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kpickett
07-08-2013, 12:30 AM
I'm having a strange starting problem with my '94 LT-1. If anyone has any suggestions, I'd appreciate them.

It will fire on the first crank, but if I back out of the dock and then kill the engine while the skier gets ready on the platform, it's very difficult to restart. This is before the engine has even warmed up, so I don't think it's a hot start problem. On the other hand, if the engine is hot, it's even more difficult. It will crank and crank and crank, and eventually it will reluctantly cough and turn over. Once it's running, it runs like a top - smooth and powerful.

Here's some information: This has been happening for a couple weeks now.
I changed the fuel filter in the spring. Air filter is clean. Gas is fresh. I ran Seafoam through back in March. I changed the water pump and coolant temp sensor in March. Both thermostats are relatively new, and I checked them in March.

I did the LT-1 cooling fix last year, and the engine stays rock solid at around 170. It does heat soak up a little, but much less than ever before, and as I said, this problem seems to happen even before the engine is up to running temp.

The plug wires are old - at least 7 years, and maybe original. The plugs are only a year old. I pulled plugs, and they look good. There is some corrosion on the coil end of the plug wires. I will replace them.

Could plug wires be causing a restart problem? It doesn't seem intuitive, but I don't know.

Also, the exhaust smells a bit rich. It has always smelled a little rich, but it smells a little gassier than usual. Should I change the temp sensor that feeds the ECM?

Thanks in advance for any suggestions.
Kyle

Jerseydave
07-08-2013, 11:50 AM
My '93 LT-1 has the same problem with hard starting after shut down (cold or hot engine)
Mine also has a hesitation on initial acceleration, does yours do that too?

I've replaced my TPS sensor, but no improvement.

I've heard to check the following but I have not had a chance to do it myself:

-Check fuel pressure when it acts up
-Clean screen at fuel pump inlet

My friend the GM tech says check the fuel pressure regulator, they had many problems with these in the past. I just looked at it, it's mounted on the fuel rail toward the back on the intake manifold. I need to run the boat and then pull the vacuum line off of it and see if any gas comes out. If it does, it's bad. I may just replace it anyway since it's under $50.

The other part that could be a problem is the IAC. (idle air control) Not sure how to test that, but I know some LT-1 owners have replaced them with big improvements.

I don't like just randomly replacing parts so hopefully I can get this figured out.

1redTA
07-08-2013, 12:02 PM
I would check fuel pressure and replace the IAC and plug wires

Jerseydave
07-08-2013, 12:08 PM
I would check fuel pressure and replace the IAC and plug wires

Sounds reasonable. Do you have a picture of an IAC or can you tell me where it is located on my engine? Parts store should be able to get me one I assume, maybe go off the numbers on the old one?

jakethebt
07-08-2013, 12:30 PM
I have an LT-1 and had no idea it had an IACV. I will look tonight. If the LT-1 does, then it could be causing issues. It chokes the air down just like a manual choke. So when it is cold outside, it will restrict a lot of air. When it is hot out side, it will let a lot of air in.

As for location, it will have to be between the air filter and the cold air intake on the engine. They usually have some type of air restriction, either butterfly valve or needle and seat type. They usually have some type of vac or electric control on them. Since this is controlled by a computer, I would look for it to be electric and have a wiring harness.

Just saying... I can not confirm this is your issue, at this time I can only help you with the IACV, if there is one. My LT-1 started a bit hard this past weekend, but I am still on old gas. If it gets worse, I will be watching what you guys are doing.

