LT-1 hard starting problem

[kpickett]

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]

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]

I would check fuel pressure and replace the IAC and plug wires

[Jerseydave]

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]

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]

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]

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

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]

Fyi

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]

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]

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]

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

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]

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]

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]

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!

[gotta_ski]

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.