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GT40 won’t idle |
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skeet 
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Joined: June-15-2020 Location: NE Alabama Status: Offline Points: 17 |
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 Topic: GT40 won’t idlePosted: June-12-2022 at 2:28pm |
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1998 SN GT40
Will turn over and catch immediately but dies within 4 sec. New plugs, wires, cap, rotor last year and would run well. Sometimes a hard start when hot. This led me to new injectors this past winter. New intake gasket. Injectors are 24lb blue top Mustang. Also installed perfect pass over the winter. Put it in the water. Cranked up. Idled rough. Got it out on the water. Ran well. Got back to boat house, idled rough and died. Will run if give it some feathered throttle. Not smooth and will backfire. Seems like a too lean condition to me. Fuel pressure steady at 40. Checked gasket for leaks under intake. Disconnected PP linkage and no joy. TPS and IACV are getting power. I’ve been through the Poor Man thread and the PCM handbook. But I’m not the best modern engine mechanic. Any help would be great! Thanks! |
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cbr1000dude
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Joined: August-23-2011 Status: Offline Points: 330 |
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Posted: June-12-2022 at 4:52pm |
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Well, you have fuel, compression (ran well), that leaves spark and timing. I'm no expert, but that's all it takes to run and idle. So, what kind of distributor do you have? I just replaced mine so that's where I'd start since you have "hot no start" like I had. Sorry, just a guess.
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skeet
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Posted: June-12-2022 at 5:00pm |
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Distributor is a good guess since it’s running rough and wants to backfire like it’s out of time. I’ve checked the wires. They’re in the correct order. New cap and rotor. No moisture. No play in the rotor movement.
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KENO
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Posted: June-13-2022 at 6:06am |
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I'd read the link below to an old thread and remove the IAC valve ( also called the Idle Speed Control Bypass Air Solenoid ) and see if it idles with it out. Don't just unplug it, remove it. The solenoid may be dead and not opening It provides a path for air flow around the throttle butterfly valve when the engine is idling and if it doesn't open when it should, the engine won't idle. It may not be the problem, but it's free and easy troubleshooting without throwing parts and money at it just yet.  . |
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skeet
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Posted: June-13-2022 at 7:06am |
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The IAC is getting power but not activating. It won’t idle with it out,
unfortunately. I’m replacing it today anyway. I’ll see if a functioning one helps. Thanks! |
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dshack
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Posted: June-13-2022 at 12:02pm |
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I'd 2nd the suggestion of the distributor (not just the cap). On my 01 SAN w/ GT40 I had a similar "intermittent" rough idle. I (eventually) pulled the distributor and the PIP was falling apart. I replaced the distributor and it ran perfect immediately.
If you haven't already, it's also worth backprobing the TPS and checking voltage to see if it is a nice smooth voltage curve from about .9V to 4.5V as you increase throttle. Quick and easy way to confirm your ECU isn't getting bad data on throttle position.
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skeet
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Posted: June-13-2022 at 12:22pm |
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Good suggestions. Will do.
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KENO
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Posted: June-13-2022 at 1:20pm |
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Since you've been through the Poor man thread, you probably have a distributor number that works I'd imagine, if you decide to head off in that direction.
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gun-driver
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Posted: June-13-2022 at 1:41pm |
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My money would be on the bad distributor.
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skeet
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Posted: June-13-2022 at 4:06pm |
I'm looking at Duralast Gold Distributor BDLG-FD14 with cast iron gear |
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KENO
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Posted: June-13-2022 at 8:19pm |
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That works, has the right gear
The vent hole on the cap needs a glob of silicone so that it's not a vent hole anymore. Or if your recent new cap has the glob already, use that one and you'll have a spare Another choice would be Spectra FD-14 You'll find a wide range of prices.
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skeet
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Posted: June-13-2022 at 9:19pm |
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Good info!
New IAC was not the solution. It cranks and fires but idles way too low and then dies. |
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skeet
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Posted: June-14-2022 at 1:45pm |
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https://www.ebay.com/itm/224516127749
Here is a link to the injectors I installed. Anyone see a fault with those? I can't help but suspect them since I didn't have an idle problem before... I may put the old ones back on to rule out the new ones.
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dshack
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Posted: June-14-2022 at 2:51pm |
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Those look correct to me. One of the (many) issues that I inherited from the prior owner of my GT40 was injectors with too high of a flow rate. They were causing flooding and running rich. What tipped me off was that I occasionally needed to start the engine at WOT (out of gear of course). Doing this triggers the injectors to not run momentarily to clear a flooded engine.
Does cranking it up at WOT seem to help? Alternatively, it's entirely possible one of those new injectors is defective. If that's the only thing you changed I would definitely try swapping back just to eliminate that possibility as you said. |
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KENO
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Posted: June-14-2022 at 3:38pm |
Somebody might suspect that there was human error involved and maybe you messed up an O ring or 2 when installing the new injectors. Somebody has to stick up for the injectors What gasket(s) did you change? Back in post #1 you mention having a constant 40 psi, while the engine is running presumably. It should be down around 31psi plus or minus 3 when it's idling with normal vacuum and 39 psi plus or minus 3 at full throttle or with the Key on Engine off. and somewhere in between the 39 and 31 numbers at part throttle depending on engine load which directly affects vacuum The vacuum is sensed by the regulator and it controls fuel pressure based on that. Have you checked the vacuum while it's idling ? It should be around 15 in Hg. and pretty steady or if it won't stay running unless you give it some throttle what's the vacuum at that time? |
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skeet
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Posted: June-14-2022 at 4:04pm |
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Excellent questions!
