350 vortec 5.7 lower intake leaking vacuum?? Help please

[squaredeal91]

I have a 99 suburban 350 vortec. It's our main driver and pretty much only thing my wife drives. It's been down since yesterday morning and I'm thinking its the lower intake leaking because there is a fair amount of oil under upper intake with the spider unit. I'll get pics. So to back up to last week it was intermittently running rough. Seemingly to be till it warmed up sometimes. But mostly in the morning. And in a parking lot it wouldn't move and backfired and died, barely got it started to park. I unpluged coolant temp sensor and it ran well enough to get home running surprisingly ok but idling low/labored.
for the last few months I noticed that if it sat for a complete day on the weekends it didn't like to start. It sat on sunday and Monday and wouldn't start Tuesday morning. Acts like it will sometimes but goes wher like it's vapor locking or like a carb engine would do when timing is advanced. Fuel pressure is around 60 when cranking wich should be adequate. I'm at this point hoping it's a bad lower intake manifold gasket so I can fix it and get back to my work. I'm also suspicious of the spider unit itself too. Any ideas is appreciated.

 

[squaredeal91]

Looks like front end is darker and drier and the rear by distributor is cleaner and more oily. I think its more than gravity. Also fresh looking oil on the gasket surface on back /side in last photo.

 

[squaredeal91]

Forgot to mention I have confirmed spark getting to distributor and out of distributor to plugs. I checked plug gap also. Was at .60 wich is normal.

 

[bucket]

I think you may have two issues going on. Leaking intake gaskets and also a spider injector that needs updated to the new style that gets rid of the poppet valves.

How many miles on it? Intake gaskets ever done on it? If so, who did it and were the steel core gaskets used, or the original type plastic?

 

[squaredeal91]

I think you may have two issues going on. Leaking intake gaskets and also a spider injector that needs updated to the new style that gets rid of the poppet valves.

How many miles on it? Intake gaskets ever done on it? If so, who did it and were the steel core gaskets used, or the original type plastic?

I think you're correct about two problems going on. Approximately 180k on it. I changed intake gaskets 6 years ago. I'm sure Fel-pro but I think they were plastic. They will be off tomorrow morning to see.

 

[squaredeal91]

I've got gaskets at the parts house waiting. But I don't yet know what there made out of. I'll be picking them up tomorrow and I think I'll have to bite it and order a new spider unit in the morning if i can. I really wanted a good name brand unit but there way out of my reach. Anything new should be an improvement at least. It's an original spider in it. I do have another used one of unknown condition.

 

[CalSgt]

@bucket seems spot on…

Be sure to order the upgraded lower intake gasket set, the factory style is plastic and the upgrade is aluminum. The aluminum ones are over twice the cost, I think I paid over $50 for my last set. I also bought ARP bolts since the GM ones are supposedly one time use.

The upper intake is darker and dryer at the front of the engine because that is where the EGR feeds in. EGR is part of the reason it’s so gross in there to start with.

IIRC the injectors have a check valve that keeps them from leaking raw fuel into the intake runner when the engine is shut off. They leak when dirty. Not sure if that explains the hard starts.


Sometimes those poppet style spiders can be freshened up.

Started by scrubbing the nozzles with some gas and injector cleaner and a toothbrush.

On a bench we used a bucket with some fresh fuel and a high concentration of injector cleaner

Hooked a hose up to the inlet and another for a return

hot wired a fuel pump in the bucket

triggered the injectors with 12 volt jumper wires.

We cycled through the injectors and looked at their spray patterns. Most of the spray patterns cleared up by cycling them repeatedly. During operation they only spray for a fraction of a second each time, running them for several seconds really cleans them out.

Out of 3 spider assemblies I was able to get 1 working great, 1 was okay, and the third had nozzles that would not clear up.

ETA: IIRC we hooked a pressure gage on the system, one of the regulators was bad and was driving pressure way up. I think we checked to see how long the system held pressure after the pump was shut off too.

 

[CalSgt]

Did you feel or smell the puddle of oil in the one intake runner?

Just curious if it was a puddle of gas and not oil.

 

[squaredeal91]

@bucket seems spot on…

Be sure to order the upgraded lower intake gasket set, the factory style is plastic and the upgrade is aluminum. The aluminum ones are over twice the cost, I think I paid over $50 for my last set. I also bought ARP bolts since the GM ones are supposedly one time use.

The upper intake is darker and dryer at the front of the engine because that is where the EGR feeds in. EGR is part of the reason it’s so gross in there to start with.

IIRC the injectors have a check valve that keeps them from leaking raw fuel into the intake runner when the engine is shut off. They leak when dirty. Not sure if that explains the hard starts.


Sometimes those poppet style spiders can be freshened up.

Started by scrubbing the nozzles with some gas and injector cleaner and a toothbrush.

On a bench we used a bucket with some fresh fuel and a high concentration of injector cleaner

Hooked a hose up to the inlet and another for a return

hot wired a fuel pump in the bucket

triggered the injectors with 12 volt jumper wires.

