This is what happens.....Cold morning, starts up then dies, starts up again then dies. But if I start it and apply a little throttle NO PROBLEM as long as I let it run that way 15-1700 rpm until it warms up to about 160 degrees. BUT once the engine reaches about 135-145 degrees it starts to run rough and the UPSHIFT light blinks on and off as well as the Overdrive icon light. Then after 180 degrees it runs like a champ then and all day long no matter how long it sits.

But in the early morning when it's cold on the next day.....it starts all over again.

I've already replaced the Cold start valve and it made no difference.

Any Ideas?

 

Mine is doing something like that also.

It starts and then immediately dies. I have done a pressure check and according to the FSM it is either the Reg or the pump. I have a new pump ordered and hopefully that will take care of it. I don't mind replacing the pump anyway as it is still the original, so no big deal.



So I would do a fuel pressure check first to rule that in or out. There are several things that may cause this so that should be your first step. Seems I have heard a temp sensor can do what is happening to you as well.

Hopefully there will be some smart folks here in a bit.

Do you have a FSM?

I will also add that when mine first started acting up, it would do that a few times and as long as I kept a little throttle it would eventually smooth out and idle. But it has worsened to the point it won't run at all unless I keep throttle applied.

 

I'll check the fuel pressure.....I have the tools, pressure gauge and -10 so it'll be a easy job.

I also have an extra fuel pump in the shop so I'll be ok if that's it.

Thanks for the help.

I did read the -10 and it stated that could be a cause.

 

haven't heard them referred to a -10 in a while, hopefully you have the -20 or 30 one. Those ten models won't help much on these.

 

Yep......have the -30 and even the FM (LOL)that came with the car.

 

Know of any good places that describe how to check the fuel pressure on an L98? Including how to check for leaky fuel injector?

 

Haynes Repair Manual, TPI models Fuel Pressure 34-39psi Pages 4-2,thru 4-4

1988 Corvette Service Manual, Chart A-7 Fuel System Diagnosis
fuel pressure should be 40.5 - 47 psi and hold steady when pump stops.

 

Ok, it doesn't look too bad. Just run the vehicle dry. Then take the cap off the Schrader valve and connect the pressure gauge. Then start engine and check what pressure you get. Does it matter if the engine is cold or warm when this test is done?

Though, the Haynes didn't say anything about checking for leaking injectors. It did say when you shut the car off, the pressure will drop some. After you shut the car off, how long do you leave the pressure gauge attached to check for leaky injectors or a bad FPR?

The PO put in a new FPR and new Accell injectors. The original spark plugs he had pulled and gave me were carbon fouled. And I noticed a slight miss at high RPM. So, I replaced the spark plugs the PO had put in. And they too were carbon fouled. So, either there is a leak, or it is running rich cause the PO putting in a larger lb. injector. The injectors ohmed okay. But I need to recheck as I believe you are supposed to ohm them when the engine is hot.

I also did read to take the line off the FPR to check for fuel in the line.

Oh, and any tips with regards to the Schrader valve? I had read of someone connecting a gauge to it. Then removed the gauge and started it. And gas started coming out the Schrader valve cause it stuck open. Just didn't want to screw that up. I'm guess you just press the gauge on, and just pull it off?

 

Fuel Pumps aren't intermittent. The Cold Start simply adds a little fuel to get it started. The injectors are then pulsed based on the Coolant Temp Signal and the cooler the temp, the more fuel it gets. You find out what it is by scanning it, but you can buy a replacement sensor and simply plug it into the harness and see what it does cold. If it works, R & R the old one. If not, you'll need to scan it to see what the ECM is seeing and to rule out the ECM (which with the flashing upshift light is a good possibility).

 

UPDATE!

While I had the starter rebuilt, I went and replaced the large fuel filter and cleared the ECM by removing the positive cable for a few minutes.

The car started right up with no trouble.

No flashing UpShift light, no surging idle, the car ran great all day long.