I'm presuming the o-rings are good since they aren't leaking any fuel at the rail or head (after one was and it was due to me tearing it on seating). I changed the intake gasket. I took the intake back off to check and the gasket looks good. When I hook the pressure gauge to the fuel rail, it takes about half a dozen key turns to get the pressure reading to 40psi. Then it does not fluctuate afterwards. This had me curious as well. I thought it might should drop as it's trying to idle but it does not. I have not checked vacuum when it's trying to idle because I didn't know what is normal. Now that I know 15 is what I need, I can T into one of the tubes coming off the underside of the manifold and see what I have. If the vacuum is low, that would explain the higher fuel pressure and no idle. I'm guessing there aren't many places for a vacuum leak if I've ruled out the intake gasket. On a car, I would spray carb cleaner around the manifold to find a vacuum leak but not sure about this particular engine.
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skeet
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Posted: June-14-2022 at 9:46pm |
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Hooked up vacuum gauge and fuel pressure gauge.
Vac was around 15 and fuel pressure was around 40 while it was trying to idle. Pulled vacuum on the fuel pressure regulator and it held. Checked the old TPS and it’s voltage was correct. Pulled the new fuel injectors and put the old, original Ford injectors back in. Fired up and ran perfectly. I guess the new ones aren’t exactly what the GT40 likes. This once again proves, the last thing I “fixed” is the first place to look. |
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Jonny Quest
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Posted: June-14-2022 at 10:44pm |
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Current
2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
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KENO
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Posted: June-15-2022 at 7:42am |
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Good thing you didn't "fix" the distributor .
If you were to decide to get one as a spare, try the Spectra FD-14 from Rock Auto, you'll probably like the price, even after shipping charges. How's the fuel pressure when it idling now? And.............good job on the diagnosis
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skeet
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Posted: June-15-2022 at 8:14am |
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Since the Spectra is known to work, that’s the way I’ll go when needed.
Thanks for all the input. I wish I had started a build thread on this one. I restored it over the winter. New decals after gel coat work and wet sand/buff. New skins from C&S. New rub rail. Painted wind shield frame. New stereo. Perfect pass. Restored gauges and dash. Wood steering wheel. C&S was great to work with but upholstery work is not fun if you’re a perfectionist. Now if I can get the slalom course straight it will be a fun summer. |
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MrMcD
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Posted: June-15-2022 at 12:21pm |
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Nice work on the repair, since you have a fuel pressure gauge you might leave it hooked up after you run the engine. Turn the engine off and watch your fuel pressure to see if it holds. It should hold pretty close to the running pressure for 30 minutes if it is sealed. If you lose 5 psi, no bid deal but if pressure drops quick you have a leak, at the injectors or at the fuel pressure regulator. I assume there was an issue or the new injectors would not have been purchased.
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skeet
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Posted: June-15-2022 at 12:28pm |
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Excellent idea.
Yes, the new injectors were purchased to address a hot start issue.
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agetech
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Posted: June-15-2022 at 2:41pm |
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Standard Motor Products injector FJ699 from Rock auto are $65 ea. Standard makes quality parts and I have a couple of these in my boat.
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KENO
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Posted: June-15-2022 at 8:23pm |
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By the way Skeet, since you mentioned the PCM handbook, assuming that's the 301 page gt40 manual, one thing to keep in mind is that that manual came from Ford and was written for the first versions of what PCM calls the gt40.
Those first versions a year or so before PCM started using the engine were the fuel injected OMC/Volvo King Cobra engines in 5.0 and 5.8 varieties used in stern drives. There are numerous places that the manual gives info that's dead nuts accurate for the OMC/Volvo engines but not too good at all on the PCM gt40 I wouldn't claim to be able to list them all, but some of the equipment locations are different, some wiring colors and diagrams are different and the fuel system description and diagrams are different like where they talk about the vapor separator reservoir. It's enough to drive a poor guy crazy sometimes
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skeet
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Posted: June-15-2022 at 9:03pm |
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I noticed the engine layout was a little different but I chalked it up to year differences. Thanks for the heads up. I need to take it and get it bound before it blows across the lake.
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skeet
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Posted: June-17-2022 at 10:50am |
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skeet
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Posted: June-17-2022 at 10:51am |
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My golden, Mason, really appreciates the help getting him back to his favorite place
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gun-driver
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Posted: June-17-2022 at 11:31am |
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So you replaced the old injectors because you diagnosed them as I assume leaking down causing the hot start issue.
Yet now they work??? This is the reason that steered me towards an ignition issue hence the check the distributor diagnosis as there has been issues PIPs going bad which can act like your symptoms. Just sayin’ |
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skeet
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Posted: June-17-2022 at 12:45pm |
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The boat always started with the old injectors. It would just sometimes exhibit characteristics of being flooded when hot.
I haven't had a chance to get the boat in the course and see how it does this year with repeated hot starts. I never put a fuel pressure gauge on it with the old injectors but now that I own one, I can. This should help me identify if I have a leaking injector.
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KENO
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Posted: June-17-2022 at 2:13pm |
Hey........it's a gt40 (but you can pick any fuel injected engine these days) and if you don't have a whole arsenal of diagnostic equipment you're gonna throw some parts and money at it, unless you get just plain ole' lucky. That's been shown with numerous gt40 issues over the years, here on CCF. I think the distributor qualifies as parts and money. Still wondering what your fuel pressure is at idle after the old injectors went back in Skeet |
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skeet wrote: