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1988 Corvette hard start hot

 
Old 02-28-2019, 01:45 PM
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desertguyj
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Default 1988 Corvette hard start hot

Busts right off cold start every time. But hot re-start after sits an hour or so, it cranks a long time before starting, like 4 seconds. Either way, the cranking speed is normal.

Last edited by desertguyj; 02-28-2019 at 01:46 PM. Reason: typo
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Old 03-11-2019, 12:40 AM
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85 CRVET
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Mine does almost the same thing as this. Iím no mechanic so Iím not sure but Iíve read about it a lot and Iím thinking that itís the injectors that are leaking causing it to take time to start when the injectors leak when it sits there. When itís cold I think it has evaporated and if I wait a couple days it starts as soon as I turn the key but when I go like to a store or something and shut it off then get back in to start it takes like 5 seconds sometimes to start but it cranks fast like itís not the battery. If I wasnít planning on an intake change next year Iíd change the injectors now but Iíll just wait until I get to change intakes sometime and get new injectors then.
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Old 03-11-2019, 08:55 AM
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Originally Posted by 85 CRVET View Post
Iím thinking that itís the injectors that are leaking causing it to take time to start when the injectors leak when it sits there.
If you think this, next time you try a hot restart, press accelerator pedal to the floor before switch on. This puts the ECM in clear flood mode. If it starts faster this way, you are most likely right.
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Old 03-11-2019, 11:27 AM
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Hook up a fuel pressure gauge at the rail.

Start car cold, notice what it reads and how it holds steady.

Turn car off, watch pressure. If pressure plummets, injectors are probably leaking all that fuel into cylinders causing it to flood.
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Old 03-11-2019, 02:34 PM
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Just be aware that It's not always the fuel pressure that causes Hard starting when the engine is at operating temperatures there are a couple of other things to look at.

Check the output of the Coolant temperature Sensors, on the 1988 there is a single wire temperature sending unit for the gauge on the dashboard mounted between cylinders #1 & #3. The second and more critical one is mounted up in front of the intake system near the throttle body. This sensor has two wires and is the proper sensor that the ECM uses to determine what fuel mixture to use to start the hot car. The two wires are a 5 Vdc Reference Voltage and Signal return. If the 2 wire sensor reads incorrectly it has a huge impact on the Engine and specifically starting issues. It is like trying to engage the choke on while the engine is already at operating temperatures. The Factory Service Manuel has the charts to convert the resistance from the sensors to a specific temperature to get an idea if they are close or way off.

The suggestion of Ray Quayle is a good one to try and I would try it out the next time you try to start the car. Another giveaway is your engine oil and even on the oil on the dipstick will smell like gasoline a lot of times with leaky injectors.

I had a leaky injector but it was just one (Cyl #5) and it was not bad enough to require the floored gas pedal trick to be able to start the car. Leaky injectors can be a big problem, watching how fast the system looses pressure a good indicator that you have a leak of fuel pressure somewhere. I removed the injectors and replaced them at the same time with a fresh set of Bosch Injectors from South Bay Injectors for an awesome price. When I pulled my injectors it was obvious which one had been leaking from the marks and discoloration of the tip. Today the fuel system stays pressurized for a long time and the car starts right away when you turn the key, hot or cold.

I even made sure my cold start system is working properly by replacing the injector and it's sensor that activates it. If you have the cold start system like my 1988 C4 does that too can wreak havoc on your engine if the temperature sending unit or the injector are bad. You can disconnect the wiring harness that attaches to the cold start injector to stop it from contributing. A lot of people like to disconnect your Cold start injector in warmer climates where you don't need the extra fuel to start. I like mine to work in case I need to go someplace with the Corvette in the cooler months.

Good Luck with Your Corvette! You have some serious talent helping you already!
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Old 03-11-2019, 07:04 PM
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Sounds exactly what I was thinking too.
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Old 03-11-2019, 07:08 PM
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I'm going to disconnect that CSI and go from there.
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Old 03-11-2019, 07:22 PM
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Thatís what I am planning on doing because Iíve been reading about that and the next time I drive it I will drive it for a bit then shut it off and try to start it after I put the pedal down.I donít know much but just thought Iíd tell what I thought to help desertguyj get some replies. I also heard of the coolant temp sensor might be bad but I didnít know there was two of them so I will check them if the gas pedal doesnít change the way it starts. I only knew of the one on the cylinder head. I donít have a fuel pressure gauge.

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Old 03-11-2019, 08:38 PM
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cts
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Old 03-11-2019, 09:09 PM
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FWIW, mine starts quicker hot when I floor it hard (clear flood) further indicating fuel leak-down mentioned.


CTS is super cheap and easy to replace, I would do it just for the hell of it. There is always some confusion, endless as to GM CTS's...parts people often confuse them with the temp sensor for the gauge or light on dash. I always say "for the computer." Or bring the old one to parts house.

It would be awesome to be able to get to injectors without pulling that whole plenum???

