GT40 intermittent idle problem

[boo]

I spoke with Hickok and they said models 007-0041 and 007-0041A will work on my GT-40 engine. On March 1, I will be extracting any fault codes, if they exist, from my engine's computer. Stay tuned.

[jjgag60]

Star tester

I purchased a star tester and it works great. When hooked up, it actually runs the motor through a self test. Make sure you position the cord out of the way of the pulley for the water pump, several of the star testers have had the cord get caught in the fan belt and ruined the tester. You need to read the instructions in the Gt-40 manual on how to set it up. Remember when you do replace any sensors you should remove the negative post on the battery and let it set for while so the computer shuts down. If you dont the computer will think the old problem exist until after several start and shut down cycles. I found the temperature sensor was my problem when it wouldn't idle

[boo]

Dear jjgag60,

I'm the original poster of this thread and I greatly appreciated reading your reply. If you don't mind, I would like to ask you some specific questions.

Did you have the idle problem every time you started your boat cold like I do?

Using the Star Tester, did you receive a code for the ECT (engine control thermostat) failure?

If you did, was it during the KOEO (key on engine off) or the KOER (key on engine running) mode?

What was the code number?

How many times have you used your boat since the ECT was replaced?

Sincerely,
Tom T. (Boo)

[boo]

Today, we ran the tests on my engine. The symptom appeared as usual when we started the engine. We brought the engine up to operating temperature. The KOEO (key on engine off) test resulted in an “11” code - PASS. The KOER (key on engine running) resulted in the engine automatically going through several cycles of higher and lower rpm’s as it was supposed to. Unfortunately or fortunately, depending on my point-of view an “11” code - PASS was the result.

What this means is the ECT, ACT, MAP sensor, water temp sensor, oil pressure switch, knock sensor, PIP, and throttle position sensor is/are functioning properly. Hang in there everyone. I will get this symptom fixed and everyone hitting this thread will benefit. With so many hits on this issue, it must be quite common for this GT-40.

Next, we plan on doing the Pinpoint Tests as outlined in the manual. Step-by-step as directed, we’ll be testing vacuums, fuel system, etc.

As a sidebar to all this, the GT-40 manual states that my GT-40 engine has Failure Mode Effects Management (FMEM). Should the ECT, ACT, and TP fail to send out an input, the computer (ECA - electronic control assembly) would go into the FMEM mode and increase the engine idle rpm’s to 800 instead of its normal 600 rpm idle. This has nothing to do with my problem, simply passing on information from the manual.

Stay tuned. I will fix this cold start idle problem.

[Lewy2001]

Boo the idle speed control solenoid bypass (ISC-BPA) could be your problem. It controls the amount of air that gets past the throttle body butterfly valve at idle and on deceleration when the butterfly is closed. I have been trouble shooting a different problem on my GT40 engine and also found the KOEO, Continuous test and KOER returned no fault codes. The manual states that the ECA does NOT store fault codes for the ISC-BPA. Have cleaned the solenoid and the inlet manifold passages with carby cleaner. There is a wire mesh filter like material which the manual calls a muffler in the passage behind the butterfly mine was quite dirty. Give the cleaning a try and see how that goes before replacing the solenoid.

I purchased the Equus 3145 Ford Digital Code Reader mentioned earlier is this thread from Amazon for $24.15 it comes with a very good manual which explains how the EECiV computer works and a more detailed fault code list.

You cold start problem could be that the solenoid is sticking when cold and not allowing enough air into the engine. On first start the GT40 engine idles fast around 1000-1200rpm and then settles down to 650-700rpm after a short time. If yours does not idle fast when first started I would almost bet the Idle speed solenoid bypass is your problem.

[boo]

Lewy 2001,

Thank you. I keep the screen very clean and have removed and visually inspected the ISC-BPA also known as the IAC (intake air control). When I start the engine is does idle up to 1000 - 1200 rpm's for about 3 seconds and then it drops and starts the up and down searching to the point of almost stalling.

The reason I think the IAC is okay is because the manual stated I would have a stall problem upon rapid deceleration if the IAC was bad. I do not have that problem.

Our next test session with the mechanic is set for next week.

[boo]

Yesterday, I connected a fuel pressure gauge to the valve on the fuel rail. Started the engine on the wash rack. This was after a morning of skiing and the engine has cooled down during the twenty minute ride from the water to the wash ramp. We ski in salt water. The engine idled perfectly. This has never happened in the last six months. It always has the loping idle and then it would eventually stall.

Today, I launched the boat with the fuel pressure gauge connected to the fuel rail valve. Started the boat and it idled perfectly. This has never happened in the last six months, either. The fuel pressure at idle was 34.5 psi. The manual specification is 31 psi plus or minus 3 at idle. Unfortunately, I was not able to check the fuel pressure with the symptom present.

After skiing for 3 hours today, I trailered the boat to the wash ramp. Started the boat to flush the engine and the loping idle was present. Conclusion, connecting the gauge removed the symptom and the engine idled perfectly both times the gauge was installed. Why? I don’t know yet. Was there air in the system that the gauge’s hose bled out? Not sure but I will go back to the manual’s Pinpoint Test section and proceed with more tests.

Keep in mind that the engine runs perfectly except for the first start upon launching the boat and after it has sat for about 30 minutes. Stay tuned. I will fix this problem.