We cycled through the injectors and looked at their spray patterns. Most of the spray patterns cleared up by cycling them repeatedly. During operation they only spray for a fraction of a second each time, running them for several seconds really cleans them out.

Out of 3 spider assemblies I was able to get 1 working great, 1 was okay, and the third had nozzles that would not clear up.

ETA: IIRC we hooked a pressure gage on the system, one of the regulators was bad and was driving pressure way up. I think we checked to see how long the system held pressure after the pump was shut off too.

It holds pressure to a degree. Shortly after pump cycles it will be closer to 50 psi. I will find it at 30-40 psi ,15 minutes later. I like your idea of cleaning it out with injector cleaner.

 

[squaredeal91]

Did you feel or smell the puddle of oil in the one intake runner?

Just curious if it was a puddle of gas and not oil.

I didn't feel the puddle tho now I wish I did. I thought it was oil but it could be either.

 

[RanchWelder]

Here's your intake set with Steel Mani Gaskets with thr Nitrile Rubber surrounds.
This might be what CalSgt is speaking about.

These are known to seal much better, especially on Edelbrock manifold conversions.
It comes with stuff you might want for your engine to seal up, like it or not.

Fel-Pro Intake Manifold Gaskets MIK98000T​

https://www.summitracing.com/parts/fel-mik98000t/make/chevrolet

You must be registered for see images attach

There is no way to buy the metal gaskets seperately.
Vic Heinz became Mahle and started selling both sets, the $29 set and the $36 set, using the exact same plastic.
The picture they use for the more expensive set is WRONG. EVERYWHERE.

Contacting the Alabama support team resulted in them contacting engineering.
The nice lady emailed me, she was hung up on, asking "why the incorrect photo's on every web site in the USA?".

Buy the part number listed and return anything plastic, if you want to prevent cylinder #7 from burning up the plastic version gasket near the oil sending unit sensor on the back chinarail. Or use it and plan on changing it out every 25K miles.

There are way too many pictures of the plastic intake gaskets failing on the web.
There is no info on how long it takes or what seems to be the consistant cause of the same port failing and leaking.
You might be seeing fuel and/or water, if it leaked near the driver's side water port.
When the gasket leaks air it sounds like an alternator belt squealing.
Very tough to figure out the first time.

Asked Mahle to consider breaking out the steel stamp dies and please start re-manufacturing them for us. Crickets...

Heard of a thicker paper gasket for the OEM manifold, sold by Fel-Pro working too.
However, since my engine used the EDL Mani, did not document that part number.

Maybe somebody else has it, if you do not want to shell out for the set above and use the thicker paper set.

 

[squaredeal91]

Here's your intake set with Steel Mani Gaskets with thr Nitrile Rubber surrounds.
This might be what CalSgt is speaking about.

These are known to seal much better, especially on Edelbrock manifold conversions.
It comes with stuff you might want for your engine to seal up, like it or not.

Fel-Pro Intake Manifold Gaskets MIK98000T​

https://www.summitracing.com/parts/fel-mik98000t/make/chevrolet

You must be registered for see images attach

There is no way to buy the metal gaskets seperately.
Vic Heinz became Mahle and started selling both sets, the $29 set and the $36 set, using the exact same plastic.
The picture they use for the more expensive set is WRONG. EVERYWHERE.

Contacting the Alabama support team resulted in them contacting engineering.
The nice lady emailed me, she was hung up on, asking "why the incorrect photo's on ever web site in the USA?".

Buy the part number listed and return anything plastic, if you want to prevent cylinder #7 from burning up the plastic version gasket near the oil sending unit sensor on the back chinarail. Or use it and plan on changing it out every 25K miles.

There are way too many pictures of the plastic intake gaskets failing on the web.
There is no info on how long it takes or what seems to be the consistant cause of the same port failing and leaking.
You might be seeing fuel and/or water, if it leaked near the driver's side water port.
When the gasket leaks air it sounds like an alternator belt squealing.
Very tough to figure out the first time.

Asked Mahle to consider breaking out the steel stamp dies and please start re-manufacturing them for us. Crickets...

Heard of a thicker paper gasket for the OEM manifold, sold by Fel-Pro working too.
However, since my engine used the EDL Mani, did not document that part number.

Maybe somebody else has it, if you do not want to shell out for the set above and use the thicker paper set.

I'll check part numbers before I open it so I can be sure to get the right ones.

 

[squaredeal91]

Did you feel or smell the puddle of oil in the one intake runner?

Just curious if it was a puddle of gas and not oil.

I checked out the puddle. Feels like oil because of what it's in but smelled more like fuel maybe. I did use a little gas to clean the throttle body and maybe it's from that.

 

[squaredeal91]

Oil by distributor but not coming from it by the looks of it. I'm thinking maybe from rear upper intake possibly because it'd more dry up by the lower intake bolts.

 

[squaredeal91]

@CalSgt & @RanchWelder I declined the first set I called on and ordered the one with the part number you gave. It's close to double the cost but is worth it to me. I'm also trying to order a new updated spider today if I can swing it.