Update on the Cobra

[94cobra69ss396]

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]

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]

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]

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]

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

[Damian]

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]

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]

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

[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.

[Vettezuki]

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

[94cobra69ss396]

Yes, the 347 feels a lot more powerful. What I mean is the smoothness of the engine. The 347 just didn't feel right.

[Vettezuki]

Doh! Yeah that makes sense.

[94cobra69ss396]

So it's not fixed, f___! I had to run over to Phil's house last night so I jumped in the Cobra and started it up. I let it idle for a minute before I started to leave. When I let the clutch out the car started to die and when I tapped the throttle I got a lean miss and the car died. It fired right back up but if I gave the throttle a quick tap it would lean miss. If I went slow on the throttle it would rev up fine though. I let it warm up a little more and then started down my street holding the revs at about 2000 in 2nd gear at 25mph and the car stumbled the whole time. When I got out to the main street I kept the revs below 2000 and it was fine. By the time I got to the freeway the car was warmed up so on the freeway in 6th gear the rpms are around 2200 at 70. The car ran fine on the freeway. However, if I dropped it into 4th and brought the rpms up it would stumble. I think I might have an injector or two that isn't flowing well under partial throttle.

[Vettezuki]

Is that a MAF or speed density setup? If it's MAF, have you checked/cleaned it? I've had stumbles in both my Mazdas at over 100k miles and in both cases it was literally just a matter of cleaning the MAF.

[fiveohwblow]

You replaced the plugs right? I see you mentioned it earlier and had to wait for a paycheck but no mention of whether or not it was done...

[94cobra69ss396]

It's MAF and I thought I had cleaned the internals when I switched the housing from the 80mm to the 90mm but now I don't remember. So I picked up a bottle of MAF cleaner and will try cleaning it to see if it makes a difference.

I did replace the plugs and that was an improvement as well.

[Damian]

I'm glad I read your post about the carbon canister full of fuel. I checked that on mine thinking that was my problem and mine is leaking out the seals on the top. I need to find another one and they aren't cheap!

Did cleaning the MAF help then?

[94cobra69ss396]

I haven't had time to clean it yet. Hopefully I will Saturday. If you think the EVAP canister is a problem, you can bypass it to test. Just plug the vacuum line going to the purge valve.

[Damian]

Im just gonna get some of that plastic glue and put it around all of the seams.

[94cobra69ss396]

The replacement one for my Cobra is only $45 so I'm just going to buy a new one.

I pulled the MAF this morning and it didn't look dirty but I sprayed it down with MAF cleaner anyways just to see. Then I took it for a test drive and it didn't make a difference.

[Shaolin Crane]

Sure sounds like timing to me, did you check your coil pack?

[94cobra69ss396]

I have two coils (MSD and stock) as well as two ICMs and it does the same thing with all. I also tried another distributor with the same result.

[enkeivette]

Funny, I was thinking lean condition for the stumble. I wouldn't have thought vacuum leak though, nice work!

[94cobra69ss396]

It's not fixed yet, it still has a slight stumble at light throttle. I ordered a screen/filter kit for the injectors today and plan on cleaning the injectors once I receive the kit.

[enkeivette]

Big cam V8s just suck fuel with rapid throttle change. I put on the biggest squirter nozzles and cams I could, still jumps up to 16:1 with low rpm quick throttle change. Hook up a wide band and watch it.

[94cobra69ss396]

I don't have a big cam, it's actually smaller than the old Crane cam that was in the 302. The old cam had 220/220 at .050, .530 lift and a 110 LSA. The new Comp cam has 208/216 at .050, a .544 lift and a 114 LSA. Also, I can only feel it at a light load at high rpms like on a flat road. If the road starts going up hill and I have to give it more throttle, I don't feel it.

[Shaolin Crane]

Did you check the lower intake gasket?

[94cobra69ss396]

I replaced them once already when I replaced the head gaskets. So unless I screwed up installing them that shouldn't be the issue.

[enkeivette]

I replaced them once already when I replaced the head gaskets. So unless I screwed up installing them that shouldn't be the issue.

Mine blow out every so often even though I install them with silicone adhesive. They blow out even quicker without the adhesive. Boost plus v configuration engine equals intake manifold gasket issues.

[94cobra69ss396]

I'm only making 10psi which is the same as I was before with the 302. I'm also running the same heads and intake as before and I never had an issue with it blowing intake gaskets. I highly doubt that's the issue but I'll take a look at them when I pull the upper intake off.

[94cobra69ss396]

I cleaned the injectors and installed new screens and seals. It helped but it still has the light stumble. I also took a look at the lower intake gaskets but they looked fine. I even pressurized the crankcase to see if they would leak but they didn't.

[enkeivette]

I'm only making 10psi which is the same as I was before with the 302. I'm also running the same heads and intake as before and I never had an issue with it blowing intake gaskets. I highly doubt that's the issue but I'll take a look at them when I pull the upper intake off.

PSI, I know your perception is skewed, but 10 psi is a lot on a street V8. Its not an Evo :)

[BADDASSC6]

PSI, I know your perception is skewed, but 10 psi is a lot on a street V8. Its not an Evo :)

not really.

[94cobra69ss396]

Doesn't really matter as the intake gaskets aren't leaking and I've never had an issue blowing them. When I was cleaning them number 8 injector was the only one that didn't have a nice stream at first. I thought it was going to have an issue only because when I changed the spark plugs a while ago cylinder 8 plug just looked a little lean compared to the others.

[Vettezuki]

Doesn't really matter as the intake gaskets aren't leaking and I've never had an issue blowing them. When I was cleaning them number 8 injector was the only one that didn't have a nice stream at first. I thought it was going to have an issue only because when I changed the spark plugs a while ago cylinder 8 plug just looked a little lean compared to the others.

I know on LS motors builders will sometimes specifically compensate flow rate for cylinder 8. I think mine is 35#, while the others are 32#, something like that.

[BADDASSC6]

One of the PSCA guys that works on base has a turbo SIlverado. I was talking to him about tuning and he stated that when he tunes he uses high temp tape to hold thermocouples on each exhaust primary. The EGT of each cylinder is an indicator on how lean / rich it's running. He then add impedance inline with the fuel injector to balance out the flow.

Formula ford guys use a surface pyrometer and insert baffles into the plenum to balance out EGTs since with the carb motors fuel doesn't flow evenly to all four cylinders.

Get a A/I inventor and catalog that shit. I have one from Traqmate if you want to borrow it.

[94cobra69ss396]

I finally have this issue resolved. There were two causes. The first was the wiring harness to the O2 sensors had three wires that the insulation was cracked and bare wires were touching each other and the oil pan. I called Ford to see if they still carried it but they didn't. So I tried Pick-A-Part and lucked out. Usually they only have V6 SN95 cars but this time they had two '94 5.0's so I pulled the better looking harness. The other issue was that the idle stop screw and IAC bleed screw needed to be adjusted. The car now idles at around 950rpms and no longer has the light throttle surge.

http://motorgen.com/pic/data/500/20140215_180101.jpg

[blackax]

Congrats of finding the issue.

[Vettezuki]

Awesome! Electrical related problems are some of the worst.

[94cobra69ss396]

Thanks. Back when Steve tuned the car he mentioned that one of the O2 sensors was acting slow. This explains that too.

[Vettezuki]

My MIL light that never went off on the Devil Aveo was because of a frayed O2 wire. Taped it up. Problem solved.

[Leedom]

Glad you figured it out Ron.