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Help Chasing Erratic Idle Please

Old 04-20-2019, 08:31 AM
  #51  
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My manual 16 page 1B-4 and I'm seeing 37 psi with motor running, but 1 psi should not cause the issue your seeing.

I went back and read thru the entire postings (quick read) again to refresh memory. I am subscribed but didn't get notification on this one

The idle and extra fuel (black smoke) comes and goes. Disconnect TPS and reconnect and all good for a short time, then its back. Swapped ECU's and no help. Does resemble a bad connection and could be that or intermittent sensor. Has the MAP been looked at?

Edit: retract, I did get notified

Last edited by AllDodge; 04-20-2019 at 08:36 AM.
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Old 04-21-2019, 08:34 AM
  #52  
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Originally Posted by AllDodge View Post
My manual 16 page 1B-4 and I'm seeing 37 psi with motor running, but 1 psi should not cause the issue your seeing.

I went back and read thru the entire postings (quick read) again to refresh memory. I am subscribed but didn't get notification on this one

The idle and extra fuel (black smoke) comes and goes. Disconnect TPS and reconnect and all good for a short time, then its back. Swapped ECU's and no help. Does resemble a bad connection and could be that or intermittent sensor. Has the MAP been looked at?

Edit: retract, I did get notified
Thanks

I agree with your manual, see my post above (#50) as per my fuel pressure gauge is very low but it's that way on both engines and the other runs fine. Both engines also don't exhibit any issues under power, if anything I'm rich according to transom soot after running it. Maybe the injectors are having to dump fuel to keep up with the a potential failing fuel pump? I'm going to source a new gauge and retest.

The black smoke issue was solved. The original surge just off of idle still exists as well as, random stalling (from idle) and not wanting to run at anything below 1200 rpm on the hose.

I agree with a bad sensor, here's what I've done to date.
IAT- swapped from good engine to bad, no change.
ECT- new, no change.
TPS- new, no change. New harness corrected black smoke issue.
MAP- swapped from good engine to bad, no change.
IAC- on my 4th one, no change.
ECU- swapped, no change.
Ignition Coil- swapped, no change.
Plugs, wires, cap and rotor are new, no change.
Fuel lines are not restricted.
VST- Was rebuilt and yellow lines replaced, no change.
New mechanical fuel lift pump, no change.
Checked throttle body plate and linkage, no change.
Base timing it correct.
Manifolds, risers Y-pipe flappers are new.

Tested all sensor side harness pins as per the manual and they're all fine. ECU pins and harnesses are pristine. Ran the "Rough, Unstable, or Incorrect Idle, Stalling" procedure from the manual and all checks out per spec.

In a previous post I did note that when pulling the vacuum line from the FPR on the suspect engine the surge went away, i.e. revs. stabilized.

I run non-ethanol pump gasoline.
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Old 04-21-2019, 09:18 AM
  #53  
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Originally Posted by Tractionless View Post
Thanks

In a previous post I did note that when pulling the vacuum line from the FPR on the suspect engine the surge went away, i.e. revs. stabilized.
This increases fuel psi.

When you pulled the line off for this, did you plug it with your finger tip or etc to block off air leak?
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Old 04-21-2019, 09:20 AM
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Some odd thoughts

Does the throttle linkage just connect to throttle plate or does it help close the plate?
Is the throttle plate fully closing?
Remove the throttle linkage and see if the plate returns. Try a few times to slowly allow the plate to close and does it return to the same position without assistance.

Ground connection between
Injectors tested?
Has a vacuum gauge been used to measure intake vacuum?
Is compression equal across cylinders?

Other then that I go back to connections in post 15
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Old 04-24-2019, 06:50 PM
  #55  
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I had numerous issues that seem like yours, most all came back to the vst. Poor idle, surging, black soot, raw fuel coming out exhaust. Rebuilt vst numerous times, clogged screen in the bottom of it, new pump, ruptured diaphragm, all less than 10hrs in between problems. Last straw was poor idle and dumping raw fuel out exhuast. If it is same vst as my 502 check big black hose that comes out the side and dumps it into plenum. I connected a longer hose to it and ran it to container then fired up the motor, fuel was pouring.out...

Last edited by camptappakeg69; 04-24-2019 at 06:56 PM.
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Old 04-24-2019, 07:01 PM
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It was dumping all that extra fuel into the plenum, would run great above 1500 or so but would idle like crap.... ended up plugging the port after removing the vst .

Last edited by camptappakeg69; 04-24-2019 at 07:06 PM.
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Old 04-26-2019, 11:05 AM
  #57  
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Originally Posted by SB View Post
This increases fuel psi.

When you pulled the line off for this, did you plug it with your finger tip or etc to block off air leak?
Yes

Originally Posted by AllDodge View Post
Some odd thoughts

Does the throttle linkage just connect to throttle plate or does it help close the plate?
Is the throttle plate fully closing?
Remove the throttle linkage and see if the plate returns. Try a few times to slowly allow the plate to close and does it return to the same position without assistance.