Jerseydave
07-08-2013, 01:11 PM
This should be the IAC valve for the LT1 engine

http://www.fuelairspark.com/fas/efi-components/efi-sensors/idle-air-control-iac/gm-lt1-style-iac/

Table Rocker
07-08-2013, 01:55 PM
The IAC is located on the bottom of the throttle body. Here is a pic of one from a Z28:
http://www.shbox.com/1/iac3.jpg
http://www.shbox.com/1/iac3.jpg (http://www.shbox.com/1/iac3.jpg)
Also, I believe you have to adjust the IAC position after you change it out so it knows where it is. I found this, but I have no idea if this is how it is done on our boats:
Depress accelerator slightly
Start engine, then release accelerator pedal, run engine for 5 seconds
Turn ignition "OFF" for ten seconds
Restart engine and check for proper idle operation
It is NOT recommended to to push or pull on the pintle of an IAC that has been in service. The force required can damage the threads on the worm drive. Also, do not soak the IAC in any liquid cleaner or solvent, as damage may result. When installing a new IAC, you may move the pintle to match the measurement of the old one. The force required to move a NEW valve will not cause damage to it. Use engine oil to lubricate the o-ring. Tighten attaching screws to 27 lb. in.

http://shbox.com/1/4th_gen_tech2.html
__________________

towelshoot
07-08-2013, 04:36 PM
I picked one up at Advance for $33. It was a BWD part number 21755. I worked perfect. I just installed it and did nothing else.

jakethebt
07-09-2013, 08:03 AM
I picked one up at Advance for $33. It was a BWD part number 21755. I worked perfect. I just installed it and did nothing else.

Why did you change yours? Did it stop the problem?

towelshoot
07-09-2013, 01:35 PM
Mine was having trouble starting the way it should. As someone posted that triggered for me was that it was acting like a carburator engine, not fuel injected. Mine is a 95 and I saw several people with the same engine and close to year that had the same problem. It was an easy and cheap change. It now works perfect. Turn key and it starts again without any gas - the way it is suppose to work.

walterlaughlin
07-10-2013, 04:28 PM
The IAC is located on the bottom of the throttle body. Here is a pic of one from a Z28:
http://www.shbox.com/1/iac3.jpg
http://www.shbox.com/1/iac3.jpg (http://www.shbox.com/1/iac3.jpg)
Also, I believe you have to adjust the IAC position after you change it out so it knows where it is. I found this, but I have no idea if this is how it is done on our boats:
Depress accelerator slightly
Start engine, then release accelerator pedal, run engine for 5 seconds
Turn ignition "OFF" for ten seconds
Restart engine and check for proper idle operation
It is NOT recommended to to push or pull on the pintle of an IAC that has been in service. The force required can damage the threads on the worm drive. Also, do not soak the IAC in any liquid cleaner or solvent, as damage may result. When installing a new IAC, you may move the pintle to match the measurement of the old one. The force required to move a NEW valve will not cause damage to it. Use engine oil to lubricate the o-ring. Tighten attaching screws to 27 lb. in.

http://shbox.com/1/4th_gen_tech2.html
__________________


Hello sir, I just picked up a new IAC for my 95 LT-1 and it did not come with a flat paper gasket as I assumed it would, it only came with a round ring gasket that goes around the base of the pintle. Do I need a flat gasket or am I good to go with the ring gasket? Thanks!

Table Rocker
07-10-2013, 06:05 PM
Hello sir, I just picked up a new IAC for my 95 LT-1 and it did not come with a flat paper gasket as I assumed it would, it only came with a round ring gasket that goes around the base of the pintle. Do I need a flat gasket or am I good to go with the ring gasket? Thanks!
I have never changed mine, so I have no idea. I would guess that the o-ring would do the job and if you needed the paper gasket it would be included, but who knows?

As long as the o-ring seats and seals well, I would probably give it a go. I don't see a source for the paper gasket anyway.

towelshoot
07-10-2013, 07:56 PM
No other gasket needed other than the o-ring seal it comes with. Easy Peasy as long as you don't drop the screw :)

Jerseydave
07-10-2013, 08:41 PM
I read somewhere that you should wipe some motor oil on the o-ring before install. It didn't mention anything about a gasket so I assume there isn't one.

Going to have to try a new IAC on mine next week and see if that cures my hard starting.
For the little cost it's worth it just to have another new part on the 20 year old engine! :D

gotta_ski
07-11-2013, 02:22 PM
The procedure above from Table Rocker is correct. I pulled mine out to clean it last summer and must have moved it a bit in the process. Boat would only start if I pushed the throttle forward in neutral after I put the IAC back in. A day of internet searching to find the above procedure and everything is now back to normal and the boat starts perfect.

