1 engine revs slower than the other

[pwgsx]

The tank has 2 pumps in it, not much room or extra hose to swap. Man if the pump is bad it is going to suck big time. No clue how you would even remove the fuel pick-up and all since it only has about 4 inches of room till it hits the boat floor. Hoping my injectors or throttle body or idle valve is bad. Digging more into it tonight after work.

 

[Sportster-2001-951C-Stock]

I kinda doubt the pump is bad, usually when that happens the top end begins to suffer first. But, I don't know where the pressure regulator is located. On systems that dead-end at the engine and don't have a return to the tank the pressure regulator is located in the tank.

Did you notice if one of the spark plugs has any dark color on the center electrode insulator? If one of the injectors is leaking the spark plug may be darker with fuel soot.

Can you get intake manifold vacuum sensor pressure reading at idle speed, and ignition advance? Most ignition systems are timed off two proximity sensors on the crankshaft that are spaced differently so the motor can quickly determine which cylinder is at TDC within less than one revolution, and one of these sensors is also used for injector timing. Sometimes there's a camshaft sensor as well, used for injector pulse timing.

So if you have a chance look at candoo and make sure these crank and cam position sensors are pulsing data as the motor turns(runs), basically if all the sensors reporting similar data from both engines.

 

[Sportster-2001-951C-Stock]

Hey, something else to look for maybe... I had a guy pull up to our marina a couple years ago experiencing a similar issue and by scanning I found his engine knock counts were high and the computer was pulling ignition timing way back as a result. So I took a look at the knock sensor and found the bolt that held it onto the side of the engine block was extremely lose, causing the sensor to falsely detect knock and the computer responded by pulling ignition timing.

So take a look at your candoo engine knock count too while the engine's running, the computer will retard ignition timing if it thinks the engine is knocking.

 

[pwgsx]

I will take a look. Ok so I tested the engines yesterday and the port engine was still revving low. I swapped out the fuel injectors and railand now both engines seem to be revving a lot better. This is out of the water so I need to lake test. Very odd but maybe it is just tricking me so I am not holding my breath. Also when I throttle both engines seem to still cough a bit, idle to 1500 and then take off. At least the rpms seem to be together now. Not sure if this means anything till we take her out maybe sunday. I will keep u posted.

 

[Sportster-2001-951C-Stock]

If both are coughing intermittently then I wonder if there's any chance you might have a bit of water in the fuel tank?

 

[pwgsx]

Or old gas. Going to ride it till empty sunday. Other than that I swore I saw a black bit fall out when I dumped out the fuel rail of gas on the driveway but I couldn't find anything but a rubbery ball. Fingers crossed.

 

[pwgsx]

Ok went to the lake today and the issue is still there. You can see from the 2 videos, the left engine does not even respond much till more throttle is given. When in the water though some things I did notice- When the throttles are both at 3/4 open or even at WOT, both engine rpm's are dead even. The boat tops out at 52-54 mph's. As soon as I back the throttles off though to 4-5,000 rpm's the left engine does not stay even with the other. I could not hit WOT in the video bc the lake was pretty crowded but hopefully you guys can see whats happening. Out of the water is the same, cant run them for long but you can see how uneven they are.

https://www.youtube.com/watch?v=buANbMSU5nA

https://www.youtube.com/watch?v=khzmE-ksDnQ

 

[pwgsx]

Also would a idle control valve, MAP sensor or TPS have anything to do with this? I have reset the TPS and the MAP is reading correctly with the engine off.

 

[devonte007]

I re-read the posts again and watched the videos, which helped. As I understand, ever thing you have done has had negligible results solving the problem, correct?

Side note - I can’t believe that the candoo cannot be used while the engine is running to monitor different aspects, seems like that would be a key advantage to having a diagnostic tool such as that. I feel that I have heard of others using it while the engine was running. Have you tried contacting them to find out for sure, people say that their customer support for the product is good.

Back to the issue at hand…port engine:
Seems to start and idle perfect but will not increase speed smoothly. I noticed that engine will jump from idle to about 6000, seems there is no way to smoothly and slowly increase rpms. Is this true for the whole rpm range? In other words if you slowly advance the throttle, is there any rpm range that is consistently not smooth or consistently smooth? Is the engine rpm more controllable in the higher range more so than lower range? I am guessing the answer is no, and that the engine is equally choppy no matter where you advance the throttle from or where you stop.

