KenMathisHD

Howdy howdy
I've been having problems with hard starts in my 94 LT1 for a while. It'll take a few cranks of the key, anywhere from 2-4, for the car to start when cold, and 1-2 tries when hot for it to start.
When it's cold, it'll start to catch and sputter on about the second try. Sometimes if I keep the key turned while it catches and sputters I can get it to turn over, but usually I'll have to cycle the key for another try. And very rarely, she'll turn over but her idle will drop to about 400-600rpms and the car shutters pretty badly, and then dies.

I hooked up a Fuel Pressure gauge to the point before the regulator and turned the key to on to see what I got. It gave a slight twitch of the needle, maybe registering 1lb, but nothing more. Curious, I kept cycling the key on and off without cranking the engine, and finally got it to jump to 10lbs on the 3rd cycle. After that, another key cycle would jump pressure up to 20, 25, or 30 for about 1-2 seconds while the pump cycled, but would drop off right after that to 10lbs and then drop to 0 after about 1-2 minutes.

I replaced the filter to see if there was gunk in the filter that was causing the pump to strain to push pressure past that, and the regulator since it, like everything else, is probably the part that rolled with the car off the factory floor. While the bay has a shiny little part to look at now, it still starts up rather hard.

While running, pressure comes up to and stays at about 32lbs, though this is in park. Every few seconds, she has a little twitch while standing still and seems to vibrate a little more than I like. I've got plugs and wires coming for her to attempt to remedy this and the Opti and coil were replaced about 4 months ago, but I'm wondering if this might have anything to do with her hard starts. She also seems to run noticeably rough when getting up to 80+ mph, though not sure if this is related or just how the car runs/drives at that speed

What I'm thinking next are leaky injectors or a bad/weak fuel pump, or bad seals somewhere, but I'm not sure how to test them. Any ideas on how to see what's going on with her?

Space387

I would be inclined to say go for the fuel pump. My Lt1 Firebird was acting similar and it was a pump fouled by rust in the tank. There is a long story about that but with as easy as it is to get into these tanks for a pump go for it.

TorchTarga94

Definitely sounds like a fuel pump and or fuel pump pulsator issue to me.

1993C4LT1

You do know the car has a Schrader valve on the passenger side fuel rail? 32psi running is correct. Low side, but still in spec. Do a snap throttle test when the car is running. The pump should go to about 40psi. I've had a hard start when warm and letting the car sit for a while on both my LT1s. Everything checks out fine. So I gave up.

KenMathisHD

On the rail or the line? I hooked up right at the valve on the line by the regulator, pulled 32 while running. Gave her a little throttle, though not a bunch, and pressure went up with the throttle, though the increase did seem delayed. If there are two valves, does the valve on the rail make for a better or more reliable reading?

Looking around, seems like there are folks ditching the pulsator in favor of a high pressure piece of hose. Does it hurt the pump or the car any if you ditch the pulsator? And is it in the tank or outside of the tank?

aklim

I'd pull the hose off the FPR and turn it to run but not crank and see what it comes up to instantly and how long the pressure holds. If it is anything like the L98 it should come to 40 psi and hold for hours. Not sure if there are 2 valves. Pulling the hose simulates WOT conditions. If it tests good, I'd take it for a drive with the gauge taped on the windshield and see what it does at WOT with a load. It might be ok down low but cannot keep up.

Doesn't hurt anything. When the rubber gets old, it might leak and you lose pressure. It does nothing so why not get rid of it? Racetronix makes a kit but you can get it for $30 or get the pump and it will have the kit if you need a pump.

KenMathisHD

Aklim do you mean pull the vacuum hose off the FPR and test at the valve, or pull the fuel line and test at the line opening?

Also, for the pulsator, where on earth is it? I’ve got the AllData subscription for the vette but it’s suprisingly difficult to find specific info on the pulsator, lots of info on pretty much everything else but I can’t find anything on the pulsator. Is it in the tank or outside, and if it’s in the tank then how on earth do I get the thing out?

aklim

I wouldn't test anywhere but at the schraeder valve. You pull the hose off the FPR to simulate a WOT. Ideally you want to see it rise up instantly at the prime and hold for a while. If it doesn't you have an issue to look for but we'll circle back if that is the case. If it is still good, tape the gauge to the windshield and go for a run. Do a WOT run and see if the pump can keep up.

