Reduced engine power
Thread Starter
Racer
Joined: Apr 2014
Posts: 346
Likes: 7
From: Jacksonville N.C.
Reduced engine power
Hey guys im hoping to finally put this issue to rest but I need your help. I have a 2002 z06 that's modified H/C/I/E and im having an issue while cruising around on the highway. For example if i'm cruising in 5th or 6th gear at around 1600 RPMS and I let off the throttle even for a split second I get reduced engine power, which I can reset and then get on my way. The codes I pulled are P1220, p1221, p1515 along with c1214 and c1278. I know for a fact that some of those are related to the EBCM and im planning to pull that and re solder the relay tomorrow. However any help with the reduced engine power is greatly appreciated.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
WELL,,, In a nut shell,,, you have a THROTTLE POSITION SENSOR or something in that circuit issue.
I don't know if you are running the OEM C5 LS TB or a C6 TB BUT,,, The Throttle sensors are not doing what the PCM & TAC Module expects them to do..
If it were me,, (prior to throwing cash and parts at it) I would:
1- Check EACH connection on the TPS, Accelerator Position Sensor and the TAC Module.
2- The wiring harness that runs down the drivers side of the engine intake manifold bends around a metal bracket at the back of the manifold. Those wires have been found to be Cut and chaffed.
3- Check the actual ignition switch supplied voltages at the fuses for the TAC Module, & PCM with a meter to chassis ground. MUST BE FULL BATTERY VOLTAGE!
If all checks out, replace the Throttle Position Switch/sensor.
BC
I don't know if you are running the OEM C5 LS TB or a C6 TB BUT,,, The Throttle sensors are not doing what the PCM & TAC Module expects them to do..
If it were me,, (prior to throwing cash and parts at it) I would:
1- Check EACH connection on the TPS, Accelerator Position Sensor and the TAC Module.
2- The wiring harness that runs down the drivers side of the engine intake manifold bends around a metal bracket at the back of the manifold. Those wires have been found to be Cut and chaffed.
3- Check the actual ignition switch supplied voltages at the fuses for the TAC Module, & PCM with a meter to chassis ground. MUST BE FULL BATTERY VOLTAGE!
If all checks out, replace the Throttle Position Switch/sensor.
BC
Thread Starter
Racer
Joined: Apr 2014
Posts: 346
Likes: 7
From: Jacksonville N.C.
Thanks bill ill take a look. I did pull the connector at the throttle body (its a fast 90 same as the manifold) and take a look but nothing so I pulled the throttle body itself to clean it up a bit (oil grime), and found that not only is there still residual oil pooling in my intake (just added a catch can) but it seems the previous owner or engine builder decided not to use the supplied valley cover bolts for the fast intake and subsequently cracked the bottom shell. So now into the rabbit hole I go. Hopefully this doesn't keep me off the road for too long.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Thanks bill ill take a look. I did pull the connector at the throttle body (its a fast 90 same as the manifold) and take a look but nothing so I pulled the throttle body itself to clean it up a bit (oil grime), and found that not only is there still residual oil pooling in my intake (just added a catch can) but it seems the previous owner or engine builder decided not to use the supplied valley cover bolts for the fast intake and subsequently cracked the bottom shell. So now into the rabbit hole I go. Hopefully this doesn't keep me off the road for too long.
The vacuum leak that could be or is being causd by those cracks could VERY WELL be causing your issue.
When you add mods to a LS Engine and the air flow through the MAF is too far out of whack, it will go into reduced power mode to protect the car from WAY OUT OF WHACK air flow values!! When you come off the throttle, manifold vacuum is great and your getting air through those cracks.
Install the proper bolts and try to repair bottom of the FAST manifold. You have to spend a LOT of time degreasing the bottom pan before you can propery repair it. I would use a proper plactic epoxy. Look for a product by PC-7 or JB weld Its a two part plastic epoxy. It works fantastic!
Here,,, this test should help! LOL!!
Just clean, degrease, sand and reclean and use a GOOD quality two part epoxy.
Bill
Last edited by Bill Curlee; Jun 9, 2015 at 07:57 PM.
Thread Starter
Racer
Joined: Apr 2014
Posts: 346
Likes: 7
From: Jacksonville N.C.
Thanks again Bill, just for my knowledge do you think that during deceleration with the car in gear the cracks are allowing air through causing the reduced power mode? Because outside of that the car runs and idles just fine.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
I would say YES! You know its damaged and cracked. Until you fix and solve that problem,, you are never going to be sure it isnt th issue..
The manifold vaccum on decell is very high. If its going to leak,, its going to leak then!
Bill
The manifold vaccum on decell is very high. If its going to leak,, its going to leak then!
Bill
Thread Starter
Racer
Joined: Apr 2014
Posts: 346
Likes: 7
From: Jacksonville N.C.
alright then off to the store for some brake cleaner and epoxy. Ill report back in a couple days after I get it repaired. Should I be concerned about replacing the intake manifold seals as well?