Ground connection between
Injectors tested?
Has a vacuum gauge been used to measure intake vacuum?
Is compression equal across cylinders?

Other then that I go back to connections in post 15
Throttle linkage does not hold the plate closed and the plate closes fully. I tried to close more while running and it does not. It closes on its own and operates just as the other does.

Ground connection for injectors not tested, I will do it.

I have not checked vac. Nor compression. I'll start with vac. And post back my findings.

Originally Posted by camptappakeg69 View Post
I had numerous issues that seem like yours, most all came back to the vst. Poor idle, surging, black soot, raw fuel coming out exhaust. Rebuilt vst numerous times, clogged screen in the bottom of it, new pump, ruptured diaphragm, all less than 10hrs in between problems. Last straw was poor idle and dumping raw fuel out exhuast. If it is same vst as my 502 check big black hose that comes out the side and dumps it into plenum. I connected a longer hose to it and ran it to container then fired up the motor, fuel was pouring.out...
I will check into that thanks!
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Old 04-26-2019, 12:49 PM
  #58  
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After your prompting on other thread, seeing as you pull vacuum line from FPR and issue cures itself, could you have a collapsed/pinched vacuum line that is closing off and is holding vacuum to regulator on occasion? Cheap enough to just replace that's for sure.

Have you had injectors cleaned/tested? You should have the older Kehin injectors I imagine. Regardless, they should be checked. With vac line pulled and pressure increases, the engine then runs fine? Sounds like it is still somehow running lean then. Fuel pressure may be good but if you have clogged injectors or intermittent sticky injector, computer and IAC just don't have enough compensation.

I'll be the first to admit I had to learn the hard way with a burnt/detonated piston about how bad the Merc fuel injectors are over time....

You say no hot start issues above? When I had FPR issues, my engine was a beeotch to restart and get to idle when hot, but again mine are also Cool Fuel and not VST. Personally, I'd get rid of the VST since they are so problematic.

Last edited by Gimme Fuel; 04-26-2019 at 12:52 PM.
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Old 04-27-2019, 01:57 AM
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FUEL INJECTORS and those same injectors are even used for the hp 525 as well. Those exact injectors have issues and all have one common problem that takes place in due time. ALL of them whether one thinks so or not. I have fixed many to know all the issues with marine fuel injectors especially those injectors. .

So let me say this for boaters with fuel injection engines - maybe something to really think about for whomever - A Carb is a fuel delivery item but is ONLY a Mechanical fuel delivery item again ONLY a mechanical fuel delivery item - in due time all carbs need cleaning along with new rebuild kits installed to take care of the issues that happens internally -- especially carbs with 25 years of marine use.

So moving on to fuel injectors - they are fuel delivery item AS WELL.. But lets keep in mind they are Mechanical and ELECTRICAL fuel delivery items so with that said alot of other issues can happen from one side or both sides of what and how they deliver fuel. So with that said -- Seems as alot of people think that fuel injectors never go bad nor need attention nor need cleaning with new kits installed, especially 25 year fuel injectors that have electrical signals running thru them basically along with high pressure fuel passing thru them plus fuel sitting in them 24 / 7 - 365 days for many years if not 25 - 30 years ??

Also keep on mind the pintle holes in fuel injectors are way smaller than anything in a carb to deliver fuel. Fuel injectors are maintenance items and not done especially NEVER will cause running issues and engine failures.

When was the fuel injectors professionally serviced in your app ? Not trying to sell this but its all fact about fuel injectors. .

Last edited by BUP; 04-27-2019 at 02:13 AM.
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Old 04-27-2019, 02:03 AM
  #60  
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From POST # 58 GIMME FUEL -------- Have you had injectors cleaned/tested? You should have the older Kehin injectors I imagine. Regardless, they should be checked. With vac line pulled and pressure increases, the engine then runs fine? Sounds like it is still somehow running lean then. Fuel pressure may be good but if you have clogged injectors or intermittent sticky injector, computer and IAC just don't have enough compensation.

I'll be the first to admit I had to learn the hard way with a burnt/detonated piston about how bad the Merc fuel injectors are over time....

FROM ABOVE POST # 58 ^^^^^^^

BINGO WE HAVE A WINNER he knows and understands exactly what I say up here at least every 2 weeks. Marine fuel injectors will always need servicing, really do not care if one or millions do not think so but I will say never had a set of 6 or 8 fuel injectors come in that did not need something and many needed alot cleaning and testing in many forms to bring back to new performance. . They all need cleaning of some sort and many have electrical issues as well. They all are maintenance items but is never thought of or forgotten by many. Take for its worth by whomever.

Last edited by BUP; 04-27-2019 at 02:11 AM.
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