It is in the fuel pump assembly. It looks like:





It is on the pump assembly which looks like:

KenMathisHD

Hose that came with the pump next to the pump for comparison
Everything that came with the pump
Ok, so when I pulled the hose from the FPR and keyed on, no crank, pressure shot to about 30-32, and then once the pump stopped going it dropped to 0 within a second. Repeated this a few times just to be certain, and got the same result each time.
Then took her out on a drive for some errands and hoonin. Once she got all warmed up, I did some WOT runs. Got it in slow mo and normal speed, and looking at both it seems when I mash down on the petal, the pressure will momentarily spike at about 34-36, the needle will wildly jerk between 30 and 36 for about a second, and then goes down to about 26-27 until I let off the throttle, then it’ll go back to 30. Did this a good 4-5 Times and the result was the same each time, didn’t feel weak going up the RPMs though, it pulled pretty well and I may have set my new 0-60 speed record

While starting her up after coming from the bank, I got the pressure reading of the wonky lazy start she’ll do where she runs like crap for a time. It was real brief and she smoothed out real quick, but while she was running like crud the gauge needle was slowly creeping up from 10, and she started running smoother when it hit about 29-30 and stayed there

Maybe it’s a combo of a weak pump and a bad pulsator? I picked up the pump from AutoZone, oddly enough they don’t even have record of a pulsator for a 94 vette. There was a little piece of hose that came with the pump, I’m assuming this is to replace the pulsator, but I’ll post up a pic of it just in case. Somehow they had the pump but not the strainer, so I guess I won’t be putting the new pump in today.

Looking at all of this, what do you guys think is up with this or what should I look at next?

haxxx

With the hose off the regulator you should be getting about 45.

I honestly have no idea what the fuel pulsator is even supposed to do but it doesn't need it. Just make sure you clamp the hose that eliminates the pulsator well. Someone replaced mine before I bought it and didn't even use clamps. Explained why I had about 20 psi...

If the regulator is original you may want to replace it. It will start to leak when it goes out.

KenMathisHD

It was one of the first pieces I replaced in regards to the starting problem. Maybe the new regulator is faulty as well?

Also, when I pulled off the boot at the filler neck of my fuel sending unit, I noticed that the connector from my sending unit only has 3 wires leading from the unit, but there are 4 wires coming from the cars harness. If somebody before me replaced the unit incorrectly and misconnected the lines, is it possible that that would cause the problem? I’d switch them around to play with it but I’d rather not connect them incorrectly myself in case they’re ok where they are

haxxx

If you replaced the regulator, unlikely. The pump always run at max, and the regulator uses engine vacuum to regulate by sending fuel back to the tank, which will drop the psi. By pulling the vacuum hose you are closing off the path back to the tank which should max out your psi, which is about 45. Clamping the return line should have the same effect.

Your wires are fine, it will either work or it wont. Since you have the new fuel pump already just go a head and change it. Eliminate fuel pulsator by using the line provided and clamping it down on both sides. If you haven't already, get a new filter 'sock' for the end of the pump, it's like 5 bucks.

aklim

Start with crimping lines or replace the car altogether. Your call.

L.V. Vette

Wow! Replace the car? Lol If pressure is dropping that much that quickly, there is a massive fuel leak.

aklim

If you are going to guess what the problem is and replace parts, might as well do the whole thing all at once. You need to start crimping lines. To narrow down the problem other than aged broken parts or worn out parts.

L.V. Vette

Interesting, never thought of that way. Makes sense now. I like the way you put it

aklim

It's cheaper and less aggregation to dump the car for a newer one than to keep throwing parts at it.

L.V. Vette

True but this one just looks like a fuel pressure issue. OP need to clamp down fuel lines to help isolate location of leak

aklim

Absolutely. Since it is all there at the fuel tank and you remove a few torx screws, it is super easy. Assuming it pressurizes instantly, crimp off the return line, and see if it holds. If it does, try again the next day and see if it holds without crimping. If it doesn't we know the problem is north of the crimp, IOW the pump, the pulsator, the injectors or all of them.

Just throwing parts as a guess is going to fix the problem only if the SWAG is lucky.

KenMathisHD

When I clamped off the return line, the pressure still plummeted when the fuel pump shut off. So injectors, pump, or pulsator

Since I already had the pump and he replacement hose for the pulsator, I pulled the assembly and replaced both pump and pulsator. I was surprised when I saw the actual size of the pulsator, not much bigger than a few jelly beans.
Unfortunately, while unbolting the assembly from the tank, about 4 out of the 9 bolts snapped, even after using penetrating oil and being real careful with them. Got some more bolts from a local hardware store to replace the ones that didn’t snap (M6 with some large washers fit), but I think some point soon I’ll drain the tank and see about drilling the old bolts out

Once it was all back together, I cleaned up round the area and cycled the key to on, and was happy to see the pressure jump up to about 40-41psi and hold. I think it was the first time she fired right up since I bought her back in April. I’m still probably going to replace the injectors with some shiny new ones, get some new ungunked ones in there and have some as backups/spares once they’re cleaned.