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Old 07-20-2008, 02:30 AM   #1
Photomania
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Default Hard to start but runs fine when it finally starts

I drive a 1990 six-speed coupe with a L98 engine. Over the past two weeks, the engine is getting hard and harder to start. Once it cranks up, I can turn it off and it cranks back up fine. Occasionally, it's hard to start when it sits for 20 or 30 minutes (when I go in a fast-food restaurant and eat). It sounds like it's struggling to start and sounds almost as if it won't start and then it finally starts.

On Friday, I replaced all of the spark plugs and spark plug wires. I was going to do that anyway because the plug wires appeared to be the original ones. I bought the car when it had 78,000 miles and now it has 112,000 miles.

I also cleaned the air filter and sprayed throttle bottle cleaner inside the throttle body. I removed the distributor cap and cleaned all of the contacts, which had some light powder on them. One of the spark plug wires had some light powder inside the boot.

The "Service Engine Soon" light has not come on during all of this.

I put a new fuel pump in the car about 25,000 miles ago, as well as a new fuel filter. At that time, I also replaced the ignition coil, distributor cap, rotor and ignition module. I replaced the alternator back in April, and it's charging well.

It seems like this must have a simple solution since the engine runs fine once it starts. It doesn't stall or try to cut off. The fans don't come on until it gets hot. What should I do next?
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Old 07-20-2008, 02:34 AM   #2
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Do an ohm test hot, and cold, on your injectors. Mr. FIC will chime in I imagine and tell you what else to look at w.r.t. injectors. Search C4 threads; you can find proper ohm specs...
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Old 07-20-2008, 03:44 AM   #3
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Check the fuel pump relay. It sounds as if the relay has failed, and the fuel pump is having to be energized by the backup circuit, which is the oil pressure switch. In this event, the engine has to build oil pressure to close the switch.

If the relay is working correctly, the oil pressure switch never enters the equation.

Check fuel pressure at the schrader valve during one of these hard start events. I'm betting it's zero until the oil pressure switch closes.
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Old 07-20-2008, 09:06 AM   #4
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Quote:
Originally Posted by Photomania View Post
I drive a 1990 six-speed coupe with a L98 engine. Over the past two weeks, the engine is getting hard and harder to start. Once it cranks up, I can turn it off and it cranks back up fine. Occasionally, it's hard to start when it sits for 20 or 30 minutes (when I go in a fast-food restaurant and eat). It sounds like it's struggling to start and sounds almost as if it won't start and then it finally starts.

On Friday, I replaced all of the spark plugs and spark plug wires. I was going to do that anyway because the plug wires appeared to be the original ones. I bought the car when it had 78,000 miles and now it has 112,000 miles.

I also cleaned the air filter and sprayed throttle bottle cleaner inside the throttle body. I removed the distributor cap and cleaned all of the contacts, which had some light powder on them. One of the spark plug wires had some light powder inside the boot.

The "Service Engine Soon" light has not come on during all of this.

I put a new fuel pump in the car about 25,000 miles ago, as well as a new fuel filter. At that time, I also replaced the ignition coil, distributor cap, rotor and ignition module. I replaced the alternator back in April, and it's charging well.

It seems like this must have a simple solution since the engine runs fine once it starts. It doesn't stall or try to cut off. The fans don't come on until it gets hot. What should I do next?
when it does finally start does it have excessive smoke and smell of fuel.? Can you check fuel pressure running and after shutdown. ALso do an ohm check on the injectors cold then hot . Report results
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Old 07-20-2008, 09:55 AM   #5
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I'm hoping I read your post wrong, but have you not changed the fuel filter in 25,000 miles?
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Old 07-20-2008, 04:05 PM   #6
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My 96 LT4 is doing the same thing for the past month. No smoke when it does start, and restarts just fine. service engine light is on. I'll be interested in your results. I really need to change the spark plug wires on the drivers side. Anyone have any tips on how to get to them on the distributor? I can see the pass side ones easily, but the drivers side ones, I can't get a look at, even on the lift. thx
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Old 07-20-2008, 06:25 PM   #7
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Quote:
Originally Posted by Frizlefrak View Post
Check the fuel pump relay. It sounds as if the relay has failed, and the fuel pump is having to be energized by the backup circuit, which is the oil pressure switch. In this event, the engine has to build oil pressure to close the switch.

If the relay is working correctly, the oil pressure switch never enters the equation.

Check fuel pressure at the schrader valve during one of these hard start events. I'm betting it's zero until the oil pressure switch closes.
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Old 07-20-2008, 06:29 PM   #8
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Originally Posted by bgrant_12002 View Post
Anyone have any tips on how to get to them on the distributor?
I posted up on this on the other thread for wires...
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Old 07-20-2008, 07:23 PM   #9
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Does fuel pump run when you turn the key on before you start it? If it does, it isn't the fuel pump relay, if not, it's probably the relay. It could be losing pressure through the pressure regulator or the check valve in the fuel pump, but you just changed it, so that's probably not it.
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Old 07-20-2008, 09:39 PM   #10
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Quote:
Originally Posted by bgrant_12002 View Post
My 96 LT4 is doing the same thing for the past month. No smoke when it does start, and restarts just fine. service engine light is on. I'll be interested in your results. I really need to change the spark plug wires on the drivers side. Anyone have any tips on how to get to them on the distributor? I can see the pass side ones easily, but the drivers side ones, I can't get a look at, even on the lift. thx
Update............I took a look at the spk plug wires on the drivers side closely and then started it..........two wires were touching each other and one touching a piece of metal, grounding it out.........went to parts store and got some extra looms............missing problem solved, but still hard to start when cold.

