5.3 swap in '90 Sub, Had it running, now no start!

[robster495]

Hey guys, so I just dropped a 5.3 into my 1990 Suburban, reworked the harness, followed about 15 different forums to the "T", and got that thing running! Running well too, like it would start right up and stay running. However, I saw I was misfiring a few and so I replaced all the injectors with brand new ones today. I started the motor, no misfires! Yay!

BUT.

After shutting it off I bolted the mani's back on, took me maybe 20 minutes, then I went to go start the motor again. No start. It's turning and turning, but wont fire.

Brand new injectors, all the coils work, brand new spark plugs work, I had this thing running with no issues whatsoever right before this. It even sat and ran for 15-20 minutes so I could test cooling and all that jazz at operating temp. I'm stumped. I followed y5 a lot on this, and Russell. If anyone has input, please let me know. Grounds are there, only pcm code thrown was me having the maf unplugged, but that's it. I'm this close to finishing this thing. TIA.

 

[K30Blazer]

Pull the tps sensor and plug it back in. Disconnect the battery etc. that is where I would start and see what codes you get. Is the maf plugged in yet?

 

[robster495]

Pull the tps sensor and plug it back in. Disconnect the battery etc. that is where I would start and see what codes you get. Is the maf plugged in yet?

Thanks for chiming in! I'll have to get to all that in the morning, late night shifter here. I did plug the maf back in as my last attempt today, but no dice. Maybe it'll help when I unplug/plug the battery. What does pulling tps do?

 

[K30Blazer]

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Thanks for chiming in! I'll have to get to all that in the morning, late night shifter here. I did plug the maf back in as my last attempt today, but no dice. Maybe it'll help when I unplug/plug the battery. What does pulling tps do?

When I first installed my ls the tps was giving me a bunch of starting issues. It controlled the fuel flow and I could not get the truck to start or run without resetting it.

Sounds like a sensor off.

 

[Russell]

Sounds like a ground didn't get hooked back up or something got pinched somewhere. The easiest way to troubleshoot this will be to go through the PCM connectors one at a time and check all of the power inputs and grounds are good, then check for power and ground at the coil pack connectors and finally for power at the injector connectors.

Have you verified that you have spark? Does your check engine light turn on with the ignition in the on position?

 

[robster495]

Sounds like a ground didn't get hooked back up or something got pinched somewhere. The easiest way to troubleshoot this will be to go through the PCM connectors one at a time and check all of the power inputs and grounds are good, then check for power and ground at the coil pack connectors and finally for power at the injector connectors.

Have you verified that you have spark? Does your check engine light turn on with the ignition in the on position?

Pretty darn sure I have spark, the motor was firing on all cylinders no problem for about 3 minutes, this being 20 minutes prior to the starting fail. I'm leaning in the resetting (of something I guess) direction, because I had this problem before but it never lasted this long. When I was having those issues I just thought I was low on gas, I never had the battery committed to being plugged in until this week.

Today I must've forgotten, but I did get it to start with the exhaust back on, that's when I had it running for a few minutes.

 

[Russell]

Pretty darn sure I have spark, the motor was firing on all cylinders no problem for about 3 minutes, this being 20 minutes prior to the starting fail. I'm leaning in the resetting (of something I guess) direction, because I had this problem before but it never lasted this long. When I was having those issues I just thought I was low on gas, I never had the battery committed to being plugged in until this week.

Today I must've forgotten, but I did get it to start with the exhaust back on, that's when I had it running for a few minutes.

Best thing to do is start with the basics. There isn't really anything to reset on these engines. They either work or they don't. You need 3 things to make the engine run - Fuel, Air and Spark. Check to make sure you've got all three and go from there. The air is kind of a given

 

[diesel4me]

Cant forget timing!......

 

[robster495]

hey guys! Made it to the garage (dang it's getting chilly in MD!)