JimN
07-11-2013, 02:56 PM
I have an LT-1 and had no idea it had an IACV. I will look tonight. If the LT-1 does, then it could be causing issues. It chokes the air down just like a manual choke. So when it is cold outside, it will restrict a lot of air. When it is hot out side, it will let a lot of air in.

As for location, it will have to be between the air filter and the cold air intake on the engine. They usually have some type of air restriction, either butterfly valve or needle and seat type. They usually have some type of vac or electric control on them. Since this is controlled by a computer, I would look for it to be electric and have a wiring harness.

Just saying... I can not confirm this is your issue, at this time I can only help you with the IACV, if there is one. My LT-1 started a bit hard this past weekend, but I am still on old gas. If it gets worse, I will be watching what you guys are doing.

Most injected engines have a way to maintain idle that's not the throttle plate. They don't have a choke, so the IAC and home setting for the throttle plate act as the choke by closing more when the temperature is low and opening when the temperature is high, as you posted.

The easiest way to find a lot of this stuff is by using Google. In many cases, it will direct you here (assuming you mention marine or Mastercraft).

Jerseydave
07-31-2013, 03:53 AM
kpickett, any updates? Did you fix your hard start problem?

kpickett
07-31-2013, 05:48 PM
Well, it's better, but not quite solved. I tested the fuel pressure at prime, idle, WOT, and for a leak down. It's all perfect. I checked my temp sending unit, and it's fine. I realized there was some corrosion in the plug wires, and I just replaced them yesterday. I replaced the IAC valve, and it's definitely smoother out of idle.

My friend who helped me with the fuel pressure tests thought it sounded like the starter wasn't turning fast enough. You could hear the starter bog down, then spin up to speed, so I took the starter to an electrical shop. They bench tested it and pulled it apart, and it's perfect. BUT, we realized that the brand new battery seemed to be only around 10.5 or 11 volts when it was hot. I'm exchanging it today. I'll let you know what happens. It needed the plug wires and the IAC anyway, and it's running really smoothly now.

JimN
07-31-2013, 07:34 PM
Well, it's better, but not quite solved. I tested the fuel pressure at prime, idle, WOT, and for a leak down. It's all perfect. I checked my temp sending unit, and it's fine. I realized there was some corrosion in the plug wires, and I just replaced them yesterday. I replaced the IAC valve, and it's definitely smoother out of idle.

My friend who helped me with the fuel pressure tests thought it sounded like the starter wasn't turning fast enough. You could hear the starter bog down, then spin up to speed, so I took the starter to an electrical shop. They bench tested it and pulled it apart, and it's perfect. BUT, we realized that the brand new battery seemed to be only around 10.5 or 11 volts when it was hot. I'm exchanging it today. I'll let you know what happens. It needed the plug wires and the IAC anyway, and it's running really smoothly now.

This could easily be a grounding problem. If the alternator hasn't been checked, do that- the 10.5-11VDC tells me that either the voltage is low, the cables aren't conducting well (bad terminals) or maybe the bridge rectifier in the alternator is allowing hte battery to discharge. This can also happen when the battery cables and posts are dirty/corroded, but look fine. Measure the voltage at the battery posts/terminals, then at the cable ends. If you see any difference, address the cause. If you see no difference, move farther down the cables to the next terminal, one cable at a time.

blackcreek
07-31-2013, 09:10 PM
Slow starter speed on my 97 LT-1 was fixed by replacing the terminals on the battery cables. There was corrosion back around an inch or so on all four ends.

kpickett
08-01-2013, 12:24 PM
This could easily be a grounding problem. If the alternator hasn't been checked, do that- the 10.5-11VDC tells me that either the voltage is low, the cables aren't conducting well (bad terminals) or maybe the bridge rectifier in the alternator is allowing hte battery to discharge. This can also happen when the battery cables and posts are dirty/corroded, but look fine. Measure the voltage at the battery posts/terminals, then at the cable ends. If you see any difference, address the cause. If you see no difference, move farther down the cables to the next terminal, one cable at a time.

