Pop, and boost spike under acceleration

VADER

Little engine that could
So, I finally got the car going after changing gas tank, fix fuel line in tank, mini starter (sounds weird vs orig), new front tires and battery. And a fuel filter
Take it out, seems to run fine but any slightly decent amount of throttle causes a pop and spike in boost. The spike is basically from being at -1 to 0 psi under throttle to a pop and spike in psi to 5 and then I let off. So, it's not under heavy throttle, I was thinking a hose is lifting up or a leak in lines.
I did a search and most think coil pack or module, plug wires.
Just wanted some thoughts before I start spending more $$. It did start to do this before I got everything replaced, but normally its floor it and boost slams to 20 psi plus.
Any thoughts, many things were replaced about 15 years ago but car has only seen maybe 2k miles in that time
 

Mr.Spool

Well-Known Member
So, I finally got the car going after changing gas tank, fix fuel line in tank, mini starter (sounds weird vs orig), new front tires and battery. And a fuel filter
Take it out, seems to run fine but any slightly decent amount of throttle causes a pop and spike in boost. The spike is basically from being at -1 to 0 psi under throttle to a pop and spike in psi to 5 and then I let off. So, it's not under heavy throttle, I was thinking a hose is lifting up or a leak in lines.
I did a search and most think coil pack or module, plug wires.
Just wanted some thoughts before I start spending more $$. It did start to do this before I got everything replaced, but normally its floor it and boost slams to 20 psi plus.
Any thoughts, many things were replaced about 15 years ago but car has only seen maybe 2k miles in that time
verify fuel pressure rise 1to1,and no hoses that are unclamped,ripped,and vac lines are secured.
 

VADER

Little engine that could
Got to take the car out today, same result. So, the car basically will pop and boost spike to around 3 psi when there is any attempt to go over 0 psi and then go back down and would keep popping until I give up. I checked the lines, nothing obvious for a leak but I would towards something larger rather than 1 small vacuum line.
If this causes a small spike in boost, I guess I am trying to figure out where I should be focused. Waste gate lines? The boost line feeds off the vacuum block so if reaches there but escapes. Im stumped right now
 

NY Twin Turbo

All the good stuff.....Times 2.
Got to take the car out today, same result. So, the car basically will pop and boost spike to around 3 psi when there is any attempt to go over 0 psi and then go back down and would keep popping until I give up. I checked the lines, nothing obvious for a leak but I would towards something larger rather than 1 small vacuum line.
If this causes a small spike in boost, I guess I am trying to figure out where I should be focused. Waste gate lines? The boost line feeds off the vacuum block so if reaches there but escapes. Im stumped right now
Check the plug wires real good.
 

No disintegrations

Well-Known Member
Sounds to me like it's backfiring through the intake. The pressure is shown on the boost gauge but its not boost. It's just an explosion. Most engines that pop through the intake are lean. However on these cars most people seem to find bad coil pack or module can cause this too. Can't hurt to borrow known good ones.
 

TexasT

Texas, Where are you from
When you say "spike" and the boost maxes out at 3psi is this what you are saying? Are you using the stock hose couplers on the turbo to intercooler and ic to up pipe, and up pipe to tb?

I think you have a coupler "blow out" and they need to be upgraded to better units. The pop is the coupler letting the boost out IMO.
 

VADER

Little engine that could
This is under mild acceleration, just at the point of keeping the car at 0 boost, it tends to pop, boost spikes slightly. I have the max effort, so no maf. Most of the hose clamps are heavy duty, but they shouldn't lift at this level regardless. It's almost like a hose is torn and pops under pressure but then boost would not increase at all since the gauge reads off the throttle body.
 

NY Twin Turbo

All the good stuff.....Times 2.
Power brake the car to 1-2 pounds of boost in a very dark place. Have someone stand along side the fender and look under to see if they see a lightning show around the headers. Try it again with light. Check with soap/water spray bottle for bubbles at hose connections. Don't spend too much time on these little tests. It's easy to do so it's worth giving it a whirl. But move on to other recommended procedures to explore other possibilities.
 

VADER

Little engine that could
Bringing to the top so I can find it. Checked coil packs, and all read 11.7-11-9 in the 20k test limit.
 

VADER

Little engine that could
Pulled driver side plugs, ngks gapped around .25 or so. Plug wire connection to plug was corroded with soot on porcelain, so I cleaned with deoxit and added dielectric grease between.
anyone know the resistance on stock plug wires? I checked but forgot and will check again. One wire seemed to jump around but the wires them selves looked good.
Will check pass plugs soon.
 

Chuck Leeper

Toxic old bastard
Staff member
Plug wire connection to plug was corroded with soot on porcelain,
Either the plug is leaking, or the header is blowing soot on it.
Also, look at the coil towers. See any carbon tracking?
Stock plug wires? As in original?
 

VADER

Little engine that could
the coil is clean, the wires are stock but not original. They might need replacing, not sure yet. Could it be soot from poor connection under plug boot? They were pretty bad. Header leak I think I would hear it but under throttle it’s possible. Thanks chuck!
 

Anthony P

sharing knowledge with those who care to listen
Bringing to the top so I can find it. Checked coil packs, and all read 11.7-11-9 in the 20k test limit.
I wish GM never published STATIC resistance values in the service manual. A coil can appear as OK with an ohm meter, but have weak spark or no spark under load at some rpm value and beyond. Casper's makes a coilpak/ignition module tester/simulator - PART # 102020. it's a great diagnostic tool to have or borrow. while I don't believe this is the cause of your issue, wanted to point out anyway. Couldn't find it on Casper's website, but it's on Jegs. you'll get a better price calling Casper's directly - 970.776.8740.

what you're describing as boost spike mirrors a failing factory wastegate solenoid. Your sig shows mods including a MaxEffort for fuel management & JT chip, but what are you using for boost control? manual boost controller? or factory ecm plus chip to achieve 25 psig. perhaps something to look at.
 

VADER

Little engine that could
The Jim testa chip is old and not used. I have the factory wastegate with an rjc manual control. It’s been a while, I’m pretty sure that’s it though.
im going to clean the other plugs and report back.
 

VADER

Little engine that could
Cleaned all plugs which were bad. Went for drive today, same symptoms. So, it’s more than likely the coil, module or wires. I don’t know much about the TR6 ignition, but it seems like a good alternative, rather than guessing until I find it.
 

scgnx2

Active Member
Did you take the ignition module apart from the coil pack and look at it ? If the epoxy encasing the module is soft or melted there’s a good chance the module is failing.
Also, look at the female connector that can connects to the module. The white wire which is on the end of the connector controls timing. If the contact is “deformed” or corroded it will have intermittent signal and your ignition timing will go wild. Which will cause pops or backfires.
I replaced my ccci connector for this exact same problem.
These connectors are like 35 years old and were never intended or designed to last this long. Casper’s makes a nice pigtail replacement for that. The TR6 is definitely the way to go if your ignition module/coil pack is bad. The costs for stock replacements are so expensive now. Cost wise it just makes sense to switch over.
 
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