3.6 Backfire on start-up

[Jcon]

Still sorting some minor problems on the 3.6 conversion. It's a 92 3.6, light weight fly wheel, Cyntex chip, Custom Exhaust.

When my car sits for a couple of days it's tough to start. It needs to crank and when it catches it's rough and wants to or does backfire.

This all clears in about 30 seconds.

It also has a slight hunt in the idle. You can hear it and slightly see it on the tach. I'm talking a 100 RPM swing.


Any thoughts

Jeff

[Mike Feinstein]

Jeff,

I understand that there's some sort of vacuum pump that serves to ease starting and also has some emission control functions. It's often removed on conversions...I'm not sure why. My car, and many others that I'm aware of also require some cranking when cold. Once it starts and stumbles for a few seconds, it runs fine. Installation of this pump requires an engine drop. Perhaps others who know more can chime in.

Also, did Cyntex burn your chip for your box? Reason I ask is that I have a Euro box, but received it with a Cyntex chip burned for a US box. It's being corrected now. If you can get a diagnostic pig-tale hooked up...check and clear codes.

[Mike Feinstein]

Jeff...just copy/pasted this from a post by Craig911. Maybe he or Bill Verburg will chime in, but I believe this is related to the cold-starting situation (I wouldn't go so far as to call it a "problem"):

"When doing a US 3.6 transplant - remove & plug ALL of the Secondary Air Injection crap."

[blue82coupe]

Jcon . My 82 sc with a 95 993 engine does the same thing.I've learned to live with it. Its probably a loss of residual fuel pressure .Possibly a bad check valve . It could be the cis fuel pump causing the problem, since it operates at a higher pressure.Even though I'm living with it,it is a problem that I would like to fix in the future. Dan

[hbrand]

I found that problem to be a fuel accumulator.
Test: disconnect both wires from electric fuelpump, connect a 12 volt battery to it, let pump run 20 seconds, then start engine and observe.

thanks, harold

[Jcon]

Harold

For the far less mechanical. If the engine starts just fine after 20 seconds or so, it's a bad fuel accumulator? What this thing do exactly?

Thanks

Jeff

[blue82coupe]

It holds fuel pressure for the next start. They usually are removed during the 3.6 engine .swap Dan

[Moses]

Mine starts instantly, idles steady as a rock. It wasn't always that way. First I had a cooked DME, then exhaust leaks. Keep after it. These motors are smooth when all the issues are sorted out.

[blue82coupe]

Moses, are you running the cis fuel pump or did you swap to the 964/ 993 pump?

[Jcon]

Wish it was a little warmer to go pop the decklid..

Jeff

[blue82coupe]

Jcon. We got 10" of ice and snow Wednesday night and Thursday morning, followed by sub-zero temperatures Friday night. It brought my area to its knees.
I finished my 3.6 swap in May this year. It was the most fun that I've had with my clothes on. The biggest pains were the exhaust and cooling system. The latter I'm still sorting out.LOL Dan

[Jcon]

Wow...not that bad here. I've really enjoyed the conversion. Although thruth be told I did most of the wrenching with my wallet. 4 kids under 10 doesn't leave a lot of time for thye garage. I do want to get all the minor annoyances worked out though so hopefully while I'm on vacation this week I can get something done.

Like you I'm still working on the oil cooling. In fact my mechanic is taking the car Monday to make an oil cooler bracket for the drivers side wheel well. I took a shot at it, but my welding skills are crap. I'll do all the plumbing though.

If I figure out the problem with cold start I'll post it here.

Good Luck

Jeff C

[blue82coupe]

Jcon. I plan to post pics. of my" final solution" of my cooling system.... I think this will do it . I'll be looking for posts about our cold start glitch.Dan

[Moses]

Originally posted by blue82coupe
Moses, are you running the cis fuel pump or did you swap to the 964/ 993 pump?

Old SC fuel pump. No issues.