Tom T.

[boo]

The boat sat yesterday afternoon and all day today. After work today, I drove to the boat and connected the garden hose to the engine’s flush connection. Instead of connecting the fuel pressure gauge to the relief valve on the fuel rail, I did something different. I unscrewed the relief valve’s cover and used a small flat tip screwdriver to depress the valve’s stem - just like you would release air from a tire if you overinflated it.

I placed my ear very close to the valve as I depressed it very, very gently with the screwdriver hoping I might hear some air flow out of it. I did not hear any air. I removed the screwdriver from the valve tip so it would spring back closed and then threaded the cover over the relief valve.

Next, I started the engine. It idled up perfectly for about 5 – 6 seconds and came down to its proper idle speed. In other words, the engine idle loping did not occur. I’m definitely onto something. The engine never should have idled properly after putting it away yesterday when it loped on the wash ramp. Every time I’ve depressed that valve stem, the next time I start the engine it idles perfectly.

For now, this will be my last post until I figure out why pressing the relief valve on the fuel rail causes the engine to idle correctly on a cold start. The cause is probably a vacuum leak. I will find it if that’s the culprit.

I’m not a mechanic so what I’m about to say please consider the source. I do not know how long it takes for the fuel rail pressure to subside, so pressing the relief valve, I would assume, could produce catastrophic consequences if its still under pressure. Something like an explosion or fire.

With 900 views to this thread, I hope I’ve helped some of you with my postings. So far, I’m very happy with the results. My next post may take weeks or months but I will post the final outcome.

If any of you have been able to temporarily resolve your idle issue using this method, please post it here. I would like to know.

Tom T.

[gtxragtop]

The boat sat yesterday afternoon and all day today. After work today, I drove to the boat and connected the garden hose to the engine’s flush connection. Instead of connecting the fuel pressure gauge to the relief valve on the fuel rail, I did something different. I unscrewed the relief valve’s cover and used a small flat tip screwdriver to depress the valve’s stem - just like you would release air from a tire if you overinflated it.

I placed my ear very close to the valve as I depressed it very, very gently with the screwdriver hoping I might hear some air flow out of it. I did not hear any air. I removed the screwdriver from the valve tip so it would spring back closed and then threaded the cover over the relief valve.

Next, I started the engine. It idled up perfectly for about 5 – 6 seconds and came down to its proper idle speed. In other words, the engine idle loping did not occur. I’m definitely onto something. The engine never should have idled properly after putting it away yesterday when it loped on the wash ramp. Every time I’ve depressed that valve stem, the next time I start the engine it idles perfectly.

For now, this will be my last post until I figure out why pressing the relief valve on the fuel rail causes the engine to idle correctly on a cold start. The cause is probably a vacuum leak. I will find it if that’s the culprit.

I’m not a mechanic so what I’m about to say please consider the source. I do not know how long it takes for the fuel rail pressure to subside, so pressing the relief valve, I would assume, could produce catastrophic consequences if its still under pressure. Something like an explosion or fire.

With 900 views to this thread, I hope I’ve helped some of you with my postings. So far, I’m very happy with the results. My next post may take weeks or months but I will post the final outcome.

If any of you have been able to temporarily resolve your idle issue using this method, please post it here. I would like to know.

Tom T.

The fuel rail should contain pressurized fuel if it is like an automobile engine. So when you push the relief valve, a fair amount of gasoline should come squirting out.
NEVER air. If nothing comes out then I do not see what difference this would make it starting it later. Nothing came out when you depressed the valve so in theory
nothing changed.

[boo]

Boo here again. I've been keeping a spreadsheet of my engine start idles. Nothing conclusive yet. This is my first attempt at including an attachment. I've read the site's instructions on how to attach but this may not work do to operator error.

[boo]

My most recent start information is attached. Still nothing to report on what's causing the loping at idle.

[boo]

Boo here again,

PCM asked for a compression check. We did the test in between sets so the engine was hot.

#1 - 147
#2 - 157
#3 - 155
#4 - 163
#5 - 160
#6 - 160
#7 - 155
#8 - 160

Then the dealer recommended checking the intake manifold bolts. The upper intake manifold bolts were tight. Two bolts of the lower intake manifold were slightly loose. I turned them about 1-2 degrees. The next day's morning start showed no improvement. It was a loping idle. Still no fix yet.

[boo]

September now. No idle problems all summer. Our summers are mild. September is our warmest month. First start of the morning is fine but sitting at the dock on a warm morning for about 15 - 20 minutes the loping idle returned. Will wait until the winter months when the first start of the morning creates a loping idle consistently and will probably replace the IAC as Gordon did on his boat.

[boo]

Replaced the AIC (purchased from the dealer) and the loping problem still exists.

[Chexi]

Is you ignition timing set correctly? I ask because I had 2 problems with my GT40 when I bought it used. First, the RPMs would bounce around and go crazy, I would get a ticking sound like a short, and ultimately the engine would die. This was usually when warm. This required a new distributor, or at least the sensor inside it. The second issue was a loping idle. This was fixed with the timing of the distributor.

If you have perfect pass, perfect pass can also cause a loping idle. I believe it can be caused by the servo being mounted incorrectly. I think the manual has a troubleshooting item on this point. I don't think this is it, but worth looking into if you have perfect pass.