I unplugged the negative side of the battery for 1 minute, plugged it back. And the damn thing started up! Now I'm nervous though.

I'm currently letting it run for a good bit to let it warm up and I'm gunna scan. Russell: I don't have the CELight itself wired, but I have the obd2 port (temporarily) wired up. It's reading:

P0118 ECT Sensor Circuit high voltage
P0102 MAF sensor circuit low frequency

I've plugged the MAF in, but I'm using the original engine temp sender from the suburban itself. Would that code throw anything off to keep it from startingredients?

It's literally running right now, sounds good, but I'm afraid once I shut it off again it won't start back up without the battery game I just played. Thoughts??


EDIT: I shut it off to clear the codes, but alas, not starting again. I did the battery dance but still no luck..

 

[Russell]

Do you still have the original engine coolant temp sensor on the LS as well? Engine coolant temp is a very important input.

 

[robster495]

Do you still have the original engine coolant temp sensor on the LS as well? Engine coolant temp is a very important input.

I don't. It was broken when he gave me the motor. But I should be able to get one down the road. However I'm using an adapter to use my original one in its place on the block. Should I try to route an LS ECT Sensor somewhere else on the block?

 

[K30Blazer]

where is your MAF in relation to your throttle body? I know if they are too far away they can cause issues. But generally not starting issues. Mine was doing a strange thing where it would run fine and next time I would start it, the idle would be all over the place. I would pull the TPS and it would fix it. Did this several times and the issue resolved itself.

I have learned maybe incorrectly that these engines seem to have a memory. I coasted down a 5 mile grade in neutral about a month or so before the idle issues showed up. I have since learned that neutral coasting is not a good idea. Not sure if that caused any issues with my TPS but it was suspicious.

I also had a knock code that ended up being a bad MAF. It wasn't throwing a MAF code, but under full throttle would always throw a knock. Josh at Team 208 traced it to the MAF for me. Guy is genius.

You have a sensor issue going on. Even if you have fuel, spark and air if the PCM is reading otherwise it can mess with things.

Will it turn over?

 

[robster495]

where is your MAF in relation to your throttle body? I know if they are too far away they can cause issues. But generally not starting issues. Mine was doing a strange thing where it would run fine and next time I would start it, the idle would be all over the place. I would pull the TPS and it would fix it. Did this several times and the issue resolved itself.

I have learned maybe incorrectly that these engines seem to have a memory. I coasted down a 5 mile grade in neutral about a month or so before the idle issues showed up. I have since learned that neutral coasting is not a good idea. Not sure if that caused any issues with my TPS but it was suspicious.

I also had a knock code that ended up being a bad MAF. It wasn't throwing a MAF code, but under full throttle would always throw a knock. Josh at Team 208 traced it to the MAF for me. Guy is genius.

You have a sensor issue going on. Even if you have fuel, spark and air if the PCM is reading otherwise it can mess with things.

Will it turn over?

Interesting post, thanks for the info. More I learn the better! As for turning, it'll turn and turn and turn. I think I've killed my battery (hooray for warranties lol), but yes it turns, just doesn't want to fire for some reason.

I had to leave the garage, it's so bitter cold due to high winds today, my fingers were about to fall off. So I went home to research.

The MAF is no further away than its usual stock distance. I measured it out to actually be one inch closer than stock. I also cleaned it thoroughly and delicately.

In terms of pulling the tps connector, should I try to start it with it pulled?? Or just unplug/plug back in?

 

[Russell]

You need to buy an adapter to install your original coolant temperature sensor for your gauge in the opposite head and replace the temp sensor for the PCM. That'll cause all kinds of issues not having one in place.

You may also have some MAF issues as well. Could be dirty, or the wrong MAF for the application. Either one of these sensors can cause a no start condition.

 

[robster495]

You need to buy an adapter to install your original coolant temperature sensor for your gauge in the opposite head and replace the temp sensor for the PCM. That'll cause all kinds of issues not having one in place.

