Update on the Cobra - Motorgen - Automotive Events, Meets, Cruises and Forums

94cobra69ss396 · 11-09-2013, 09:54 AM

It's been a little slow in here so I decided to add some updates on some of the things I've been working on. The Cobra had been running pretty good after I got the final tune done. That was up until one day that I was heading out of town to visit a customer up north.

I decided to drive through a car wash on my way out. The place I go is a drive though wash and I was just exiting it when the car all of a sudden died and wouldn't start. As I was trying to figure out why I discovered that the MSD box had died. So I bypassed the box and ran the car off the coil. The car ran great the whole trip with the exception that It wouldn't rev past 4500 rpms or the boost would blow the spark out.

When I got home I ordered a new Mallory box to replace the MSD box. I ordered it from Summit and when it arrived I installed it. The car ran great after installing it. About a week later I had to go to another customers up north. The car ran great all the way up there and for the couple days I was there. I'd driven roughly 500 miles. On the way home I got stuck in traffic around San Jose. That was the first time The car had sat for more than a few minutes without going 40 mph or faster. Anyways after about 30 minutes the car died. Luckily I was on a side street so I pushed the car into a parking lot to look at it. Since that was the same issue I had with the old box I tried bypassing the box again and the car fired right up and I drove the rest of the 500 or so miles home without any issues.

I called Summit and got a replacement box which now works fine. However, I now ran into a new issue where at a light cruise after the car warms up I get a misfire. I tested the coil and the grounds thinking it may have something to do with them but they tested fine. I was so frustrated with it that I called Phil and asked if he would take a second look at it to see if maybe I missed something.

As we were looking at it he mentioned being able to smell raw fuel which I also noticed a while ago but hadn't looked into. Phil said that the misfire could be caused by the EVAP canister being full of fuel. So the following day I pulled the EVAP canister off (it's located in the front passenger fender) and sure enough, it was full of fuel. I poured the fuel into a gas can and the misfire is gone. I still need to buy a new EVAP canister as well as a new set of plugs but have to wait until I get paid again.

Vettezuki · 11-09-2013, 08:08 PM

I've never heard of an EVAP canister filling with fuel! Did this take a looong time, or is something else causing it to fill rapidly.

94cobra69ss396 · 11-09-2013, 08:54 PM

I think it has happened over a long period of time and finally reached the point that when the purge valve open at a cruise that it was siphoning fuel into the intake. It would take about 15-20 minutes of cruising before it would happen. I've been smelling fuel for a few months but only when I ran the A/C. However, in the last couple weeks I have been able to smell it when I opened the hood.

Vettezuki · 11-09-2013, 09:51 PM

I guess my point was you don't suspect anything else is causing it to pick up more fuel than it should? I've just never heard of this, though obviously your brother has.

94cobra69ss396 · 11-10-2013, 08:28 AM

I know the EVAP was the cause because it was full of fuel and now that I drained it the misfire is gone.

Damian · 11-10-2013, 09:26 PM

When my MSD box crapped out, it took out my coil too. Glad you figured it out though. On a side note, I should check mine as well. Mine has a miss at idle as well.

94cobra69ss396 · 12-15-2013, 08:33 AM

Time for an update. So even though the EVAP was full of fuel, it was not the cause of the stumble I was feeling at a cruise. I thought that it might have been caused by the magnetic pickup in the distributor since I'd already tested the coil and ignition module and it wasn't either. I called up GTR and asked if they had a distributor I could borrow. They said that the only one they had was on their race car but that I was more than welcome to borrow it. So I ran over to their shop and pulled it off the car. I installed it on the Cobra the following day and took it for a test drive. That wasn't the issue.

I swapped my distributor back in and took theirs back to them. While there I was talking to Ricardo about the issue and said my next thought was something Steve had mentioned to me when he did the tune which was that the location of the bypass valve. With the UPR intake tube the location moved from directly in front of the blower inlet to the front of the tube which is about 4 inches behind the MAF. This position can cause air to re-enter the MAF from the backside causing the stumble. Ricardo said an easy way to test it is to just remove the supercharger belt so I tried it. But it still had a light stumble. It wasn't nearly as bad but I could still feel it.

Since it did improve it I decided that I was going to move the bypass location. I borrow a plastic welder from a friend and started practicing on another intake tube I have. However, I just couldn't get it to hold like I wanted. My next thought was that instead of moving it that I could use some aluminum tubing inside the intake tube to direct the air towards the blower. So I pulled the bypass valve off to see what the diameter of the hole was. While I had it off I tested the bypass valve and found that it was bad. When I tried to create vacuum with my vacuum pump it just leaked. The diaphragm must be cracked which was causing it not to open and would creat a vacuum leak. That explains why I still had a stumble without the blower belt on.

I called GTR to see if they had a replacement in stock but they didn't. I then went online to see if any parts store carried the Bosch bypass valve I had and found that a factory Audi/VW/Saab valve was an upgrade to the one that I had. I went to Ontario VW and picked one up. Sure enough, that was the issue!

joedls · 12-15-2013, 08:59 AM

Great news. I know it's a relief to finally figure it out.

94cobra69ss396 · 12-15-2013, 10:30 AM

It is. I think it's been bad since I built this 347 because it never has seemed to run right. Not that it ran bad, it just hasn't felt like it did with the 302. Now it does.

Vettezuki · 12-16-2013, 03:13 AM

Quote:

Originally Posted by 94cobra69ss396

It is. I think it's been bad since I built this 347 because it never has seemed to run right. Not that it ran bad, it just hasn't felt like it did with the 302. Now it does.

Awesome when you find out a nagging issue isn't a major expense.

PS should it feel a lot gnarlier with the 347 vs. 302.