I dont think you really get vapor lock on a line pressurized at 45psi. There's no where for it to boil off to. At key-on, the fuel pump should run for 2 seconds. If there was a lack of pressure, you should hear the sound from the pump as it pressurizes. And as soon as you start cranking, its going to turn the pump on again and circulate more fuel.
On the hot start, does a *small* amount of throttle help or hurt? The *small* matters here, you don't want to trigger a flood clear. If it hurts, the problem is not enough fuel. If it helps, you're getting too much fuel.
1996 Collector Edition Corvette
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TireSmoker
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Re: 1996 Collector Edition Corvette
As pressure rises the regulator is going to let that pressure out.
I had this exact same problem with my Vette in line to get into Dragway 42 last fall. Not certain it's boiling but that is the only time it's been in sitting and multiple hot start situations and the only time I've had a problem starting it since it was put back together.
I had this exact same problem with my Vette in line to get into Dragway 42 last fall. Not certain it's boiling but that is the only time it's been in sitting and multiple hot start situations and the only time I've had a problem starting it since it was put back together.
[quote="Basement Paul"]Is that a mint rocketship on the hood?? :shock:
-BP[/quote]
-BP[/quote]
Re: 1996 Collector Edition Corvette
Well, here's the thing...there is a history related to the hot start issue, but the facts are muddied by other issues going on at the same time (fuel pump problems and changes). Right now things have settled down enough to allow me to concentrate on only these two matters. Consequently, I don't have any very recent hard facts to provide you.
I'm comfortable that the fuel pump situation is good now, and it always pressurizes when I turn the key to the "on" position as noted by watching the fuel pressure gauge. I don't think it's likely that the hot start issue can be caused by lack of fuel when you look at it from a fuel supply perspective. Just to cover all bases, I added some insulation between the fuel lines and the exhaust manifold. Let's see if the issue comes back.
I'm comfortable that the fuel pump situation is good now, and it always pressurizes when I turn the key to the "on" position as noted by watching the fuel pressure gauge. I don't think it's likely that the hot start issue can be caused by lack of fuel when you look at it from a fuel supply perspective. Just to cover all bases, I added some insulation between the fuel lines and the exhaust manifold. Let's see if the issue comes back.
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TireSmoker
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Re: 1996 Collector Edition Corvette
Has any Techron or other injector cleaner been run through the system? Im sure you mentioned, too lazy to scroll back..
Re: 1996 Collector Edition Corvette
Nope. The entire fuel system was cleaned, flushed and new injectors were installed just after I got it. It was job 1. I've changed the fuel filter about 3 times now and cut them open. Very little to see inside.
I went out to do some testing about 1.5 hours ago. Once it got hot (197°), I came home and shut it off and measured the fuel line temp. It was ~150 °. I closed the hood and let it soak. Fifteen minutes later, I checked the fuel line temp again and it was 170°. It exhibited the signs of the heat soak starting issue.
I closed the hood and let it soak again for 45 minutes. Now fuel line temp was 160° and it started instantly. I'm not sure exactly what this proves, but it seems that it might point to some vaporized fuel. Maverick brought up the thought of the alcohol in the fuel vaporizing at a lower temp. I think he has a good point.
I went out to do some testing about 1.5 hours ago. Once it got hot (197°), I came home and shut it off and measured the fuel line temp. It was ~150 °. I closed the hood and let it soak. Fifteen minutes later, I checked the fuel line temp again and it was 170°. It exhibited the signs of the heat soak starting issue.
I closed the hood and let it soak again for 45 minutes. Now fuel line temp was 160° and it started instantly. I'm not sure exactly what this proves, but it seems that it might point to some vaporized fuel. Maverick brought up the thought of the alcohol in the fuel vaporizing at a lower temp. I think he has a good point.
Re: 1996 Collector Edition Corvette
I looked for info on gasohol boiling point vs pressure but didn't find it. When I was fighting fuel vaporization on the Lincoln, I remember finding a statement that some of the blended ingredients of gasohol will boil at 90*F. 
Today, I did find a statement that vapor lock isn't an issue with FI engines with recirculating regulators. Oh? The fuel isn't circulating when the engine isn't running. I'm guessing heat sink is giving Silvia the vapors.
Today, I did find a statement that vapor lock isn't an issue with FI engines with recirculating regulators. Oh? The fuel isn't circulating when the engine isn't running. I'm guessing heat sink is giving Silvia the vapors.Maverick
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Basement Paul
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Re: 1996 Collector Edition Corvette
Sometimes my S10 won't snap off immediately when it's hot under the hood, but if I turn the key to the on position and let it sit like that for about 3-4 seconds before turning it over, it fires right up every time. Maybe it's moving the hot stuff out at that point since the pump is running?
-BP
-BP
Re: 1996 Collector Edition Corvette
You'll need to collect more data to be sure but it looks to me like 170 is too hot. I'd be tempted to wire up an engine coolant temp gauge (or use an old school mechanical) and tape the sending unit to the fuel line there in the danger zone.