Thanks, Jim. I will check this weekend. I just exchanged for a brand new battery, too.

wtrskick
08-17-2013, 06:57 PM
I replaced the IAC in my 97 LT1. I also tried the reset procedures but now the engine idles at about 1200 rpm and is running very rich. Anyone have any suggestions.

Thanks

JimN
08-18-2013, 08:39 AM
I replaced the IAC in my 97 LT1. I also tried the reset procedures but now the engine idles at about 1200 rpm and is running very rich. Anyone have any suggestions.

Thanks

What reset procedures? Key ON, WOT three times, key OFF? Running at 1200 RPM indicates that the IAC isn't closing completely but running rich isn't caused by this.

Turn the key on and listen for the IAC to move. DO NOT remove it to do this because the pintle will be pushed out of the end.

wtrskick
08-19-2013, 01:14 PM
What reset procedures? Key ON, WOT three times, key OFF? Running at 1200 RPM indicates that the IAC isn't closing completely but running rich isn't caused by this.

Turn the key on and listen for the IAC to move. DO NOT remove it to do this because the pintle will be pushed out of the end.

Thanks Jim for your reply. The procedures I tried were discussed earlier in this post. I will try this when I get it in the water again.

Thanks again!

Grantw
08-19-2013, 10:33 PM
I just posted a problem I am having which started of somewhat similar to yours, but I was having the problem initially when the engine was hot and it then went to cold starting and now does not start at all. My problem is related to the spark being generated during the ignition cycle and am having a hard time resolving it.

mikeg205
08-19-2013, 10:35 PM
I just posted a problem I am having which started of somewhat similar to yours, but I was having the problem initially when the engine was hot and it then went to cold starting and now does not start at all. My problem is related to the spark being generated during the ignition cycle and am having a hard time resolving it.

Most likely the northstar ingnition module.. IMO

JimN
08-19-2013, 11:13 PM
I just posted a problem I am having which started of somewhat similar to yours, but I was having the problem initially when the engine was hot and it then went to cold starting and now does not start at all. My problem is related to the spark being generated during the ignition cycle and am having a hard time resolving it.

If you have spark, open the throttle a bit and see if it starts. If you have spark during crank and not when you release the key, check out your safety switch and lanyard.

mikeg205
08-19-2013, 11:24 PM
JimN - what is weak spark - low voltage or current to plug? Like there's too much resistance somewhere?

JimN
08-19-2013, 11:43 PM
JimN - what is weak spark - low voltage or current to plug? Like there's too much resistance somewhere?

Has the spark intensity been tested? That's what shops use those big Sun machines for- it shows all cylinders and if one/two (in this case) is low, a coil pack can be moved to a different spot to see if the problem moves with it. If all are weak, it's time to test the wires (if they're old) or look for problems with the crank position sensors (if the signal is weak, the ECM won't recognize it as a "real" crank signal.

mikeg205
08-20-2013, 07:51 AM
Has the spark intensity been tested? That's what shops use those big Sun machines for- it shows all cylinders and if one/two (in this case) is low, a coil pack can be moved to a different spot to see if the problem moves with it. If all are weak, it's time to test the wires (if they're old) or look for problems with the crank position sensors (if the signal is weak, the ECM won't recognize it as a "real" crank signal.

Thanks JimN... you're awesome!

wtrskick
08-29-2013, 01:46 PM
I have replied on this thread before about the issues Iím having with my 97 Prostar with the LT1. I thought I would recap what I have tried. My hard starting issue would occur when the engine was shut off after skiing and getting engine warmed up. We let it idle several minutes at the dock before shutting it off and the temperature wasnít running above normal, (180) on the gauge. If the boat sat for around 15-30 minutes it would start, but act as if was a carbureted engine flooding out. So after reading this thread I tried a new IACV valve and did the procedures to reset it. Now when it starts, it idles at about 1000 to 1200 rpm and runs rich (black smoke out of the exhaust) and the check engine lite is on and will not clear, even after the battery is disconnected for several minutes. I replaced the IACV with the old one and the issues are the same. I tried to find a code reader that would connect to the ecm plug but havenít had any luck finding one that has the right connecting plug. My next move is to take it to a dealer (200 miles away) unless someone has some insight on what I can try.
Thanks

Rossterman
08-29-2013, 03:15 PM
Have you checked temp sensors are working correctly? Overly rich and high idle is typical when this occurs.

