hot start issue: please help
 

Hello All,

I'm having a hot start issue with my FC w/ LT8. It was fine before but started acting up recently and I'm not sure what it is. I replaced my injectors and clips thinking they may be leaking (They were Venoms), but the problem still persisted. A couple of threads I saw lead me to believe that I need to check the CAS, but I'm not exactly sure how to do this.

Symptoms and behavior:

On a cold start, the car starts perfectly without any issues.

On a hot start about 20-30mins after shutting it off, the car will crank for what seems like 7-10 seconds and finally fires up, misfiring horribly. If I give it gas, it will remedy the misfiring faster, but it's still there.

My idle is a little lobe-y; it bounces between 900-1100. I'm running 750cc primaries.

Proposed solutions:

Check and make sure my CAS is working properly. As referenced here: https://www.rx7club.com/showthread.p...ight=steve+kan . Steve told this gentleman to replace his CAS and it solved all of his problems. How do I check if mine is bad? I've searched on inspecting the CAS and can get a replacement, but I want to make sure the replacement I get is in good shape or know whether or not to even replace mine. I've been told recently that the timing is fine.

Replace fuel filter. I don't really think this is the problem but I'm going to do it anyway for good measure.

Any help or input you guys can give will be greatly appreciated.

Thanks,
Jaime

If your CAS is bad. You will get RPM and or REF and or HOM errors.

If its not pumping out errors i highly doubt its cas.

If your car was running fine and then went bad, have you done a comp test?
Thats were you start. Then look elsewere

Thanks! I get errors every once in a while but usually a turn off and on will get rid of them. The motor was recently rebuilt (8k miles) and did 300whp, so I don't think it's the compression, but I'll check that.

Bad injectors can do what your car is doing

I highly doubt it's the injectors as they're brand new Fuel Injector Clinic injectors that haven't even had 1k miles of use yet. Same behavior prior to swapping them out, pretty much identical. I just got the fuel filter so I'll install that tomorrow and let you know how it goes. Thanks again!

It just hit me.
Id say your car is suffering from fuel boil.

Have you got a AFR meter?
Whats your idle AFR?
IF its too lean it can cause your problems.

It bounces between 11.5-12.1 when it lobes at its worst. Usually high 11's. No amount of tweaking on the idle or 1000 maps changed it when I tried.

Can you do a datalog when its happening.
And another datalog when the car is running normally.

I think i can help you for sure with the above.

Sorry for taking so long, and hopefully you can still help me out. I didn't get a chance to drive around, but I figured it'd be useless considering this issue is only at starting.


Well, here's my cranking and idling datalog. Sometimes it will do the same behavior even on the first start of the day. It misfires like crazy until the AFRs slowly start to drop to around 10-11. Upon first fire, I have to crank for a little bit longer to get it going on its own and if I leave it idling without giving it some gas, it will die until the AFRs get to around 10-11 then it will idle nicely but a little bouncy. If I rev it from 2-2.5k after initial fire, it will get to better idle quality faster, since this causes the AFRs drop quicker. It seems that I'm running lean at initial crank and for whatever reason giving it more gas will slowly but surely drop the AFRs until it idles nicely.

I can take a video of it soon, when my camera comes in so you can see the RPMs, AFRs and hear the misfire.

Please help! Let me know if there's an easy way for me to get my maps off the microtech and uploaded here.

Thanks.

Also, here are some screencaps if that helps any:

http://i17.photobucket.com/albums/b6...screencap1.jpg
http://i17.photobucket.com/albums/b6...screencap2.jpg
http://i17.photobucket.com/albums/b6...screencap3.jpg
http://i17.photobucket.com/albums/b6...screencap4.jpg
http://i17.photobucket.com/albums/b6...screencap5.jpg
http://i17.photobucket.com/albums/b6...screencap6.jpg
http://i17.photobucket.com/albums/b6...screencap7.jpg

In the idle and 1000rpm screens


Make the 05HG 2.76
And the 00HG 3.86

In both of them.

See if that helps.

Looks to lean on crank.

Also make the 10HG in both idle and 1000rpm screen 2.15

I've done the above and I think it helped a little, but I'm still firing only one rotor (sounds like) on initial start until I blip the throttle to about 2.5k and I start hearing the other rotor firing. If it helps at all it seems that revving the motor to 2.5k and letting it drop and revving it again help more than leaving the motor at 2.5k. Any other ideas?

Thanks again for the help

Just wanted to update the thread:

Seems like the problem this whole time was my FPR. The diaphragm was leaking, causing unmetered fuel to be dumped into my intake manifold. This was the explanation for the lumpy idle and hot starting issue. It was basically dumping fuel into the intake when I turned the car off and I'd have to let it sit for a LONG time to get it unflooded, hence why I thought it was a "hot start" issue.

Thanks to everyone that tried to help.

Jaime

was your FPR expensive or difficult to replace?

Replaced it with stock.

mine acts the exact same way so im currently looking here to see of someone has an FPR for sale

Sorry, not hard to replace or expensive.