[quote="Basement Paul"]Is that a mint rocketship on the hood?? :shock:
-BP[/quote]
-BP[/quote]
Re: 1996 Collector Edition Corvette
ODO: 104412
From recent driving experience in the heat of summer, I've decided to chalk up this "hot start" issue to alky fuel vaporization and move on. I added some insulation to the fuel lines that are exposed to the heat of the exhaust manifold.
I don't know how much it's helping, but I'll revisit the issue if it doesn't resolve itself when the weather cools.
In the mean time, I've addressed a problem with the passenger side door where the window catches on it's upper rear corner preventing the door from opening. The fix was to adjust the door so as to lift the rear edge. The door now opens and closes beautifully with just a click. No rattles. The window felts are as new. In the process of doing this, I had a close look at the door panel and hinges and marveled at their remarkable condition for a car of this age.
So now a previously ignored problem has bubbled to the top of the list...cold rough idle. She starts instantly, almost stalls then struggles to a rough but stable idle. Adding throttle will increase the RPMs, but not clear the situation. It's very difficult to get her moving when cold. She wants to stall and/or hesitate with the application of the foot feed. I'm concerned about the wear on the 27 year old clutch. My first look at it takes me to the Idle Air control (IAC) and the Intake Air Temperature (IAT) sensor. I removed the IAC and it was clean and looked good so I put it back in and performed the reset procedure from the shop manual. I also replaced the IAT yesterday. Neither had an effect on the problem. At this point I'd like to know what the AFR looks like. I think its time to hook up the AFR meter and gather some more info.
From recent driving experience in the heat of summer, I've decided to chalk up this "hot start" issue to alky fuel vaporization and move on. I added some insulation to the fuel lines that are exposed to the heat of the exhaust manifold.
In the mean time, I've addressed a problem with the passenger side door where the window catches on it's upper rear corner preventing the door from opening. The fix was to adjust the door so as to lift the rear edge. The door now opens and closes beautifully with just a click. No rattles. The window felts are as new. In the process of doing this, I had a close look at the door panel and hinges and marveled at their remarkable condition for a car of this age.
So now a previously ignored problem has bubbled to the top of the list...cold rough idle. She starts instantly, almost stalls then struggles to a rough but stable idle. Adding throttle will increase the RPMs, but not clear the situation. It's very difficult to get her moving when cold. She wants to stall and/or hesitate with the application of the foot feed. I'm concerned about the wear on the 27 year old clutch. My first look at it takes me to the Idle Air control (IAC) and the Intake Air Temperature (IAT) sensor. I removed the IAC and it was clean and looked good so I put it back in and performed the reset procedure from the shop manual. I also replaced the IAT yesterday. Neither had an effect on the problem. At this point I'd like to know what the AFR looks like. I think its time to hook up the AFR meter and gather some more info.
Still looking at the rough idle on cold start
I had an opportunity to hook up the AFR meter today, but then I realized that I would have to remove a working O2 sensor to do it. That won't work so that plan was cancelled.
I also fired up my AutoTap app on my laptop. It's a longshot, but AutoTap can read and log info from the OBDII port. So now I have the log and intend to sift through it to see if I can see any anomalies in the data that may lead me to toward a solution. This could be an ECM problem in the cold start table in Open Loop mode. Even if I find it, I won't be able to fix it without outside help.
I also fired up my AutoTap app on my laptop. It's a longshot, but AutoTap can read and log info from the OBDII port. So now I have the log and intend to sift through it to see if I can see any anomalies in the data that may lead me to toward a solution. This could be an ECM problem in the cold start table in Open Loop mode. Even if I find it, I won't be able to fix it without outside help.
Cold start idle fixed
ODO:104565
It appears that the rough idle on a cold start was corrected by increasing the fuel pressure. It's sitting at 52 psi right now. I've also removed the vacuum hose to the fuel pressure regulator and plugged the port on the intake. Watching the fuel pressure on a cold start revealed that the vacuum to the regulator was pulling down the fuel pressure well below the specified 43.5 psi. Without the vacuum hose, I set the running pressure to 52 psi and the engine just loves it. I don't know why it wants this much, but it just plain works.
It appears that the rough idle on a cold start was corrected by increasing the fuel pressure. It's sitting at 52 psi right now. I've also removed the vacuum hose to the fuel pressure regulator and plugged the port on the intake. Watching the fuel pressure on a cold start revealed that the vacuum to the regulator was pulling down the fuel pressure well below the specified 43.5 psi. Without the vacuum hose, I set the running pressure to 52 psi and the engine just loves it. I don't know why it wants this much, but it just plain works.
Clickin', clackin' calipers
ODO: 104724
As the miles pile up in this hot weather, I've tweaked the fuel pressure again to 55 psi. Even at this pressure, with the AC running, if I don't keep the revs up to a level that Silvia will tolerate, she will suddenly cough, or backfire through the intake. As time goes on, I'm learning to manage what may just be the nature of the cam in this car. She behaves much better and is easier to manage without the AC on. Having said all this, I'm enjoying the heck out of tooling around on the NC backroads (but with the top up and AC on).
