Turbo Dodge Forums banner

1 - 17 of 17 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1
Hello everyone, I'm new here at the forums and need help diagnosing a no spark issue with my '86 GTS.

Here's my situation: I bought the car from a co-worker as a project car last October. The car was completely stock and ran alright. I took it upon myself to convert it from fuel injection to carb because it's something I've been wanting to do for a while now.

I'm using a Predator carb with a brand new fuel cell and fuel line along with a brand new external fuel pump. I wired the pump into the factory fuel pump connection under the rear of the car and it comes on like it should with the key. I've got my regulator set at 6.5psi and it holds no problem.

My issue is not getting spark. I'm using a MSD 6BTM box that I currently have disconnected, thinking it may be causing some issues, but not sure, so I've got the factory wires hooked up to the coil, which is brand new. The dizzy rotates when the engine is cranked over so I've eliminated a broken timing belt. I was thinking that the ASD was bad but if it was my fuel pump should not kick on when the key is turned, correct?

I've also tried running a hot wire directly from the pos side of the battery to the pos side of the coil but had no luck in producing spark.

I've read through tons of forums and all the info I can come across but nothing I have tried will light the engine up. At this point I'm considering trying to bypass the entire ASD/ stock ignition system. I'm wondering if there are certain connectors that the computer is trying to read from that are no longer active due to converting to carb.

All help is appreciated, thank you!
 

·
Super Moderator
Joined
·
11,698 Posts
so you went from efi to carb but you still have the efi computer and wiring harness ..?

I think that may be your problem right there

carbed mopars didn't have the LM/PM or smec system
they have a spark control computer - that looks EXACTLY like the power module beside the battery with the single exception of the vacuum diagram on the top
- which is only for the "fuel pacer" light on the dash - meaning good or not so good fuel usage

I'd think the wiring for that carb style spark control computer has to be much different too
 

·
Administrator
Joined
·
24,269 Posts
so you went from efi to carb but you still have the efi computer and wiring harness ..?

I think that may be your problem right there

carbed mopars didn't have the LM/PM or smec system
they have a spark control computer - that looks EXACTLY like the power module beside the battery with the single exception of the vacuum diagram on the top
- which is only for the "fuel pacer" light on the dash - meaning good or not so good fuel usage

I'd think the wiring for that carb style spark control computer has to be much different too
He stated he had an MSD system hooked up but disconnected that and still has the same "No Spark" issue.
Either way the criteria for "spark" is the same...

Constant 12 volts to the + Coil, Switching of the - Coil, Amperage Flow from the the Coil Secondary to the Distributor Cap, From Cap to Rotor, Rotor to Cylinder Terminal, Cylinder Terminal through Wire to Spark Plug.

Diagnostics regardless of the system will tell us what is missing and then we can figure out why.
 

·
Super Moderator
Joined
·
11,698 Posts
I know one thing that stops spark in an 86 efi turbo car , not having the fuel rail grounded to the firewall

sooo, IF we no longer have a fuel injector circuit from ECU through injector to ground .. and the computer senses that
..maybe power to spark gets turned , "not on"

'cause that's what happens when the ground strap between the fuel rail and firewall breaks in an old log turbo car (84-6/7) - I'd not be surprised if the same applies to TBI
of the same generation

if by process of conversion to carb , "this" happened it would explain very quickly , no spark
but brings the question
do I burn up the computer if I connect the fuel injector power lead to ground without an injector on/off/on/off action in between ?

'cause THAT might be what we call a short to ground (??)
 

·
Super Moderator
Joined
·
11,698 Posts
the question I have to ask is where on god's green earth did you find a predator carb , still worth using , and how just how big is it ?

a pic would really awesome !!
 

·
Registered
Joined
·
7 Posts
Discussion Starter #8
I apologize in advance for my ignorance as I'm more of a "wrencher" than I am an electronics guy.

I went through the step-by-step in my Haynes manual last night checking for continuity and power on different connections and found that the coil (brand new) is getting power but the dizzy is not firing the plugs. I pulled the dizzy this morning for further inspection and found that the rotor appears to be in corroded condition as well as the ends of the plug wires that poke through dizzy cap. I have a new dizzy, cap, rotor, and plug wires on the way now. If anything at least those parts will be new.

As was stated above, I also had the thought that I had disconnected a ground wire that needed to be grounded. Could I get away with grounding the fuel rail connection right off the connector or is there more to it than that?
 

·
Super Moderator
Joined
·
11,698 Posts
Its all mute until he runs diagnostics...
Until that we just wait...
and a buddy to hold the injector + to ground long enough to check for spark again
--FIRST test right there lol

maybe get lucky and run the short diagnostics list ..

if it ran before always always look at the project as the cause
 

·
Super Moderator
Joined
·
11,698 Posts
Could I get away with grounding the fuel rail connection right off the connector or is there more to it than that?

I'm thinking this could burn out the ECU without the injector in the circuit

and going a step ahead I think the injector would burn up before long with no fuel going through , and then burn out the ecu ..but it might be slightly safer for the computer if you "checked" that way
 

·
Registered
Joined
·
7 Posts
Discussion Starter #11
the question I have to ask is where on god's green earth did you find a predator carb , still worth using , and how just how big is it ?

a pic would really awesome !!

Here are a couple pics of the carb mounted up. Still waiting for some fittings to arrive so I can finish up the boost controller.
 

Attachments

·
Registered
Joined
·
7 Posts
Discussion Starter #12
Ok, so I hooked the fuel rail back up to it's connector and grounded it out and it fired right up! The engine RPMs keep slowing increasing until I shut it down. As I mentioned earlier, I don't have the boost controller fully installed so the wastegate is staying closed, would this cause the motor to keep increasing speed? I checked my vacuum lines for leaks and they seem to check out. There is no idle circuit on this carb, only a fuel mixture adjustment, that I can see.
 

·
Super Moderator
Joined
·
11,698 Posts
I'd say the idle speed increase is probably some vacuum leak bypassing the throttle plate in the carb

the old log motors well get a run away throttle if one of the hoses connecting the TB to turbo or turbo to engine gets ripped or bursts

main reason they went away with the second gen motors
 

·
Registered
Joined
·
7 Posts
Discussion Starter #14 (Edited)
I'd say the idle speed increase is probably some vacuum leak bypassing the throttle plate in the carb

the old log motors well get a run away throttle if one of the hoses connecting the TB to turbo or turbo to engine gets ripped or bursts

main reason they went away with the second gen motors

Took the carb off and it looks like the gasket under the carb going to the turbo was leaking bad. I think I've got some felpro gasket material laying around I'll make up a new gasket and give it another go.


Update: still wanting to rev to the moon upon startup :(

Update #2 : Thought maybe the brake booster was bad so I disconnected the vacuum hose and plugged it off, still no luck.

Update #3: Got it idling with the help of my gearhead brother. We adjusted the dizzy until it wouldn't run then started adding timing back and adjusted the idle screw on the carb (that I couldn't find). Ended up fouling the plugs due to adding a bit too much fuel. I'm going to hold off on anything else until the fittings come to plumb in the boost controller tomorrow.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #15
Bump

After hours of researching and information gathering I've come to the conclusion that I will need to convert the factory Hall Effect dizzy to something else so it can fire the coil off. I believe there is no other option in my situation of converting to carburetor.

Anyone here know how I can, if possible, convert from hall effect to hei possibly?
 
1 - 17 of 17 Posts
Top