lostcobra

Originally Posted by lostcobra
I have an 1984 Corvette that has a cold start problem. To start the car it normally starts on the third crank of about 5-6 seconds, while pumping the gas the entire time.
i have replaced the plugs, cap, rotor, fuel filter, o2 sensor, fuel pump relay,
the car runs good after it gets warmed up. It does smell like it running rich because its a little stinky with exhaust. I've talked to a couple of shops and they seem to not want to work on it, because they aren't sure it would take 8-19 hours just checking it out and not sure they can fix it. I need to do the work myself(with my Dads help). I know there's someone out there that can tell me whats wrong with it. Whats the best service manual for this corvette?

When I turn the key to first position(not start) I do not hear the fuel pump pressurize like on my truck. When cranking, it take 3 crank of 5-6 seconds and it barely starts throwing fuel into the throttle body. When it finally starts it sprays and idles to warm up good. It seems likes it taking longer and longer to start.

Cliff Harris

The ECM turns on the fuel pump for 2 seconds when you turn on the ignition key. It then turns off so the fuel pump won't run if you turn on the ignition but don't start the engine. The will then turn on the fuel pump when it sees reference pulses from the ignition module inside the distributor. I feel like I've type this a million times... ;-)

If the fuel pump relay doesn't work for whatever reason, there is an oil pressure switch that turns on the fuel pump when the oil pressure reaches 4 PSI.

Whenever it takes a lot of cranking before the engine starts the prime suspect is the fuel pump relay. If it doesn't pressurize the fuel lines then the oil pressure switch needs to turn on the fuel pump. It usually takes a bit of cranking to build up the 4 PSI of oil pressure.

Check you fuel pump relay. They are cheap enough that it's often easiest to just replace it instead of doing a lot of troubleshooting.

occupa

Is the check/service light blinking?
My was extremely difficult to start and would not run right until the coolant temp was over 130 degress.
Extremely rich start smell like is was flooded.
The coolant sensor had failed in a open circuit condition and according to the temp chart the ECM thought it was -40 degrees
Code 15 if yours is blinking.
I guess newer ECU go to a default condition in the event of malfunctioning sensor.

lostcobra

Thanks, i have seen your post and thought WAMO, i'm about to fix it. I replaced the relay, but i guess the relay could be bad, because it didn't help. Logically it sounded great. I had every light in my garage on looking for the coolant sensor, I'm going to try again to find it then replace it.

I dont want to replace the entire fuel pump assembly especially if its working fine but I'm not sure. I listen and it does not sound like it comes on for the two seconds it should to pressurize the lines, so your secondary cranking to get 4 psi sounds good. It you tore your out would you go ahead and replace the entire sh**ery.

fredd1

The coolant sensor is located at the right front of the engine block next to the idler pulley bracket -see page 6E2-7 of the Helms factory service manual (the most comprehensive manual -you should get one).

The manual also says if it's difficult to access the sensor (which it is) you can check the resistance between terminals 4 & 11 on the black connector going to the ECM.

occupa

For the fuel pump Pin G on the ALDL connector will turn on the fuel pump. Connect to +12.

Paper clip or 14 gauge solid copper wire works in the connector

However, is extremely difficult to put a fuel pressure gauge on the system.

So listening may be the best bet.

Cliff Harris

You can force the fuel pump to come on by disconnecting the oil pressure switch and shorting the contacts of the connector together. I used tweezers. It's located on the rear of the engine block behind the distributor. It's easy to see back there and has one orange wire and one red wire coming out of it. The orange wire is hot all the time, so you don't need to turn on the ignition to do this test. The connector is held on by a lock ring, so you have to unlatch the lock ring in order to get the connector off:

74 LS4-454

Hello, happened to look in the C4 section and saw this thread. In addition to what has been said, would like to have you look at our "sticky" in the C3 Tech Section. Link is posted below and hopefully will give you additional tips to what has been stated. In the BOOKS & REFERENCES Section, you will see a list of materials suggested to own and read. IMO, the Shop or Service Manual for your year is the best to own, may take a little time in understanding it, but supplies a wealth of info on troubleshooting & correcting problems. Hope this helps.............................Tom

http://forums.corvetteforum.com/c3-t...solutions.html


FWIW, with my 82 which is my "dd", I have never had to pump the accelerator during start-up to get the engine running. I turn the key on and wait for the pump to run for 2 seconds and then fire the engine up. Yes it will take about 5 seconds for the engine to start during your first start-up of the day. To me, this is just how the CFI operates. After it starts I will bring up the r's to over a 1000 or more and then the fast idle comes on. On my first start-up of the day I let the engine warm-up 3-5 minutes (depending on outside temps) before driving down the road. This way I don't have any stumble or hesitation as I drive off. If I am doing local things, and getting in and out of the car, all I do is turn the key and restarts are instant.

I have also added this thread to the "sticky" in the appropriated section to help out owners in the future.

lostcobra

I've dug into the engine a looked at all the post but I cant seem to find the coolant sensor and I think its under all the smog and air flow devices, can anyone tell me how to get to the coolant sensor?

What does the coolant temp sensor have to do with not starting right up.

Tom400CFI

The coolant temp sensor is a major player in the ECM's "decision" in setting the fuel delivery; at start up and while running. If it is giving an erroneous signal, the fuel delivery could be off, making the engine hard to start.
The Coolant temp sensor is located at the front of the intake manifold; shown here in this drawing, under the smog pump;



And also in this photo...

lostcobra

OK FOLKS, I now have a perfect running 1984 Corvette again, but I cant take credit for it. I called about 20 shops and no one really wanted to work on it. I finally found a shop with a guy who broke his arms (teeth) working on Chevy's back in the 80 for Chevy Dealers. He didn't hesitate to work on my 84 C4. They fixed the stinky exhaust smell, the hesitation, the hard start, leaking coolant line, sticky hard open door and Id'ed about 3 more minor things for me to handle in the future.
The owner told me the hesitation was from an old leaking vacuum hose to the MAP sensor next to the starter relay. I had already replaced the Starter relay but he said the pin in the connection were loose, they tightened them up and got good contacts and fixed the hard start. The fuel pump was bleeding down after starting and was part of the problem so they replaced the fuel pump. replaced a leaking hose by the distributor to end my coolant leak, Lubed the doors with WD40 and air blew out. 100% difference all around.

The total cost was $398.00 out the door, and I was ready to spend $1500.

I hope this helps someone out there trying to trouble shoot your ride.

Thanks to everyone who took the time to read and give tips.

Tom400CFI

I'm glad that I took the time post pics so that you could diagnose and fix it!