You may also have some MAF issues as well. Could be dirty, or the wrong MAF for the application. Either one of these sensors can cause a no start condition.

Interesting!! Okay got it. Put my suburban temp sender in the opposite head, and replace original ECT where it ought to be.

I'll get looking for adapters asap. I will need a junkyard run though. The pigtail was included in the damaging of the LS ECT Sensor, luckily enough wire remains. Simple solder job, phew.

Do you know of any likely spots I can put the suburbans temp sender? The heads are identical so it should simply be opposite, right?

In any case this is all good to know, thanks guys! I will report back asap. I only have mornings to work (no electricity in the garage >_< )

Edit: Russell, could you expand on the possibility of an incorrect MAF for the app?

 

[Russell]

If the engine / tune are stock and it is reporting a frequency issue, it could be a faulty or incorrect MAF for your application. You may have damaged it while cleaning it as well? They are kind of delicate. You need to check the frequency of the MAF and compare it to your expected CFM of air at that given RPM. If it's off, it'll cause lots of issues.

 

[K30Blazer]

If the engine / tune are stock and it is reporting a frequency issue, it could be a faulty or incorrect MAF for your application. You may have damaged it while cleaning it as well? They are kind of delicate. You need to check the frequency of the MAF and compare it to your expected CFM of air at that given RPM. If it's off, it'll cause lots of issues.

Try de pinning the yellow wire going to the MAF and see if it makes any difference. Long shot here, but I saw this once. You got all the theft stuff removed from the PCM? I know if the skm chip in the key isn't recognized in a stock application it will turn over but not start. Doubt this is the issue but.....

for the TPS just unplug it spray some electrical parts cleaner or MAF cleaner in it and put it back on.

 

[robster495]

Try de pinning the yellow wire going to the MAF and see if it makes any difference. Long shot here, but I saw this once. You got all the theft stuff removed from the PCM? I know if the skm chip in the key isn't recognized in a stock application it will turn over but not start. Doubt this is the issue but.....

for the TPS just unplug it spray some electrical parts cleaner or MAF cleaner in it and put it back on.

Does depinning matter on which end? I'll give that a shot tomorrow! Thanks for a possible lead, I'll report back.

As another general question, since it seems to be pcm/sensor issue, would getting dropped off at a dyno tuning shop help find the issue?? There's a reputable one near me.

 

[robster495]

Does depinning matter on which end? I'll give that a shot tomorrow! Thanks for a possible lead, I'll report back.

As another general question, since it seems to be pcm/sensor issue, would getting dropped off at a dyno tuning shop help find the issue?? There's a reputable one near me.

Hey guys, at the garage now. So weird, I pulled the connector off the MAF because I noticed three wires werent fully pinned in. Before I poked them back in, I went to turn the motor, and it started on the second turn!

I went to the reader and saw I still had some codes so I shut it off to get em cleared and to see what would happen if I plugged the MAF back in with those wires repinned correctly...started right up!

So I shut it off again, and waited about 15 minutes and he started up without fail. So things might be looking up. The codes I have now are

P0650 MIL Control
P0118 ECT Circuit high voltage

Russell, I found the port in the opposite head where I can place an original LS ECT Sensor. I will be going to the junkyard when it's not freezing here (so much ice!)

I will update when the ECT Sensor is in. Thanks guys! Any other tips are welcome, almost finished!

 

[robster495]

If the engine / tune are stock and it is reporting a frequency issue, it could be a faulty or incorrect MAF for your application. You may have damaged it while cleaning it as well? They are kind of delicate. You need to check the frequency of the MAF and compare it to your expected CFM of air at that given RPM. If it's off, it'll cause lots of issues.

I now am having some TCC questions after having had a quick conversation with my PCM programmer. Apparently I'm wiring it wrong, I noticed when I had the motor running, my 700r4 wasn't engaging any of the gears. Any insight?