Remington James

I bought a 1996 z28 it had a 396 stroker in it. It is running very lean then when I stomp it it cuts out really bad. We ran a fuel pressure test and it came back 40psi and at wot it dropped to 30psi. I believe this is my issue is my fuel pump. This vehicle has a electric fuel pump in the tank and a inline electric fuel pump also. What are some things I can check to see which in every is bad or should I get a new fuel pump in the tank or just run a inline electric fuel pump. Thanks for the help.

JakeRobb

In general, I'm against just replacing parts to see if it fixes the problem. That's a great way to waste money. Take the time to diagnose the problem properly, or to pay someone who can.

I don't think I can help you diagnose, but I think the people who can help will be better equipped to do so with some more information about what's in the car.

Do you have the brand/model for either of the fuel pumps? Do you know what size the injectors are? What heads and cam? Still running the stock PCM? Do you know how much power it made when it was last running right?

All of that info will help determine how much fuel the engine requires, and how much the fuel system is equipped to provide.

My not-so-educated guess: the inline pump is bad, or isn't getting good voltage. If you have a meter, checking to see that it's getting power would be a good first step.

I infer that the car has an in-cabin fuel pressure gauge. Right? Any chance it has another one hooked up before the inline pump? It would be nice to know how much pressure you were getting from the in-tank pump.

Oh, and check your fuel filter.

Welcome to CamaroZ28.com!

Injuneer

You have to check both pumps. Have you verified that the inline pump is even running? If it isn't, it's reducing flow and causing the pressure to drop. Is the in tank pump stock capacity, or upgraded? How old are the pumps?

You can't run with only an inline pump. If you want to run an outboard pump, the suction needs to come off the low point of the tank, and needs a minimum of a -10AN suction line. If your engine requires more than you can flow with something like a Walbro 255 LPH pump, the best solution is a dual in tank pump setup.

Remington James

Alright so I changed fuel pump inside tank and took out the inline pump. The car runs better but is still missing and running lean. I'm going to check my plugs tomrrow what is every gapping there plugs? And other leads y'all think

Injuneer

Did you recheck the fuel pressure? What size pump did you install in the tank? Is the pump running on an upgraded wiring setup (e.g. - hot wire kit)? What is the flow rating of the injectors?

Stock plug gap is 0.050". What is the static compression ratio? Are you running a stock ignition - Opti and stock single connector coil? Does it have a MSD box? If the compression ratio is higher than stock, you should be running 1 or 2 steps colder than stock. You can go as low as 0.035". All depends on the total system. Note the condition of the old plugs when you pull them out - signs of running lean, burned electrodes, excessive gaps, running rich, etc.

Have you scanned it for codes? A scanner with GM Enhanced Parameters can pull up the misfire count by individual cylinder. That can give you a clue as to whether there is a specific cylinder missing - bad plug, wire, injector or compression - or whether they are all missing at random indicating a systemic problem, 2 cylinders indicating crossfiring due to bad wires, etc. Check the wires for header burns, old age, etc.

Have you checked the rubber intake elbow for cracks or tears, or the bottom of the elbow not being fully over the throttle body? Has the MAF sensor been cleaned?

Remington James

Alright guys so been data logging all morning and my car will not close loop and when the loop is open the o2 sensors are not fluttering they are just in 0. Then when we close the loop it runs great like it suppose too. And idea what it could be? That makes my loopbstay open

Injuneer

Three things have to happen for the PCM to go into closed loop:

- pre-cat O2 sensors have to get hot enough to work (~600°F). When the engine starts COLD, the O2 sensors should read about 0.450 volts (= 450 millivolts). Sensors aren't working, you are seeing the PCM bias voltage. As the sensors start warming up, they will move away from 450 mV, dropping toward 00X mV if you have a working AIR pump, or rising toward 9XX mV with no AIR pump (reflects enriched A/F ratio for cold start). The scanner should be able to pull up the flags for left and right "O2 sensor ready" when they are warm enough.

- coolant temp must reach a programmed value, at least 120-140°F (varies with year and other conditions).

- "timer" must time out. Typically 206 seconds from key start.

Remington James

How do I check o2 sensors?

Injuneer

You indicate you have "been data logging all morning", and you indicate the O2 sensors are "just in 0" (whatever that means - might want to clarify the readings in millivolts). Look at you data log and compare the data to the three criteria I listed above.

If you can export the data log as a.csv file, I can review it.

At some point, if you want help, you are going to have to answer the questions we have asked. So far not a lot of answers.