Hi !

I am new to the forum so "HI" everyone. I bought my second Corvette this summer which is a red Corvette 1987 with only 35 miles on it (previous one was a 1981). Looks new inside and out. However, it has its age so it needed some repairs. The problem that I have now is that it's hard to start when hot if parked for more than several minutes. I think that it was like that when I bought it. When cold, it starts right away. When hot, after one or two minutes, it starts right away. Then after 10-15-20 minutes, it takes like 5-6 seconds to start. Pushing the pedal to the metal when starting doesn't improve the situation so much.

This is what I did to the car so far (by myself) :

- Spark plugs and wires
- Rebuilt the distributor (it was a about time, the rotor was barely touching the stator)
- Changed the injectors for Bosch III flow/pressure match
- Checked the injectors resistance cold and hot : ok
- Checked the injector connectors with a Noid Light : ok
- Changed the Valve Spring Seals (bog smoke at start up - solved)
- Changed the head gaskets (were not leaking but since I was doing the valve spring seals)
- Changed the outside bottom window seals (was cracked. old rubber)
- Changed the Pressure Control Valve valve (PCV)
- Changed the Exhaust Gas Recirculation valve (EGR). The old was good. grrr.
- Changed the Fuel Presssure Regulator valve (FPR). There was a gas smell in the vaccum line and changing the FPR solved it.
- Changed the Coolant Temperature Sensor (CTS). The old was good. grrr.
- Changed the fuel filter.
- Delete the 9th injector (which was tested bad by a specialized shop)
- Changed the rear differential seal. It was spraying/spining oil everwhere !
- Used ATP AT-205 to stop a transmission leak (it worked - Thanks Scotty Kilmer)
- Changed all fluids on the car.
- Changed the transmission oil pan and filter.
- Checked the compression on all cylinders (dry) : ok around 150 psi.
- Checked the Mass Air Flow (MAF) resistance and voltage : ok
- Checked the Trottle Body Position Sensor (TBPS) resistance and voltage: ok
- Checked leaks with TB cleaner : ok
- Checked Air Filter : ok
- Checked the Rail Fuel Pressure : not sure that it's ok !

Here are the Rail Fuel Pressure measurements after priming the car (key to on without starting) and then turning the key to off.

T 0 min : 40 psi
T 5 min : 30 psi
T 10 min : 27 psi
T 15 min : 25 psi
T 20 min : 23 psi

The fuel pressure decay was worse or the same before I changed the injectors and deleted the 9th injectors. I noticed today that my rail pressure port tester was leaking but it shouldn't affect the rail pressure reading since I am basically sealing it when measuring the pressure. I haven't tested the fuel pressure with the engine running but it works perfectly fine when started. Maybe it idles a little rough but it's subtile.

I did some reseach and an article was talking about "vapor lock" and "fuel pressure check valve"... Vapor lock is fuel vaporization in fuel lines/rails. Fuel pressure check valve ? I don't really know what to do with that. Replace the fuel pump ?

I haven't check my O2 sensor but I don't think that it could make that symptom.

I am running out of idea here. Maybe someone could help me find the issue ?

Thanks Guys !

Steve

 

Been fooled by good readings at idle
If your hose is long enough tape it to your windshield, put a load on the engine and see what happens
Wonder if you have leak in one of the fuel pump lines? Takes a few minutes to pull it out. Keep the key off!

 

Thanks CV67

I will try it tomorrow and see what kind of pressure I get when the engine is running. The car smells gas at start-up and even after so it might be part of the explanation. But there is no obvious gas falling on the ground. If there is a leak, it would be very small. Would it be possible that some gas are returning in the fuel tank ? I noticed the other day that when I removed the gas cap, there is some pressure build up in the gas tank. Can it provide some insight of what the problem could be ?

 

Find it strange that you removed the cold start injector as it name implies it provides additional fuel during cold starts although you're not having cold start issues. Did you switch to an '89 PROM as that year the CSI was deleted.

 

No because I was told that the car will be fine if i drive it only in the summer. It starts well when cold

 

If your oxygen sensor is more than 24 months old (or 50k miles) it is time to be replaced. The old OBD1 Corvettes used the inexpensive 1 wire oxygen sensors. If you have one that is flat dead it puts the Corvette in limp home mode.

The big three for the EFI system are your Oxygen sensor, your Coolant Temperature sensor and the MAF sensor.

Replacing your Oxygen sensor should be part of your regular maintenance on a C4 Corvette. The part is inexpensive and makes a big difference in the economy and performance of the Corvette.

 

Thank you ctmccloskey. I agree with you and I will do it. I looked at mine today and it's rusted and all. Probably the 33 years old original.