JimN
08-29-2013, 07:11 PM
I have replied on this thread before about the issues Iím having with my 97 Prostar with the LT1. I thought I would recap what I have tried. My hard starting issue would occur when the engine was shut off after skiing and getting engine warmed up. We let it idle several minutes at the dock before shutting it off and the temperature wasnít running above normal, (180) on the gauge. If the boat sat for around 15-30 minutes it would start, but act as if was a carbureted engine flooding out. So after reading this thread I tried a new IACV valve and did the procedures to reset it. Now when it starts, it idles at about 1000 to 1200 rpm and runs rich (black smoke out of the exhaust) and the check engine lite is on and will not clear, even after the battery is disconnected for several minutes. I replaced the IACV with the old one and the issues are the same. I tried to find a code reader that would connect to the ecm plug but havenít had any luck finding one that has the right connecting plug. My next move is to take it to a dealer (200 miles away) unless someone has some insight on what I can try.
Thanks

If you have black smoke AND high idle, I can't see a way that it wouldn't throw a code. Do the paper clip code scan (DLC terminals A and B)- plug the paper clip in before turning the key to ON and once the key has been turned, watch for anything other than 1, pause, 2 (designates 12) and see what shows up. If it comes up with 14 and/or 15, the ECT is bad, the terminals are corroded/damaged or the wiring has problems.

Did you replace your TPS? If so, was it specifically an LT-1 part? This is important- if the usual TPS is used, it can be hard to start with the throttle closed and it won't run right because the LT-1 TPS is reversed- the normal one will show WOT when the throttle is closed.

wtrskick
09-04-2013, 08:12 PM
If you have black smoke AND high idle, I can't see a way that it wouldn't throw a code. Do the paper clip code scan (DLC terminals A and B)- plug the paper clip in before turning the key to ON and once the key has been turned, watch for anything other than 1, pause, 2 (designates 12) and see what shows up. If it comes up with 14 and/or 15, the ECT is bad, the terminals are corroded/damaged or the wiring has problems.

Did you replace your TPS? If so, was it specifically an LT-1 part? This is important- if the usual TPS is used, it can be hard to start with the throttle closed and it won't run right because the LT-1 TPS is reversed- the normal one will show WOT when the throttle is closed.

Thank you everyone especially JimN for your input on my problem. I took the TPS out by mistake when I was going to install the IACV and didn't get it back in right. I installed it right and now it idles and runs as it should and no check engine lite. We used it on Monday to ski for about 3 hours and we had no problems with the power or performance. We didn't shut the engine off for more than about 5 minutes because we weren't close to the dock. So we fixed the self inflicted problem, but the original issue probably still exists. The temp sensors have been mentioned as well as possible spark issues. Any suggestions on what steps to take to diagnose it would be appreciated.
Thanks Again for the help.

Jerseydave
09-04-2013, 09:02 PM
Thank you everyone especially JimN for your input on my problem. I took the TPS out by mistake when I was going to install the IACV and didn't get it back in right. I installed it right and now it idles and runs as it should and no check engine lite. We used it on Monday to ski for about 3 hours and we had no problems with the power or performance. We didn't shut the engine off for more than about 5 minutes because we weren't close to the dock. So we fixed the self inflicted problem, but the original issue probably still exists. The temp sensors have been mentioned as well as possible spark issues. Any suggestions on what steps to take to diagnose it would be appreciated.
Thanks Again for the help.

My LT-1 was hard to start also. After replacing the TPS with no improvement, I replaced the ECT and the engine starts fine now. Only ran it one day for about 4 hours but I believe my problem is solved. The ECT is cheap (under $20) and worth a try in your case.