1988 c4 with L98.At steady speed between 30 to 70 constant surge.Checked fuel pump:43 psi key on,38 psi engine running.Pulled vac. line off PR and 48 psi and no gas smell in hose.
Also have a hot start issue-have to half depress acc. to start warm.Leaking fuel injector(s) ? Car accelerates fine under load (no stumble).Seems likely injectors or plugs.No prev. owner info,with 65k miles could be
original injectors/plugs.Starts fine from cold start.Any and all opinions welcome.

 

Do you have any codes? Does it hold its pressure after shut down. Should hold for a while. If not could be leaking injectors and/ or fuel pump. If you have Multitech injectors (light gray bodies) and have used ethanol gas in them, it could have ruined them. Kevin

 

fuel pressure gage drops within 5 minutes from the initial 43psi (key on) to 30psi with key off.Indicating leaky injector(s).This could also be causing the hot start
cranking issue (flooding) Does this seem to make sense ?

 

You could check/pull a couple plugs to see if wet from gas when hot and off. To confirm it’s the injectors

 

Scanner? If so, O2 and INT/BLN? Vacuum leaks. Auto or manual? Surge with cruise control? Cat converter partially restricted.

 

Dont have a scanner.O2 sensor has been replaced,car is a automatic and it does surge with the cruise on also.Will pull a plug to check with hot start issue.
Would a faulty cat exhibit these symtons ?

 

I would suggest you take a look at your Coolant Temperature Sensor as it might be part of the trouble.

If your car starts fine when cold but has a hard time when hot is a good indicator of a bad CTS.
It could be a leaky injector as well but having had one fail on my 1988 C4 Coupe the pressure went to 0 in less than 30 minutes where you saw 30 psi. My injector was leaking for a while as I saw stains below it when I replaced the injector.

If the CTS and MAF check out okay then you should start looking at the fuel system. If your engine was flooded the solution is to hold the gas pedal all the way to the floor to get the ECM to stop adding fuel. Just be sure to let off the gas pedal when it starts running quickly.

If the CTS is telling the ECM it is hotter than it actually is then you would have "cold start" problems as you would not get the extra fuel needed to start the engine.

If the CTS is telling the ECM it is cooler than it really is, the car will use fuel enrichment like a choke. Having a choke turned on all the time makes starting when Hot worse. The long term affect of having the car running too rich is the plugging up of your catalytic converter.

The Corvette computer relies on three important sensors to help get the correct air/fuel ratio the Corvette needs. This is simplified to make it easier to understand as there are a lot more sensors and devices that can affect your ECM.

One is the Oxygen Sensor. You mentioned it has been replaced recently but today that doesn't mean a whole lot. Since you have scanner check the outputs of the O2 to be sure it is indeed working properly.

Another is the Coolant Temperature Sensor. It is critical to have a properly functioning CTS to get the proper a/f ratio during all driving conditions.

The last is the Mass Air Flow meter and it is important as it measures the volume of air being consumed in the combustion chamber. A leak around the MAF between the MAF and the throttle body would cause the Corvette to buck and run erratically. Again with your Scanner find out what your ECM is seeing in real time. A malfunctioning MAF would be able to induce the bucking the Corvette is experiencing. They can be cleaned but you need to be very careful as they wires used in them are very tiny and easy to break. I use the MAF cleaner spray and hose them down and let them dry in the air. The MAF uses tiny wires and makes them get very hot and as the flow of air changes going past the wires they cool down a bit indicating the amount of air going past it. It is a precision device and they do go bad. More often it is a little air getting into the system between the MAF and the throttle body.

When I first read your post I suspected the MAF right away but the having a hard time when hot sounds more like the CTS is bad.

Does your Corvette still have it's Exhaust Gas Recirculation valve working properly? A bad EGR can cause some strange behavior in the Corvette. I have seen Corvettes start having detonation issues and running hotter due to a faulty or disabled EGR valve. To check it connect a hand held vacuum pump to the hose going to the EGR. Using vacuum the diaphragm will move enough for you to be able to see it and the idle speed might change a bit. The EGR is controlled by a Vacuum Solenoid that has a Pulse Width Modulation signal sent to it from the ECM. I had no idea my EGR was bad until I had the emissions tested and it failed due to a higher than normal NOX level.

