WPG

Hi everyone, new to the site having trouble with my 1997 z28 w 6spd. In closed loop the car surges at rpms below 2200. Had this before some dtcs showed up, they are p0101(maf sensor circut, p0300 random misfie, and p1416 bank 2 secondary air injection). I checked fuel pressure and comes up to approx. 42 psi but quickly begins to fall I think fuel pump is on the way out, also hard to start when it sits awhile any help eould be greatly appreciated, thank you in advance.

Injuneer

I'm going to move this to the “LT1 Based Engine Tech" forum. Better place to get the help you are seeking than here on “New Member Intro".

P0101 is telling you there is a large discrepancy in the MAF sensor reading, when compared to the mass air flow calculated using the speed-density method. This could be due to vacuum leaks, a leak between the MAF sensor and the throttle body, or a faulty or dirty MAF sensor. The speed-density calculation could be “off” due to problems with the IAT sensor or MAP sensor.

This condition may have existed well before the code set. The difference between the two flow readings (MAF sensor vs. speed-density calculation) has to get fairly large before the code sets.

P1416 is telling you there is little or no AIR system flow to the passenger side exhaust manifold. Could be a melted rubber elbow in the piping or a damaged check valve. A stuck closed check valve wouldn’t affect how the engine runs. A stuck open check valve could melt the rubber elbow, and will allow air to enter the manifold in closed loop, throwing the air/fuel ratio off on Bank 2.

How did you test the fuel pressure? Did you turn the key to “run” to prime the pump, and watch the pressure to see if it dropped? If that is the only test you did, it simply indicates the check valve in the pump is faulty, the fuel pressure regulator is faulty or a line is leaking. While the check valve in the pump will cause hard starting, once the engine starts, it would not be a problem.

Did you check the pressure at idle, with and without the vacuum compensation line attached to the fuel pressure regulator? Did you drive the car under heavy throttle/high RPM with the gauge taped to the windshield?

WPG

First off thanks for your response, I didi write back dont know what happen. I checked fuel pressure while driving (tape to windsheild) gage went up and down depending on load, all seemed normal. At full throttle the car feels like it hit a wall, rpms climb very slow as well as speed, also had a bunch of smoke from underneath. I beleive the cats are a problem, could this cause the misfire code as well as the one for 2nd air check valve. Thanks for your help.

Injuneer

What are the engine mods?

The fuel pressure should hold at least 40 PSI at WOT above 5,000 RPM.

WPG

Yes fuel pressure was above 40 psi, but the would not acclerate quickly at all, alot of noise but no speed.

WPG

Only mods are K&N cold air intake and abjustable fuelpressure reg, and MSD distributor. The car has 249k miles was running great prior to this happening. The car has no power at wot, fuel pressure is fine but very dlow to gaiin speed. I think maybe cats are a problem. They are direct fit magnaflow cats.

WPG

Car is mostly stock except for K&N air take, MSD distributor, magnaflow cats(dirext fit) and adjustable fuel pressure reg. The car has 249k miles. Below 2200 rpms it stumbles and smoothsa littl eabove 2200, but at wot fuel pressure is fine but no power at alll. I think the cats, itwas running fine then out of clear blue slight surge at cruiseing speed, then got a little worse and alot of rattleing from the exhaust. Now this is where Im at.

BTC

Do you see any metallic shavings coming out of the exhaust? In my experience, that would be indicative of collapsed/collapsing cat/s.

Injuneer

When was the MSD Opti installed? MSD just has one problem after another with that thing. Units produced in the last two years are prone to causing surging at idle.... numerous people with the problem. I actually sent MSD engineers (thru one of their techs on another site) a data log showing exactly how erratic, irrational signals from the optical cam position sensor (up to 7,000 RPM, when the engine was actually idling, with 0% throttle) were causing the PCM to ratchet the RPM up and down using the IAC motor. The problem was traced to the optical module they were using, and high voltage interference from the cap. They claim the problem has been fixed, but that was only a couple months ago.