James
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Old 03-11-2019, 10:58 PM
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[QUOTE=desertguyj;1599029178.It would be awesome to be able to get to injectors without pulling that whole plenum???

James[/QUOTE]
Thats what I was thinking last time I opened the hood while I was thinking about that. Since that all needs done and if I do find out itís the injectors then it wonít be getting fixed until this goes on as long as itís still running ok. I hope to get this around the end of this year.

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Old 03-12-2019, 12:13 AM
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Is this setup considerably better induction wise than stock?

Me I keep everything bone stock, because I was a mechanic for 40 years and had to do a lot of troubleshooting and it was easier when the cars were not changed up much.

While I have that uppers off I am going to replace Fuel press regulator, EGR valve, and egr solenoid as they're buried under there.

In an unrelated topic I obtained an OBD1 scanner OTC4000, and it will not communicate with my ECM. I am thinking possible because someone put a Hypertech Thermomaster PROM chip in it. Looking for a used ECM and stock PROM.
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Old 03-12-2019, 08:31 AM
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A lot of scanners have troubles talking to the older computers, I don't know your scanner but I'd keep trying with it. Sometimes you just have to keep trying until it starts talking.

The FIRST system will be a good bit better than stock, but the runner length is the same, so the torqueyness of the engine will not change and the useable RPM won't really increase a lot, but it will make more power.
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Old 03-12-2019, 11:43 AM
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If it does turn out to be a stuck injector you will want to check your oil for gasoline contamination.
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Old 03-12-2019, 02:51 PM
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I would be careful changing things like the ECM on your car. "If it ain't broke, don't fix it"!! I have a couple old auto scanners and they work great with my 1988 C4. You don't need to spend a lot to get one that works with old Corvettes.

The injectors were done with the manifold on the car and you should not have too much trouble changing the injectors alone.

I removed the whole intake system from my car as I had plugged passageways for the EGR that had to be cleaned out properly for the new EGR to work. The carbon that plugged everything was hard to get rid of, I ended up using a sand blaster to clean it all out. The solenoid for the EGR is located near the thermostat housing and is frequently bad. I learned of my faulty EGR by going through my States Emissions testing station and my NoX was way too high which points to the EGR. Mine was totally dead so I replaced all the parts and made it work properly again. Cleaning the passageways for the EGR is important. The carbon is hard and tough to get out easily so you will need some brushes like the ones used to clean oil passageways in the block before building the engine. I used a hard ice pick and a small sandblaster to clear all the carbon out. I am a big believer in keeping the car working properly within the emissions laws.

Order a set of injectors a week before you need them, My set was about $170 for eight Bosch Injectors for the Corvette. Removing the manifold is a P.I.A. so after taking mine off I sand blasted all the parts inside and out then painted them silver again.

If you plan on keeping the Corvette it is imperative that you purchase a Fuel pressure Gauge and the Factory Service Manuals (either in hard copy or DVD) so you have them. The gauge is not that expensive and you will use it a lot with C4 Corvettes and other fuel injected cars.

Before you start work on removing parts from your manifold use lots of a good penetrating oil and soak the hardware with it. I like Kroil Oil as it really gets into tight spaces. Those bolts have been there a while so keep a hot air gun or torch around to heat up the hardware that appears stuck. I ended up heating hardware and then soaking it with Kroil Oil just to help loosen things up a bit. You do not want to break any of the bolts you are removing. I coated my hardware with anti-seize to make it easier if I have to go back in there.

Keep us posted on what you learn, you have a bunch of us wondering what is wrong with your Corvette! We will get it figured out!!

Best Regards,
Chris

One more thing: Replace ALL of the vacuum tubing that you can see and find while working on your Corvette, it will save you trouble down the road.
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Old 03-13-2019, 08:15 AM
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I tried the gas pedal down and Iím pretty sure it does start faster that way. But then I shut it off to retry it a few times and I think I realltbflooded it clicking the gas pedal too much haha. Because it took longer to start than it ever does after I tried a few times. Iím thinking I will just wait until I get that intake and then I will put new sensors and injectors on that intake. I should get a fuel pressure gauge sometime to make sure though. Are you changing yours soon dessrtguyj or do you want a better intake now too?

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Old 03-15-2019, 12:52 AM
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It is an OTC Monitor 4000 with the TPI harness. Wish I knew why it will not communicate. It does work. I tested it on another old OBD1 GM car.

Also mine fails for HC if I don't kick the timing back to about zero temporarily. It cleans it up remarkably to almost undetectable levels at hi speed and idle!
Then after pass I put it at 6 degrees. Just an fyi.
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Old 03-15-2019, 12:55 AM
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Hope that fixes it, the injectors that is.

No I will keep stock intake, I dont like to deviate fron stock. And just an FYI, I have "re-Bosed" many Corvettes. That system sounds awesome.
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Old 03-15-2019, 12:56 AM
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Going to replace the injectors and anything under the plenum soon as I can.
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Old Yesterday, 01:11 PM
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I have been keeping eye on possible oil pollution by gas. Seems to be clean and no gassy smell. I did change it and it remains pure, fwiw.
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