I eliminated any fuel pump related issues to my problem tonight. I pinched the return lines going at the fuel pump and there is still a steep decay in fuel rail pressure after priming the car. No fuel leaks anywhere that I can see or smell. The vaccum line from the FPR is not smelling gas. The connections to the fuel rails are dry. there is no fuel dripping from anywhere. The pressure to the fuel line is always 40 psi after every turned "on" key then it decays quickly. If I start the car, the pressure is steady at 38 psi. If I rev the car, the pressure does a quick bump than goes back to 38 psi right away which is normal.

Here is my official conclusion and it's not fun. One or more of my new Bosch III injectors are leaking. There is no other possibilities that I can think of. It's frustrating because these injectors are expensive and they are a pain to replace.

Now, what should I do ? There is a place nearby that is specialized in injectors. They will fully test any for 35$ bucks with a complete report. If a get them all tested it's gonna be 280 $. I bought them from a reputable seller (not Ebay are Amazon). Will they pay for that testing? If they give me a new set, will they be good this time ? Should I have them tested before the installation. They should be good from the get go, damn it ?!

But thinking about it, what are the chances that my original ones were bad and then this new set is bad too. I am questioning myself on the cause. But what else could it be ? I did all the tests and it could only be that ! It's like I threw 400$ in the thrash and I will need to pay another 280$ to get them tested ? Not fun at all.

What you guys would do ?

 

I searched and below 35*C is when the CSI will provide additional fuel during start. To give you additional insight, I looked at the tune in a stock 87, at 20*C ~14% additional fuel at crank, 32*-80*C ~12% and 92*-116*C ~5% so yeah allegedly no additional fuel from the CSI at startup. On my '90 with the Bosch IIIs, I noticed that at any temp, key on, fuel pump relay clicks off, key to crank, windmills for ~3 seconds then roars to life. Immediate shut down and restart is instant. Let it sit hot 15-20 minutes and it would be back to the ~3 second crank. I increased the pulse crank multiplier in the tune and it starts almost instantaneously after the starter engages. Oh btw depending on how much you had your foot on the accelerator pedal, does nothing for fuel injected engines during startup. If anything, 2.4v+ at the TPS enables clear flood mode and the ECM won't pulse the injectors. There's no accelerator pump on the throttle body so stop pumping the pedal like you would on a carburetor.

 

Have you pulled the vac. line from the FPR to see if you can smell gas, indicating a failed diaphragm?

To check for an injector leak you can pull the spark plugs to see if any are fuel-loaded.

 

Yes, I've pulled the vac lin from the FPR. It's fine. No gas smell and the fuel pressure increase by 10 psi when the vac line is pulled out.

When would you recommend to check the spark plugs ? If an injector is leaking, my understanding is that it's gonna leak on the intake valve once the engine is stopped. If the intake valve is closed, there won't be any gas smell on the spark plug, right ? Or should I turn the crankshaft by hand for 1 turn before checking ?

 

Update ! Solved.

One of my NEW Bosch III injector from Corvettedepot.ca was Leaking !! I had them checked at a specialized shop today. One of them was leaking badly. I am thinking of uploading the video on Youtube and then post the link here. Not sure if this is allowed though.

So, I tried to solved my issue with the original leaky injectors with brand new ones but the new ones had a leaky one too !!! How fun is that !

Fortunately, they owner of the shop just asked me 15$ for this verification which was too sweet from him since he normaly charges 35$ per injector to fully test them. I tried to call Corvettedepot today but I only have been able to leave a message.

I am happy to have rightly diagnosed the problem but at the same time I am frustrated by this lack of quality.

I would STRONGLY suggest to have your new injector tested before installing them on your car. With a repair that will take you hours to perform, you better make sure that the parts are good. Or you risk to do it again like I did. /%/?$""

Here are some pics from the video. The faulty one is # 7. The light was burnt on the tester for # 6.


Leak with pressure on 1

Leak with pressure 2

Leak while running

 

Here is the link to the video

 

It's been a while but I just wanted to add that I had put a good old injector to replace the new faulty one and it solved the issue completely. Now, I don't even own the car anymore. Hopefully, this post will help some people in the future...

 

So after all .... the bad warm start was caused by leaking injectors ? Not the O2 sensor, CTS or 9th injector ?
Im facing the same issue

 

Exactly !

 

Thank you !

 

IS that a typo? Does it really only have 35 original miles?

 

who did you get to test your injectors? I know this is a old post but I'm having the same problem and I have changed and checked all the things you did.

 

I'm having the same problem. did that solve you problem as it did 87redrocket?