Hello. Me and my friend are trying to work on his car and needed help, here is some info

Car: Z28 LT1 Automatic. New Fuel Pump, Cone Air Intake, New Water Pump, New Head Gasket, MSD OptiSpark

Problems: Car Struggles to start but stills starts accompanied with a gassy smell. Backfires when tapping the peddle in high RPM (If that’s normal)

Tried Solutions: Tried fuel additive, Changed Fuel Pump, Changed Coolant Temp Sensor, Changed OptiSpark (Rebuilt MSD Cap and Rotor Only)

BackGround on the Problems/Symptoms (Buckle In) (Events are in Order)

Fuel Additive, New Pump, and New CTS
Story goes, friend starts to have a struggle on his startup so he tries a fuel additive which to what he says “Helped a lot”. Begins to struggle starting up again accompanied by a multiple random cylinder misfire to which pointed to the Fuel Pump. We cut a “Trap Door” in the rear and changed the Pump, instantly starts up and drives fine. 2 Weeks later, begins to struggle again, we change the Coolant Temperature Sensor, no change at all. Problem gets worse with cranks taking as long as 6-8 seconds but still starts up. We then notice a pattern if the car is not started up for 20-40 minutes or longer (Hot) then it will cause the car to struggle, but if started sooner than that, it will turn on Instantly. Every cold start is like that as well as a gassy smell when it finally does start up within 6-8 seconds.

Fuel Pressure Check
We check Fuel Pressure, hearing it prime, we know it works with 40 Psi (Key On) and 50-60 Psi (Engine On) so there’s that, may need more info on that as I’m not sure what to look for in fuel pressure…

MSD OptiSpark Cap and Rotor
We bit the bullet and I told him to order a new OptiSpark to which he only ordered the Cap and Rotor *Sigh. Either way we put it in and test it with the rebuilt Opti on (Yes I Aligned it) (Note: This was right after I put the Opti in, no fans, pump, accessories, no intake, or the like was reconnected other than the Opti) and it started Instantly. We tried it about 2-3 more times to make sure and it started just like that. We begin to put everything together and we wait till the next day to add coolant so we take the car off from the jack stands

The next day, I add coolant and try to start it and struggles, dreaded I look up more info just to find out there’s this mode called “Clear Flood Mode” or CFM. So I try to start it normally to confirm it struggles and it still does so then I try to start it with CFM and it starts up way faster than just trying to crank it.

Solutions? Engine stall in reverse…
I’m thinking it could be flooding itself with gas somehow as the gassy smell is there and it easily back fires in high rpm, I’m thinking Leaky Injectors or bad Spark Plugs but what confuses me is that the car started up like Normal without any of the stuff on/connected then does this. So confusing and at a loss. Just recently, we were reversing into parking and he tapped the gas fast and the rpm’s went up and then died down and then proceeded to stall out…

Any help will be appreciated, and if any info is needed, I will provide more if so. Thank you…

 

What year is the car? 93 was different from the rest of the LT1’s. You mention Cap and Rotor only…is the rest of the Opti OEM or another brand? How old is it? Spark plugs: did you replace these? Are they gapped at.050? Have you pulled them since to see if one or more are fouled? You can also determine if one side is running lean or rich or both. O2 sensors: same questions as spark plugs. Plug wires…etc.

However, my suspicion would be a faulty injector.

 

50-60 PSI fuel pressure is way too high. Factory spec (with vacuum compensation line off the fuel pressure regulator) is 43.5 PSI (acceptable range 41-47 PSI). When you reattach the vacuum line the pressure should drop about 8 PSI below the no vacuum value. At idle, vacuum line attached, you should see about 35 PSI (stock cam).

Had the car been sitting unstarted for an extended period of time?

When the fuel pump primed did it reach at least 40 PSI before it shut down? After the pump shut down, how fast did the pressure bleed off? That helps detect leaking injectors, a leaking fuel pressure regulator, or a bad check valve in the pump.

What brand is the fuel pump? There are more cheap Chinese counterfeit pumps on the market than there are quality pumps. Spectra brand seems unreliable.

While the coolant temp sensor is new, did you do a complete check of the reference voltage on the circuit. If the PCM is seeing a lower than actual temperature, the cold start A/F ratio enrichment may be excessive. Read procedure below:

4th Gen LT1 F-body Tech Articles

Do you have the ability to scan the PCM?

