I have an issue with my C4. Just replaced fuel pump and sending unit, hoping that would correct the issue with not starting. It turns over but that is the extent of it.

Im guessing spark is next but not sure on where to start on testing that.

Any help would greatly be appreciated.

 

Pull any spark plug wire. Put a spare plug in the wire and ground the threads to metal on the engine. Try to start. The plug you are holding should spark. Check for codes. You can buy a code reader for peanuts. Also, borrow a fuel pressure gauge from a box auto parts store to confirm the new pump is working. Dan

 

Like Whaleman said, check to make sure the new fuel pump is working with a pressure gauge. Also what year C4, L98 or LT1 will help with responses that can help with troubleshooting. With these cars it is important to troubleshoot and find the issue because throwing parts at C4s hoping it fixes the issue can get costly.
Did you start down this path due to car not starting, or because of some other issue?

 

So - to make any Internal Combustion engine run - you need three things:

Fuel
Spark (at approximately the right time)
Compression

So - as Whaleman suggested - First - check for spark at one of the plug wires. Pull one of the spark plug wires (#4 cyl is typically one of the easier cylinders to get to on LT1 engines) and use an insulated tool to hold the wire maybe an eight of a inch from a grounded part of the engine/car, and have someone crank the engine over for a few seconds - you should see a spark jump from the wire to the ground. Alternatively - you can disconnect the plug wire, grab any old spark plug, and insert the terminal end of the plug into the wire, hold the threaded side of the plug against something grounded,and have someone crank the engine over for a few seconds - you should see a spark across the spark plug gap.

You said you changed the fuel pump - I assume that when you turn the Ignition key to the Ignition On position - you hear the pump run for a couple of seconds - if not - that's a problem and probably the cause of the no start condition - but even if you do hear it run - still hook up a fuel pressure gauge to the fuel log, and check the pressure (if you don't have a fuel pressure gauge, some chain auto stores have a tool borrowing program).

Let us know what you find.

 

This is a 1986. I originally was having issues with idle, so parked it and now getting back to it. Replaced it and then figured it wasnt starting and researched and all pointed to fuel pump. I decided ti replace both the sending unit and pump. FAst forward and still doing same thing. I do hear the fuel pump when turning the key to on. I figured I would also order a fuel filter as figured it wouldnt hurt. Also ordered a fuel pressure gauge so I would have one.

 

 

Lots of good advice. If you have a timing light use it to check spark It's quick and easy

 

I do have a timing light, how would I go about testing with it?

 

Wow nice info. I will take a look. I do have the service engine light on when starting so theres that, so will see if I can follow this.

 

Just hook up as normal then start car. Should see steady light. Go from wire to wire.

 

Ok so busy day today. I replaced the fuel filter, and then tested the fuel pressure. The fuel pressure is steady at 0 lol. WTF?

I also checked spark at one of the wires and it was sparking. I am still in the process of replacing the plugs though. I still have 2 that I cant seem to get to very well and its causing me a little sanity.

im guessing I still have issues with the fuel delivery. When I took the pressure gauge off the port, there was a tad bit of gas there but not much.

Let me also tell you that the sending unit didnt have exactly the same plug to plug into the harness so I cut off the new one and replaced it with the old one. im hoping that the wiring is the same.

Is there a way to test the fuel pump further, i,e. voltage. When I turn the key on, I hear what Im guessing is the pump.

How long should it take for a fuel pump to start sending fuel to the front of the car?

 

It should take about 1 second to build pressure. Have you checked the fuse? Dan
so how do you check if the fuel pump is running again? - CorvetteForum - Chevrolet Corvette Forum Discussion

 

Hmmm. No sure haven't. Would that be under the hood or inside the car?

 

Fuel Pump Fuse Location - CorvetteForum - Chevrolet Corvette Forum Discussion

 

While I do understand that this is frustrating - you are making progress. You are now 99% sure that the no start is due to a lack of fuel.

There is a way to test further, it involves basically running the fuel pump. There are several ways that can be accomplished. Powering it by bypassing the fuel pump relay is one. In the case of the later C4's (the LT1 cars) you can power it by pulling the oil pressure sender connector and jumpng a couple of wires, or I believe that you can put 12 Volts on the load side of the fuel pump fuse (I don't have the wiring diagram for the earlier (TPI) C4's but I's sure others here will.

So - as whaleman said - you should have pressure to the fuel port in a second or two... So - if that's not the case - I'd suggest pulling the fuel pump, disconnecting the wires, feeding power to the pump, and checking power with a test light (don't use a VOM - they doesn't pull enough current to let you diagnose a marginal connection).

 

Had a great time replacing spark plugs this weekend, haha just kidding. Still cant get #2 in I guess is what it is. I purchased a thread chaser since it appears got a little damage on the plug, so we will try that next.

I would love to test the fuel pump without pulling it back out if possible. What is a VOM?

 

volt-ohm meter

 

One thing I will also say is that the wiring harness on the sending unit wasn't exactly the correct one to lien up with the car harness, so I cut the wires off the old harness and connected to the new sending unit. they weren't the same colors either. i just did one for one the way it looked, i think it had pink, tan, and black. and the other one purple white and black.

 

OK so good news. I took the sending unit and fuel pump back out of the car, and found that when i had put it in at first, must have somehow pulled the wiring off the sending unit. So stupid. Anyways I got it plugged back up and verified everything and stuck it back in the car.

Hooked up fuel pressure gauge and now fuel pressure now reads at 40 when turning the key to on. Pressure stays when key is turned off. So finally that works.

I have the charger on at the moment but still turning over but not starting. It did try to start a couple of times but that was about it. Im hoping after a good charge, it will start back up.

 

is it not good if the light flashes when testing the wires. They all flash when testing