Intake Backfire after GT40P HCI Swap

[LightningNThndr]

Hey guys! I recently did a Head/Cam/Intake Swap and now Im having serious problems with my car. I had a mostly stock 306 (with cold air intake, flowmasters, offroad H and Shorty headers) and it ran reliably before I began the swap. I installed a set of GT40P heads, Trick Flow HP springs, TFS Stage 1 cam, and Cobra upper and lower intake. I left the stock throttle body and EGR spacer. While I was working on the engine, I replaced the air temp sensor, and the coolant temp sensor. I installed new plugs and PCV valve. When I went to fire it up, it drove fine, but a little rough. I adjusted the timing to 12 degrees and it seemed to run great. I drove the car to Autozone which is about a half mile away and bought a replacement battery wire, but about halfway back home, it started popping through the intake. I pulled over and let the car cool off, but it still does it. It sounds like a popcorn maker under my hood. I bought a code scanner and came up with 4 codes. the first is bad air temp sensor (which is new), the second is bad coolant temp sensor (which is new), the third is bad EGR sensor and the fourth is bad MAF. While I was working on the car, I did a smog pump delete, but I dont imagine that it would cause these problems, since the thing was just hanging under my car with loose hoses anyway. I have tried changing my timing anywhere from 0 btc to 20 btc and nothing seems to help. Any thoughts would be much appreciated!

 

[the pony boy]

with all those sensors coming up bad o would think its a electcal problem.maybe one of the connectors is loose or you have a bad ground. good luck phil

 

[SVO1]

X2 on ground/loose connector

 

[LightningNThndr]

Well, I tried everything I could think of, I checked all of the sensors, connections, and every possible setting for timing and nothing seemed to work. I finally got fed up and decided to tear the engine back down. When I drained the oil from my engine, it had a lot of coolant in it. Next, I pulled the upper manifold and found a hell of a lot of fuel in the 8th port. Then, when I pulled the valve covers, I discovered to my horror that the pushrods had punched through the rockers!!!! I have never seen anything like that before, but I suspect it is caused by bad PTV clearance. I will pull the heads tomorrow and see if it looks like the valves and pistons touched at all. Ill keep you guys updated!

 

[Mustang5L5]

I've seen many guys run the TFS1 with 40P's and the TFS springs with no issues. I'd be surprised if you had PTV clearance issues. Did you clay first before putting the heads on? Most times i've seen PTV hits, the pushrods had bent.

Only thing i can think of if it's not PTV issues is that the rockers were fatigued from use, and the combination of a cam with slightly higher lift, and the addition of stronger springs did them in. Are those the explorer rockers? or your original Mustang rockers (which are the same thing)

 

[LightningNThndr]

They were the explorer stock rockers with the mustang stock pushrods. After pulling the lower intake manifold, It appears that possibly the pushrods somehow landed on top of the lifters, so they werent able to compress down into the lifter. I dont know if this is a product of bad valve lash or if it happened because the pushrods got bent due to valves impacting the pistons. I didnt clay the pistons because I have seen many people run this combination without any problem, but I guess every case is different. I have .030 over pistons with 4 valve reliefs cut into them, but its quite possible that they are slightly taller than the stock ones.. Hopefully Ill know more when I get these heads off. Now to figure out how to remove those pain in the ass Mac headers again.....

 

[LightningNThndr]

Well, the damage appears to only be on the exhaust side. The pushrods were bent out of shape, but there is no damage to the valves or pistons! I was unable to squish down the center of any of the lifters though. Anybody know what would cause this?

 

[Mustang5L5]

Hmm, it's possible the pushrods "jumped" on top of the lifters after the rockers broke...unless those two have intact rockers. That is a very odd break. You are right...it's a popular combo and i've never seen anything like that at all. Something was obviously out of whack..but i can't see anything wrong from the pics

 

[LightningNThndr]

I think you are correct.. The pushrods that were on top of the lifters were the ones that had damaged their rockers. I still dont know why the lifters feel solid though...

 

[LightningNThndr]

I called trick flow last week and they thought it might be due to the fact that their cam has a slightly smaller base circle, so I should be running a longer pushrod. I picked up some hardened pushrods that were .1 longer, installed a new timing chain and also put in some cobra 1.7 roller rockers. Put the engine back together and it is still backfiring through the intake, but this time much louder. It sounds like a gunshot going off under the hood! I have no clue why it would be doing this! Perhaps I didnt set the valve lash correctly? I turned the bolts a half turn past zero lash. Some of them still felt a touch loose and some of them only turned about a quarter turn before they stopped. Could my lifters be out of whack? Thats about the only thing I havent replaced on this car!

 

[LightningNThndr]

Could it be my springs? I bought springs from a guy on craigslist that said they were the springs that trickflow supplied with their heads. I wonder if it was a bad idea to use them. It seems to fit well, but I dont really know..