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
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Thread Starter
Racer
Joined: Apr 2014
Posts: 346
Likes: 7
From: Jacksonville N.C.
I pulled the fast 90 manifold apart and cleaned and degreased everything twice. I haven't repaired the cracks yet but luckily they don't go all the way through. I'll repair it tomorrow but I'm still waiting on gaskets to come in. Unfortunately I don't think this is going to help the reduced engine power problem. Regardless getting the oil grime out of the intake makes me feel better lol. I will report back after getting everything back together.
Last edited by Impulsive goat; Jun 13, 2015 at 08:30 PM.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
To "HELP" limit the intake of oil into the intake manifold from the PCV..system, you will need a good properly engineered Catch can.
You will still get some oil into the intake manifold but it will NOT be any where near as bad as it is now.
Bill
You will still get some oil into the intake manifold but it will NOT be any where near as bad as it is now.
Bill
Last edited by Bill Curlee; Jun 14, 2015 at 11:51 AM.
Thread Starter
Racer
Joined: Apr 2014
Posts: 346
Likes: 7
From: Jacksonville N.C.
I hear ya, I installed one just before me and a buddy went to the tail of the dragon even seafoamed the top end real good. Im just really surprised how much was built up in there. Damn thing should have came with one from the factory. By the way I run a ADD W1 version 1 catch can on the vette and a UPR can on my bad weather GTO beater, both are baffled cans. Both seemed well liked on the forum as well.
Thread Starter
Racer
Joined: Apr 2014
Posts: 346
Likes: 7
From: Jacksonville N.C.
Well Bill I repaired the intake and put it all back together with fresh seals but managed to drop the last throttle body bolt down the battery compartment abyss last night.
I took a break and got back at it this morning, pulled the wheel and wheel well liner to find the sucker but noticed there's a very small vacuum line down aft of the tac/pcm that's not hooked up and the bracket for the pcm is broken on one side. ill be pulling those out later on to replace the bracket and figure out where that line goes. Still haven't found the bolt and still have not fired up the car yet.
I took a break and got back at it this morning, pulled the wheel and wheel well liner to find the sucker but noticed there's a very small vacuum line down aft of the tac/pcm that's not hooked up and the bracket for the pcm is broken on one side. ill be pulling those out later on to replace the bracket and figure out where that line goes. Still haven't found the bolt and still have not fired up the car yet.
Thread Starter
Racer
Joined: Apr 2014
Posts: 346
Likes: 7
From: Jacksonville N.C.
Got it all put back together this morning and took it out for a drive and no issues so far. I feel like it runs a bit stronger, could be due to the fact that I cleaned all the residual oil out of the intake and used fresh seals on everything. The idle is rock steady at 900 so it looks like I got everything installed right, the abs/traction control codes are gone and I haven't seen reduced engine power yet but I haven't really tried to induce it. Will report back if anything else pops up. Thanks for the help Bill.
Team Owner
Joined: May 2001
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From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
ANY issues with the TAC module, be they connector contamination or corrosion related or otherwise, will set a DTC and the PCM will set REP.
Thread Starter
Racer
Joined: Apr 2014
Posts: 346
Likes: 7
From: Jacksonville N.C.
I did pull the TAC and PCM when I was searching for my missing throttle body bolt. The connectors looked fine I cleaned them anyway and put the back together with some dielectric. There was no corrosion of any kind in that area or any evidence that there was ever any battery leaking issue, so I think i'm clear on that front. I got to know those wire bundles very well during my search and they all look good no chaffing or rubbing either. I was actually kind of surprised. Obviously the pcm bracket didn't break itself so I'm a little curious about that, however that vacuum canister didn't cap itself off either(both the line and tee fitting were capped? very odd). Really weird I know but its fixed now. Ill see if I cant break it this weekend.
Team Owner
Joined: May 2001
Posts: 36,836
Likes: 243
From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
I did pull the TAC and PCM when I was searching for my missing throttle body bolt. The connectors looked fine I cleaned them anyway and put the back together with some dielectric. There was no corrosion of any kind in that area or any evidence that there was ever any battery leaking issue, so I think i'm clear on that front. I got to know those wire bundles very well during my search and they all look good no chaffing or rubbing either. I was actually kind of surprised. Obviously the pcm bracket didn't break itself so I'm a little curious about that, however that vacuum canister didn't cap itself off either(both the line and tee fitting were capped? very odd). Really weird I know but its fixed now. Ill see if I cant break it this weekend.
Thread Starter
Racer
Joined: Apr 2014
Posts: 346
Likes: 7
From: Jacksonville N.C.
Well guys I've been driving the hell out of it and I cant seem to get it to break so it looks like you've solved my issues. Thanks again for all the help, gotta love the tech support this place provides. Drive safe out there.