I hope that you might find something here to help you out with your 1988 C4. If not let us know!

 

thanks for the extensive suggestions for the possible solutions.I do have a CTS,and will check out the MAF also. The running rich could be,as with driving for a 50 mile trips at 50-60 mph the fuel economy seems to be
no greater than 19mpg consistantly.Axle is the 3.07 but I thought cruiseing economy would be more in the low 20s at that average speed.
Thanks to all for the input.

 

Also no codes have been set.

 

Hello again cv1988!

I have the 3.07 rear gears and was able to hit the low 30 mpg's on an interstate with Cruise control and A/C running on my (over 100,000 miles) 1988 C4. You should be able to get into the mid-20 mpg range fairly easily.
The only non stock items on my L98 were the Exhaust and catalytic converters. I had replaced the exhaust with a Chambered Exhaust System and the converter with a Higher Flow unit.

Remove your Oxygen sensor and start the Corvette, watch for pressure coming out the O2 bung. If there is little pressure then your Catalytic converter might be okay still. If there is a lot of exhaust coming out of this hole then it would indicate a plugged or partially plugged Catalytic Converter. I had a Car that was running great when I parked it and 6 weeks later the catalytic converter was "plugged" to a point where my engine would idle but not rev over 1000-1200 rpm. What made it easy to diagnose was back in the day they had a "sniffer cap" where the technician could measure the air/fuel mixture from the engine compartment. Every time I tried to rev the engine the rubber cap would turn into a balloon and upon releasing the gas pedal it would shrink.

What I was referring to earlier was when I bought four new Bosch oxygen sensors from RockAuto I got a bad one. Just because they are "New" doesn't guarantee that they will work. I could not get my money back as they said I installed it and that I might have damaged it. When an O2 fails they tend to make the engine run richer to avoid damaging the engine. This does not mean they all fail that way but most of the ones I have seen where the O2 is bad they tend to go rich versus lean when they fail. I would verify that it is working correctly before assuming it is.

Do you still have the EGR operating on your Corvette? Make sure it is working as that could affect the engine at highway speeds.

Do you have a copy of the 1988 C4 Factory Service manual set? There are two books for this year, one for the Mechanical systems and the second for the Electrical systems. They are priceless when you have any problems with the C4's. I know they are expensive as the last time I bought a set they were just under $100 for the pair of manuals. My daughter has a 2011 Camaro and they wanted over $400 for the set for that car so I bought the entire set of manuals on a DVD for less than $25 on fleabay.

 

Scanner, Fuel Pressure gage, and a set of torx bits are required tools when owning a TPI. You will save yourself a lot of headaches and money if you get a way to read ECM data.

To begin to help , I would want to know what your ECM thinks your CTS and 02s are at as well as your BLMs. Surging could also be caused by the knock sensor pulling timing. Not too common, but it happens. Leaking injectors would also be causing you issues at idle. What about IAC counts? It would be good to see if your IAC is doing anything when the surging is occurring.

Here is another test, go out and lightly peck on your MAF while it is at idle. Also, wiggle the wire harness a bit. Since it occurs when it is moving, it could also be a bad MAF or connection.

 

thanks again Chuck(?) and Kyle-your knowledge of the C4 issues (solutions) is off the charts.
I do have a FP gage and have used it.My overall mechanical skill level is way less than you I'm sure.As far as a scanner which unit would you suggest ?
I am almost certain some or all inj. are leaking after shut off,because by the gage reading goes from 43psi key off,5 min. later 30psi, then 10 psi after 30 min.
As you have suggested there are likely other issues also.

 

Still learning here too. But hey, we all started somewhere.

I use WinALDL and TunerPro RT (both free) on a laptop and a cable from moates.net.

 

MAF cleaned with the proper stuff.After a 50 mile cruise the engine "surge" condition seemed to be gone.Still it was a "not always happening" thing,so will see.
Still plan to replace the CTS sensor for a possible rich running condition also.