waxenate

iTrader: (5)

I have searched and searched and can only find one thing that might apply. I am changing fuel pump tonight but wanted to put this out there. I have a stock ls1 with LT headers as the only bolt on. Basic tune. I just started feeling a roughness between 1800 and 3000 rpm. Idle is smooth and wot is fine. I have replaced the pcv and I am getting 21in hg vacuum at idle. Anyone have an idea what it may be? Btw plugs are new and there are no codes being thrown. O2's appear to be functioning properly.

Thanks for any ideas.

RPM WS6

iTrader: (3)

The fuel pump does not sound like the answer to this problem at all. A bad fuel pump wouldn't allow for proper cold and warm starts (I'm assuming it starts well, since you didn't mention otherwise) and proper WOT operation, but then only have issues between 1800-3000rpm. It certainly wouldn't hurt to check fuel pressure at idle and under load, but I don't think this is going to be of any help with your current condition and I wouldn't replace the pump unless you've verified a low fuel pressure condition.

Based on the rpm range of your issues, my guess would be a dirty/bad MAF, or an O2 sensor issue. Sometimes front O2s will begin to degrade and present problems before setting a DTC, and having LT headers (which move these sensors further back) can exaggerate this issue.

But I would start by cleaning the MAF with some Q-tips and rubbing alcohol.

wssix99

iTrader: (5)

^ +1 This is the range where the MAF monster lives...

Is a K&N oil filter installed on the car?

waxenate

iTrader: (5)

I have a Moroso filter on a cai. Forgot to mention this is an lax in a 95 z28. I cleaned the maf with cleaner also. As far as starts it has to be keyed 3-4 times to prime the fuel line (was told its a bad check valve) The o2 sensors are the vette ones which are supposed to help offset some of the associated problems. I have monitored them through the torque app and they seem to be working. What would you suggest to verify? Disconnect them and see if the roughness disappears?

Thanks for the replies

waxenate

iTrader: (5)

Anyone else?

RPM WS6

iTrader: (3)

Based on this new information, it sounds like you might need a new pump anyway. But it still seems doubtful to me that the pump would maintain proper pressure (and thus driveability & power) below 1800rpm and above 3000rpm, but just not inbetween. Either way, it wouldn't hurt to check fuel pressure above and below 3000rpm to see if there is any discrepancy during the problematic rpm window.

I am not familiar with the Moroso filters. Are they oil impregnated cotton filters, like a K&N? If so, a simple MAF spray cleaner doesn't always get off all the oil residue that can build up on the wires over time. This is why I like the Q-tip method.

What sort of O2 values do you see when the condition is happening? Lean, rich, normal?

How do the LT and ST fuel trims look during the problematic rpm window, and how do they compare to readings outside of the window? Have you logged for cylinder specific misfires as well?

waxenate

iTrader: (5)

Not sure about the values. They just fluctuate like normal. I'm pretty much a newb lol The Moroso is like the kn. going to swap the maf with one I have on the shelf to see if that works. Also I saw in a different thread that someone ran into this type of problem when they installed a manual switch for a nos system. I installed a switch for a set of halos not long ago. Not sure how that could affect anything as I tied into a wire that controlled the lights for the power source. Also do you think disconnecting the o2s would let me identify if that is an issue?

Thanks

waxenate

iTrader: (5)

Ok...fuel pump changed and starts on first key turn....swapped maf and still have the roughness. I guess next is spark plugs/wires

waxenate

iTrader: (5)

Ok...fuel pump changed and starts on first key turn....swapped maf and still have the roughness. I guess next is spark plugs/wires

RPM WS6

iTrader: (3)

Well, at least it starts better with the new pump now.

With the MAF ruled out, if such basics as the plugs/wires don't take care of the issue, then O2 sensors might be my next guess. But it would be helpful if you could scan the O2 values and the fuel trim values during the window in which the condition is occuring. Misfire data would also be useful.

waxenate

iTrader: (5)

As it usually goes now I'm having problems with my phone in using with the torque app lol! I have no misfires being recorded. I'm really doubting its plugs as they only have about 6k on them. But you never know. And yes the start issue being resolved is very nice Thanks for all the input. Love ls1 tech!