It was 32 outside so I'm sure the trouble is gone and no more starter problems either! It was starting to not engage when the ignition was turned on but after a couple of trys it finally engaged the flywheel.
It was an embrassing event when the car looks perfect but doesn't start right up.....problem solved NOW!

 

Thanks for the update. Many do not give an update when they cure an issue.

The end result is always good to know because many people have the same issues and wait for the fix.

 

I wanted to let everyone know what cured it too.

I thought it was a fuel issue, but didn't try the fuel filter first. I knew I had replaced the fuel pump a while back and never thought the big filter would have been the trouble. I thought it was a cold starting issue because of the cold temps and the gradual trouble of starting up first thing in the morning. As each day went by it became harder to start up and longer to "warm" up.

That lead my train of thought to the cold start injector and I R&R'd it also, which made no difference in starting up the next morning. So my next step was to R&R the Manifold Air Temperature sensor at $11.99 before I moved on to the Mass Air Flow sensor at $149.00. I already R&R'd the ECM last month and knew it would be warranted for a year IF that was the issue.

But after reading the posts here and the Service Manual I decided to try R&R the Fuel filter as a premptive strike while I had the car in the shop on the lift.

If it fixed the problem no harm, and if it didn't...well the Temp sensor was next then the MAF.

But as it turned out the Filter was the culprit and everything is fantastic.

After reading the Manual....it noted that the ECM could not control the amount of fuel if it couldn't deliver that fuel because the filter was plugged up. THAT's why it wouldn't run after it was first cranked up and started, it basically starved itself of fuel. The upshift light blinked on and off because the ECM knew the air/fuel ratio was messed up, so it reads it as lugging the engine.

Anyway............long story short....new filter fixed the problem.

I used to work at the Cheverolet dealership in 1978-87 and was a Service technician for a good while, but it's been 20+ years since I've had to troubleshoot a car and fix it myself, so it's been fun(sort of), but dang happy I don't have to do this to make a living though!

 

I was wondering what year it was b/c the cold-start injector went away.

You might keep an eye on the plugs with those larger injectors. The ECM may not be able to shorten the pulses enough to get the car to run an optimum A/F ratio, causing fouled plugs again but also a plugged CAT, in time. You may be able to adjust by lowering the fuel pressure, which might manifest itself in poorer running due to a lesser spray pattern. Opinions vary on that one.

Not being a fan of the non-Helms manuals, I recommend getting a FSM.

Note: FP is checked with the regulator 's vacuum line disconnected. Any adjustment is to the maximum FP, which is decreased by manifold vacuum. The FSM gives 'bleed-down' times to help diagnose leaky injectors. (I don't have access to mine at the moment.)

 

It's a 1988. It's running superbly now. I haven't had it on a dyno yet or stuck a sniffer in the pipe, but feel it's running very well. The cats I have on it are Flowmaster HighFlow models.

 

I am curious about this,
In my case ( 1986 ) one day it starts and runs fine the next I have to "work" the throttle to keep the idle up for a few minutes then after it gets warm it starts and runs just fine,
So can a bad fuel filter do this? wouldn't a plugged filter act up with the car warm or cold?
Many thanks!
Cheers,
P.

 

That's how mine started. It was intermittent. Then it got to where it wouldn't idle at all. It starts and then instantly dies. As long as I hold throttle it runs fine. I did a pressure check and it only went to about ten and then fell like a rock. According to the FSM, and the trouble shooting charts, it is either the fuel pump or the regulator but my symptoms points to a fuel pump. Probably the check valve. I am still waiting on my fuel pump to arrive after three weeks, from Thunder Racing. I am going to replace the pump the sock and the filter. If this doesn't do it I will replace the regulator. They are both 20 years old so they need replaced anyway.

But in your case I would try the filter first. It couln't hurt to replace it anyway I wouldn't think. But I would do a pressure test as well. That will tell you more where you need to start.

let us know what you find.

When I get mine fixed I will do a write up on it. (if that dang fuel pummp ever gets here)

 

Maybe the fuel filter was wet with water in the tank and when the weather got below freezing the water would freeze until the engine compartment warmed up?