Stumbling and breaking up problem ??

josh young

Member
Joined
May 12, 2008
The car has started acting up some lately. It runs fine under normal driving, idling, and moderate acceleration. The problem comes up when you go WOT, it does not do it all the time either. It seems like it surfaces when the boost is in the 15 or so range, I have it set at 18. It also seems like the hotter the weather, the worse it is. The problem has NOT developed since I installed the following parts, it done it with the old ones. Here is a rundown on what I know is done to the car:

The following parts have been put on sinse the issue has started:
I have recently replaced the plugs with NGK UR5's gapped at .35.
I have replaced the coil packs with ones from Kirban's.
I replaced the module with a new Duralast, the old original one was mushy and needed replacing.
I replaced the vacuum lines, and zip tied them.
I used grease on the coil pack, module, and wires.

The following parts were on the car before issue developed:
The car has new 60# injectors, TT chips, nearly new Walbro, filter, hotwire kit. etc.
When the car does it there is no code, no knock, the 02's are good in the 770-820 range, BL's are in the 120's all the time. It has had valve springs also. I took it out one night last week, the air was cooler and it ran without any issue. At 18psi the fuel pressure is rising like it's suppose to to 60-61 psi. I'm currently running the turbo tweak 110 chip with higher timing and the 18psi, waiting on cool weather to turn it up a little more. I'm running 110 leaded also with a heated o2 kit. It has stock style MAF, but it goes to full reading and seems good. It lays over when the issue arises, like it has ran out of steam.
Basically I'm wondering if a crank sensor or a cam sensor could cause this issue. Whatever is going on is related to the outside temps, cooler weather it runs like a top. When the weather gets hotter it has this intermittent issue. The temps are also good in the 170 range on an 85 or hotter day. Any input or thoughts are greatly welcome. Thanks for reading this long write up guys. If I've left out anything just ask.
 
I had the same problem, changed out a large list of parts. My cam had 2 wiped lobes, which caused the stumble under boost. Once I replaced the cam, no more issues.
 
I had a vac hose that kept coming off .. ran fine 1/8 then started breaking up bad
 
Start the car. Unplug the cam sensor. Motor should continue to run. Take it for a ride a see if it still breaks up.

Rick
 
I guess it needs to be running when you unplug it? I guess it wouldn't start at all if you unplugged it first, just seems kind of tight to get my hand in there with everything rotating. I have a Casper's tool with the car. Would setting it with that help any or is the sensor most likely shot?
 
Yes it has to be running.

It's not a problem to go wot with the cam sensor unplugged but you are just looking to see if the problem is still there not run 1/4 mile. A quick hit should do it.

Never have I had any luck with ignition parts other than ac delco. The off brands all have some side effect.

Rick
 
Do you remember the psi listed/written on the sticker of the chip?
 
I replaced the cam sensor cap with one from Tomco. After doing some digging on the site it seemed liked several other members had issues like mine and the cap was the cause. I took it out tonight and made 5 pulls and it ran the same each time, no stumbling or letting down. I just wanted to update my thread, so others with similar issues can see the end result. Thanks guys for all the opinions and inputs, they were greatly appreciated!
 
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