And yes, year of the car is essential. There are too many subtle differences from year to year.

 

Apologies, I should’ve mentioned the year sooner. It’s a 1996 and I told the owner to order a whole new one and only ordered the Cap and Rotor which threw some concerns but we put it in anyway, the rest of the Opti is OEM when taken apart and not really sure how old it is as he bought it from a friend who bought it from someone who says it was sitting out for 3 years.

In retrospect, we should’ve checked the spark plugs but we didn’t, how easy is it to check those or take them off? The space in there is very limited and not sure where to start

As for the O2 Sensors, we didn’t check those either, I didn’t think it could be those but at the same time, it does make sense as the car does have a few issues fuel wise mainly being backfiring. Will work in that soon…

Spark plugs wires, I just bought the 7mm Altima brand as for some reason, cylinder 5 plug wire on the right (When looking at the engine or facing front of the car) was pulled right out of its boot that connects to the spark plug so it was just a small thread of wire going into the boot, not sure how that happened but we noticed as soon as the car began to misfire on its first drive after the Opti change. I changed that and again in retrospect, I should’ve changed the others as well, will get on that soon

 

Hi, is there a main Vacuum line I can check? When I checked the fuel pressure, all I did was connect the tester to the Schrader valve and nothing else. So when the car is put to On position, it goes to 40 Psi and so on, when the car is started, it ranges up to 50-60 (From what I remember, it’s around 55-57 Mainly). A thing I did notice is that after 5-15 minutes, the fuel pressure was down to 20 (Key Off) or that’s maybe the pressure testers dead zone for the needle but either way, it shows that it dropped after a bit, not sure if that’s normal or not. I didn’t really pay no mind to it as the car is supposed to always prime up to 40 anyway if I’m not mistaken but at the same time the fuel pressure dropping can be cause for a maybe gas flooded engine. Sorry My mind is all foggy about this, apologies

I have heard the car has been sitting for 3 years with a blown head gasket (Owned by a military personnel) and was sold to a friend who managed to start the car with a blown head gasket, then got it repaired by changing the water pump and head gasket and then sold to my friend to which I’m helping right now

Fuel Pump brand, I’ll ask him soon, he’s busy right now

I didn’t check that, I’m guessing I take the Voltage meter to the plug for the Coolant temp sensor and tell you the voltage? Apologies, not really good at electric stuff this deep.

and for the pcm, I’m guessing a code reader correct?

As for the year, 1996, apologies, I should’ve mentioned that earlier…

Edit: Just seen the procedure you sent, will look at it now

 

You put the fuel pressure gauge on the Schrader valve. Start the engine. You remove the vacuum control line from the fuel pressure regulator, or from the intake manifold nipple:

http://shbox.com/1/fp_reg.jpg

Hold a finger over the regulator end of the line or the manifold nipple to prevent a vacuum leak. Read the pressure gauge. Should be 43.5 PSI. GM specs accept anything in the range of 41-47 PSI.

While you have the vacuum line off, check the line for the presence of wet fuel, or a strong smell of fuel. That would indicate the pressure regulator is leaking.

While the engine is still running, reattach the vacuum control line. Pressure on the gauge should drop proportional to intake manifold vacuum. Gauge should read in the range of 33-38 PSI. If it reads 55-57 PSI, something is seriously wrong.

If the fuel pressure drops to 20 PSI within 5 to 10 minutes after shut off, something is leaking.

If the car was sitting, unstarted for 3 years with fuel in the tank, the injectors may need to be cleaned or replaced. The ethanol in current gasoline absorbs water and corrodes things.

You need a device (scanner) that can pull codes from an OBD-2 Powertrain control module.

 

I had a similar situation. If it was driven, shut off then restarted within just a few minutes, it would crank right up. But if it was driven, then shut off for a while, trying to restart would be difficult, as if it were flooded. Even the next day. But if it sat for several days, it would crank right up. I had the injectors "checked" and the shop said they flowed fine. So, like you guys, I changed a lot of stuff before thinking that the injectors might be leaking after shut off. Changed the injectors--problem solved.

 

Hasn't signed back in since his last post..... 11 days ago ? ? ?

 

apologies, I would definitely like to add more but friend says “Im too scared to mess with this stuff”, or “I think its the injectors” and proceeds to not tinker with the car and just runs the car the way it has been running through out the whole thread. Sorry everyone, id love to add more but I cant help someone who doesn't even want to help himself… until then