Hot Stalls After Header Install

[1985K5Blazer305]

Hey guys, I recently added long tube headers to my stock 1985 K5 Blazer 305 (LE9 maybe) and a 2.5" dual exhaust with no cats. Upon starting, the car idles great and drives unaffected (apart from a great sound) However, after 4 miles or so of harder driving it putters out and dies. My two lines of thought are that the 2.5s w/ duals aren't supplying enough "back pressure" if you'll call it, but why only after short driving. Note that engine temps are normal with the headers but engine bay temps are higher than before. My second thought is that this increased bay temp is affecting the fuel lines and pump and causing them to vaporize earlier of something of that sort. Any insight is much appreciated as my knowledge is amateur on this subject. Thanks

 

[nvrenuf]

I’d look at exhaust vs fuel line routing for opportunities for vapor lock.

Technically, exhaust back pressure could effect power but in most cases an indiscernible amount (unless the exhaust is plugged).

 

[Wes Harden]

Welcome @1985K5Blazer305

Yes it is possible that the new exhaust is boiling the fuel in the lines. The lines run down the inside right frame. Long tube headers usually have the collector near the front springs rear shackle, which is very close to the fuel lines. Also where the exhaust pipe squeezes past the T case is very close to the fuel lines. Heat barrier wrap will help, needed every ware the exhaust is close to lines. Might want to heat wrap your starter motor too, the heat from headers will effect it too.

 

[1985K5Blazer305]

Update: Took a bunch of test drives and monitored fuel line temps, didn't have any issues and the car ran fine even under long strenuous drives. I'm going to install a couple heat shields around where the lines get close to the headers but I supposed the issue solved itself or just needed to settle in. Thanks for the input

 

[HawK5]

Def wrap you starter, you can get a cut to fit blanket of heat shield at Napa for $30-40. The heat will kill your starter and leave you stranded. It’s happened to me on multiple vehicle. I just put headers on my 80 Jimmy last week and wrapped the starter as part of the install. There’s enough left over to wrap fuel lines and power cables as needed.

 

[4X4ForDad]

What was said above is true. If you go to start the vehicle and the starter drags or just clicks it could be not enough voltage getting to the solenoid because of old wiring resistance and/or heat soak.

Get a Ford type starter solenoid and wire in line with the GM solenoid wire, usually 10 ga purple going to the starter. Install one large terminal to the battery, other side to the ppl wire to the starter and the ppl wire from the key switch to the exciter terminal on the new solenoid.

Also, if your starter has one copper strap connection from the solenoid that is a "standard starter" A heavy duty starter has 2 copper straps going into the starter housing. These are usually found on the Big Blocks.

I hope this helps somebody.

 

[Wes Harden]

Just a bit more info on the dual solenoid @4X4ForDad mentioned. This doesn't work on starters with permanent magnets, or the modern mini starters.
Since I use the old style HD the dual solenoid method is how mine currently wired. No headers though.

 

[Blue85]

Get a Ford type starter solenoid and wire in line with the GM solenoid wire, usually 10 ga purple going to the starter. Install one large terminal to the battery, other side to the ppl wire to the starter and the ppl wire from the key switch to the exciter terminal on the new solenoid.

Just a bit more info on the dual solenoid @4X4ForDad mentioned. This doesn't work on starters with permanent magnets, or the modern mini starters.
Since I use the old style HD the dual solenoid method is how mine currently wired. No headers though.

I believe @4X4ForDad is describing the correct way to wire the solenoid. This maximizes the starting power and clearly works with PM starters. If it doesn't work, the starter-mounted solenoid is bad - but this gets a lot more life out of them.

https://ck5.com/forums/threads/tell-me-about-mini-starters.346246/

 

[Wes Harden]

Yes, there are 2 ways to do the remote solenoid mod. I haven't proved the above diagram will work with a perm magnet starter, I don't see why it wouldn't.
My method will not work with a perm magnet starter.
I have used both methods and the above diagrammed method I still the occasional no crank issue. My current wiring looks like this

factory left My system on right.

 

[Blue85]

But it's not always going to work. It creates a race condition where the starter can spin before the gear is engaged and prevent it from meshing with the flexplate. That method is for the Ford-style starter where the spinning of the motor extends the bendix, not the Chevy style where the solenoid throws it out.

 

[Wes Harden]

Are you talking about my method. If so, I need further explanation.
The solenoid activation also powers the cranking motor. I don't see how supplying the power this way changes that

 

[Blue85]

 

[Wes Harden]

yep motor doesn't turn till drive is extended. I am still missing the part where drive will spin before engaging the flex/fly wheel

 

[Blue85]

Oh, your purple jumper wire is between the S and the B. Then the timing will be correct. However, the voltage will be reduced since it's passing through both sets of contacts.

 

[Wes Harden]

Yes the 2 solenoids could cause reduced voltage, and after many years of service I would expect some voltage drop. Good heavy gauge cables and clean connections are always a must. The purple jumper lead is 10 ga so plenty of current to activate the dive solenoid

There is only the 1 large cable routed to the starter.

 

[Blue85]

I have used both methods and the above diagrammed method I still the occasional no crank issue.

But why would it? The cable from the battery to the starter?

 

[Wes Harden]

My thought was the 1st solenoid signaling the starter via the smaller gauge couldn't carry the current a hot starter solenoid needed. I am used the same components, for both versions. Cables, solenoid and starter. The jumper at the starter method has been through 3 Havasu summers, never failed to crank.