Today, I found a fix for a bug that has been annoying me since the beginning. Both front brake calipers had a bit of rotational play even though clamped in bracket. That small amount of play produced a click or clack noise when lightly tapping the brakes. I had done YouTube searches in the past with no good hits. Today I found it. GM has produced a fix in the form of spring-like do dads that you insert onto the pads to take the slop out between the caliper and its bracket. Problem fixed. Here's the video: https://youtu.be/O8Jd-zmiKk0
As the miles pile up in this hot weather, I've tweaked the fuel pressure again to 55 psi. Even at this pressure, with the AC running, if I don't keep the revs up to a level that Silvia will tolerate, she will suddenly cough, or backfire through the intake. As time goes on, I'm learning to manage what may just be the nature of the cam in this car. She behaves much better and is easier to manage without the AC on. Having said all this, I'm enjoying the heck out of tooling around on the NC backroads (but with the top up and AC on).
Today, I found a fix for a bug that has been annoying me since the beginning. Both front brake calipers had a bit of rotational play even though clamped in bracket. That small amount of play produced a click or clack noise when lightly tapping the brakes. I had done YouTube searches in the past with no good hits. Today I found it. GM has produced a fix in the form of spring-like do dads that you insert onto the pads to take the slop out between the caliper and its bracket. Problem fixed. Here's the video: https://youtu.be/O8Jd-zmiKk0
Re: 1996 Collector Edition Corvette
ODO: 104745 (August 2nd, 2023 was my second year with Silvia)
Status update of recent activity:
- Last Saturday I had the battery go dead on me after I accidently left the key on for about an hour. Some testing showed that the battery was on it's last leg so I installed a new replacement. Silvia really appreciates all the extra volts.
- I removed the old, unsightly rear deck protector. It's a kind of decal that is applied to the rear deck. The convertible top rests on it to protect the paint from wear. What a bear to get off. Heat gun and labor finally triumphed. I bought a replacement that is simply a die cut soft plastic that attaches employing static cling. It must be removed when driving with the top down or it will blow away.
- After I added the adjustable fuel pressure regulator and FP gauge, the LH injector cover would not fit anymore. My solution was to buy a new replacement cover and cut it to fit over the FP gauge. This was much more difficult than it sounds. After hours of trial and error cutting and fitting I finally got it to settle into place.
In the photo, notice that the embossed "Corvette" logo is not painted in like the original on the RH side. I would hand paint it if I knew how to match the paint. Also notice my permanently temporary fuel line heat protector on the RH side. I'm not sure how much it helps, but theoretically it should.
At this point Silvia is running strong and well and it's great fun to drive fast. I still have to avoid the occasional, surprising bog/backfire, but I'm getting used to that. I just have to keep the revs up before leaning into it.
She starts quickly and settles in to an idle after a few seconds. All good. The AC is still doing great, so I don't hesitate to take her out. My todo list is getting shorter.
Status update of recent activity:
- Last Saturday I had the battery go dead on me after I accidently left the key on for about an hour. Some testing showed that the battery was on it's last leg so I installed a new replacement. Silvia really appreciates all the extra volts.
- I removed the old, unsightly rear deck protector. It's a kind of decal that is applied to the rear deck. The convertible top rests on it to protect the paint from wear. What a bear to get off. Heat gun and labor finally triumphed. I bought a replacement that is simply a die cut soft plastic that attaches employing static cling. It must be removed when driving with the top down or it will blow away.
- After I added the adjustable fuel pressure regulator and FP gauge, the LH injector cover would not fit anymore. My solution was to buy a new replacement cover and cut it to fit over the FP gauge. This was much more difficult than it sounds. After hours of trial and error cutting and fitting I finally got it to settle into place.
At this point Silvia is running strong and well and it's great fun to drive fast. I still have to avoid the occasional, surprising bog/backfire, but I'm getting used to that. I just have to keep the revs up before leaning into it.
She starts quickly and settles in to an idle after a few seconds. All good. The AC is still doing great, so I don't hesitate to take her out. My todo list is getting shorter.
Re: 1996 Collector Edition Corvette
Nice!!! You changed a sick Vette into a great one.
How about this for a protector you don't have to remove?? If necessary, cut some slits to make the bends.
https://fastenation.com/velcro-brand-fa ... 20Products
How about this for a protector you don't have to remove?? If necessary, cut some slits to make the bends.
https://fastenation.com/velcro-brand-fa ... 20Products
Maverick
Re: 1996 Collector Edition Corvette
I've been seeing a spot of oil on the garage floor so I followed the oil trail forward to the Crank Position Sensor under the timing cover. It pushes in and is sealed with an O ring. It's held in place by a single screw. This is a new sensor I installed previously. Back then, I did the installation sight unseen from the top of the engine with my arm extended down to the area in front of the oil pan. It was all done by feel. Here is the result:
Today with a tip from a guy on the Corvette Forum, I put Silvia up on the jackstands and used a bottle jack to lift the engine a couple of inches. Like this, I was able to get my hand into the area of the sensor quite a bit easer to get it out and back in place with a new O ring.