Last edited by bgrant_12002; 08-10-2008 at 10:44 AM. Reason: error
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Old 07-24-2008, 11:33 PM   #11
Photomania
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Default Been out of town

Sorry for the delay in getting back. (Was on an 800 mile trip and didn't have access to a computer.)

Yes, I can hear the fuel pump energizing when I turn the key. I have a fuel pressure gauge and I'll check the pressure. As for smoke in the exhaust, I didn't notice any smoke. Nothing smells unusual.

I haven't changed the fuel filter in about 25,000 or more miles. Is it time to change that already?
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Old 07-26-2008, 12:50 AM   #12
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Under normal circumstances the fuel pump filter wouldn't need changing at 25000 miles, but cars that sit for long periods get moisture condensation in the fuel tank and debris. Its easy and cheap to change though and one potential problem out of the way. If the filter is causing a hard start it would also cause poor running which you don't have. The fuel pressure readings may point to your problem. The fuel pressure regulator is also suspect, you should have about 40 psi fuel pressure.
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Old 07-26-2008, 10:47 AM   #13
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I would also say fuel pump.

I had a pump changed in a car and after 3 weeks it died.
here was my problem.

there is a check valve in the pump that keeps the system primed after the car is shut down.
if it sits for a 30+ minute period, the fuel would run back into the tank and out of the system.
the pump then had to "re prime" the system every time you started it after sitting, but would run perfect afterwards.
this actually happened on 2 of my vehicles. a turbo dodge and my S10,
both of which use the same walboro pump as the vette.
and they both had the same problem of hard to start after sitting, both of which had bad pumps.
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Old 08-30-2008, 07:49 PM   #14
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Default Hard Start 92' LT1

Hello all,
OK, my vette is acting up and I can't figure out why she is so temperamental!

I was driving to work and the car just lost all power on the road. She didn't stall but couldn't even get me up a small hill. Parked it. waited a half hour and managed to get it to the ASE Mechanic I trust. From that point we replaced the plugs, checked all wires, changed both O2 sensors, fuel pump and strainer (we didn't need to replace the wiring harness though) We also changed the fuel filter. While waiting for some of those parts we ran the injectors through the sonic cleaner about 6 times, and replaced the little injector seals. Two of the injectors are a little weak. So we marked them and put them up front for easy replacement, pocketbook permitting. Once that was all finished I started it up. Hard Start! I let it go for a few days to see if it would go away but never did.

Came back to the shop where we spent about 8 hrs diagnosing. Using the fuel pressure gauge, he checked the pressure with key on and engine off, engine running, engine after turning off, etc.. We hooked up the diag machine, no code. All fuel pressures are good, like 40-45 psi. Fuel pump activates when key is turned on before starting. We fixed a small vacum leak. He checked the Fuel pressure regulator and said that's not it. No smoke but there is a fuel smell that came into the cockpit and was evident by the engine as well. after starting which ceases after about 20 sec or so. We re-tightened the fuel filter because it WAS leaking and the fuel smell stopped, but the Hard start continued. We checked the rest of the fuel system for leaks. None. In the last few days the fuel smell has returned. I'll go back to check on the fuel filter this week. Another thing the SYS warning light flashes every so often.

When I try to start the car. I even turn the ignition to the on position and wait for 15 seconds then start and still cranks but doesn't start unless I keep cranking. giving some gas while cranking seems to be helpful if not necessary. Usually it will start on the 2nd or 3rd 2-5 second cranking session. After it's been running for awhile and I turn it off I can start it right back up, but if I go into the Pizzeria of Cafe', I gotta crank on it again for 3-5 seconds before she'll start up again.

Please HELP a War Vet with his Corvette!!
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Old 08-30-2008, 09:06 PM   #15
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Quote:
Originally Posted by WaverunnerRC View Post
Hello all,
OK, my vette is acting up and I can't figure out why she is so temperamental!

Please HELP a War Vet with his Corvette!!
Woh.....major thread Hijack here... Although you have similar symptoms as the OP, you need to start your own thread or the waters get too murky.

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Old 08-30-2008, 09:19 PM   #16
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Quote:
Originally Posted by Photomania View Post
Sorry for the delay in getting back. (Was on an 800 mile trip and didn't have access to a computer.)

Yes, I can hear the fuel pump energizing when I turn the key. I have a fuel pressure gauge and I'll check the pressure. As for smoke in the exhaust, I didn't notice any smoke. Nothing smells unusual.

I haven't changed the fuel filter in about 25,000 or more miles. Is it time to change that already?
If you rule out your fuel pump and FPR, the next thing that comes to my mind is leaky injectors. At 112K miles, do you know if your injectors are original ? If you still have the original multecs, they may be nearing end of life. I would pop off the fuel rail, and check both the spray pattern and wether any of then leak when engine is turned off(need glass jars to catch the fuel all 8 injecters).
Perhaps an easier and less labor intensive way would be to check how long your fuel pressure stays at ~40psi when you shut the engine off. The pressure should diminish very slowly.

just my $0.02

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Old 08-31-2008, 02:53 PM   #17
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Been there done that. I'm at about 109K, with original injectors, and no injectors are not leaking I ran them extensively through the Sonic Cleaner testing through full spectrum of flow rates, including, leak tests, after each cleaning x6. But I do have 2 with slightly decreased flow as I stated in the original Post, about 10% less then the others. The pressure remains around 40psi at 30 minutes after engine is off.
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Old 08-31-2008, 02:53 PM
 
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