDP]

I think the pin out for the MAP could be different from a LS1 style MAP to a LS3 style MAP. I think 2 pins have to be swapped around for the different in sensors or that MAP is just bad out of the box.

[gametech]

Picture of wiring difference.LS2-to-LS1-Picture-1.jpg

[cm1wrx]

I think the pin out for the MAP could be different from a LS1 style MAP to a LS3 style MAP. I think 2 pins have to be swapped around for the different in sensors or that MAP is just bad out of the box.

The wiring harness was set up to accept the LS3 style MAP, which I have installed and correctly scaled. I just swapped the crank sensor and checked the pin outs all the way to the ecu. Everything is correct for that and the sensor is working according to the test I just ran. Think low voltage is an issue here as well. Anyone have any experience with the symptoms of low voltage? I have it on a jumper right now and am letting it charge up a bit to give it another try. If it doesn't work or I find an issue with the battery I will replace it. Then, my next step will be to check the cam sensor circuit.

[gametech]

Did you verify your coil pack orientation? On a full rewire job it is very easy to flip them front to back so that 1-7 and 2-8 become 7-1 and 8-2.

[cm1wrx]

Did you verify your coil pack orientation? On a full rewire job it is very easy to flip them front to back so that 1-7 and 2-8 become 7-1 and 8-2.

Thank you! I wasn't sure about the coil wiring early on and I did check it already. Followed the "red on right" rule for the coil packs. The wiring is in the correct position.

Also, I just finished checking the MAP wiring and the Crank sensor wiring. From what I can tell, the Map sensor wiring and readouts are correct. I know people have said I should be closer to 100kpa but that's only with it running. I can't do that just yet. According to the "almost never wrong" internet" j/k.... I should see about 30 kpa with a stock cam. I have an aftermarket, stage 2 cam so that is apparently why my numbers are a little higher. I am creating more vacuum while cranking due to the larger cam. Or at least, I think I understand it this way....

The only things I really have left to look at are the battery (I hooked it up to the jumper for all of the test firing today. it cranks strong for a few seconds and then starts to fall off. I saw the control module dip down to 8.6 volts during cranking with the jumper off so I think there might be a bad cell) and the cam sensor wiring (back of the motor, with the intake in the way, so pain in the ass as everyone knows). I will put a new battery in tomorrow and give it another go. Otherwise its going to have to sit for a few days more as I have to travel for work.

[blindsquirrel]

No. Barometric pressure at sea level is 101 kPa, your MAP should be equal to baro at KOEO. When the engine starts and there is vacuum, MAP will be less than whatever it is at KOEO.

edit: Your KOEO MAP of 43 kPa is equal to an elevation of 21876.6 feet. If you are not actually located at 21876.6 feet then that reading is wrong. Being stuck perfectly flatlined at 43 kPa ALL THE TIME NO MATTER WHAT is a clue that it's not actually measuring anything, it's a wiring error.