If so I have a theory that there may be some type of mechanical issue with the throttle either from a gummed up throttle body (unlikely) or a broken throttle cable. From what I witnessed in the video seems like the throttle is on a rubber band, you increase throttle and nothing happens until –bam- it snaps back and rpm’s jump rapidly. On a car I have witnessed this if it is gummed up, takes lots of pressure to move the butterfly and it suddenly then snaps open near half throttle. If the cable sheath is impaired (either at throttle levers or throttle body) it can act kind of like this. It would also behave differently when not started (not under load) and when running (under load of vacuum pressure). Simple test would be to stick your hand into the throttle body (engine not running) and put some pressure on the butterfly valve with your fingers, ask someone else to slowly increase throttle while you feel if there is any play or if the butterfly moves smoothly in relation to the throttle even with pressure applied. Any detectable play in the cable? May want to inspect the cable at the throttle levers too.

Kind of a shot in the dark and a way out theory, but all I can think of right now. As for your question about the idle control valve, it does not seem like it can cause this type of issue. The IDC really only affects idle, that’s it. Since the boat starts and idles perfect then it is unlikely to be bad. It is simply a small servo motor that controls a trap door on the side of the throttle body to let air in and control idle when the main throttle butterfly is closed. The computer controlled motor opens and closes the idle butterfly to keep engine idle constant regardless of load, temp, etc. It seems to be doing that so probably not the problem. The other sensors in the throttle body can be hard to test, especially the MAP. Usually if the MAP is bad then there are significant runability issues and you will get a check engine light. Since you have swapped/replaced just about everything else it seems very likely something to do with the throttle body.

Sorry if this does not help much, if I come up with any other nutty ideas I will let you know!

 

[pwgsx]

You are correct, the rpms stay at 2500 -ish on that one engine and then will sharply jump to 4500-5500 in a snap. After that if I increase both throttles more, the difference between the two become less and by 6500-WOT they are both dead even. I will check into the butterfly and throttle when it is moved and see how it opens and closes. In my few days of searching every forum known to man, the idle control valve seems to only be a idle and low rpm issue but I cant rule that out all the way as they same some get stuck. The MAP is suppose to throw a code if its bad but read some just don't read correctly- doubtful that's my issue but I will try it. Lastly the TPS seems to be a common issue and most say it affects idle, low to mid range rpms, stalling, hesitation, erratic throttle response which kinda falls into what mine is doing although they have been reset and seem to read correctly with the CANDOO, but maybe when the engine is running it is messing up.

As of now my plan of attack will be since these are easy enough to swap parts. Check butterfly and cable movement, swap MAP sensor, swap idle control valve, and lastly the TPS. Not sure how far I will get, it has been 100+ here for the last week and digging in a boat just SUCKS I have not ruled out fuel pressure or have done another compression test but with the engine topping out where it should I kinda ruled those 2 out for now.

As far as the candoo, I thought I could run the engine with it connected but mine wont turn over. Tried it on both engines. They said there is too much interference but a new update coming out should fix that.

 

[Sportster-2001-951C-Stock]

As far as the candoo, I thought I could run the engine with it connected but mine wont turn over. Tried it on both engines. They said there is too much interference but a new update coming out should fix that.

Perhaps the candoo sample rate is too demanding and if they reduce the rate they can allow you to start and run the engine. Pretty basic stuff though, to be capable of monitoring a running engine.

The very best way to test an variable resistance type of TPS involves using an analog voltmeter to backprobe the potentiometer wiper signal and watching the meter needle swing, the voltage should be smooth and not choppy with dead spots. Dead spots make the engine controller think you closed the throttle, thus the computer responds accordingly to an erroneous signal.

But since you have candoo, you can easily swap the other TPS and recalibrate.

Could also be your throttle cables are binding for whatever reason, they should operate the throttle body butterfly smoothly.

Wonder if the next iteration will include fly by wire simply for the purpose of making life even more complicated?

 

[Sportster-2001-951C-Stock]

Oh, and the engine controller may have a strategy for "parking" the air controller in a position greater than idle so that the engine doesn't run out of air and stall when the throttle is immediately closed.

Not trying to say I think your idle air device is creating an issue, I have seen them gummed up with fogging oil during a particularly zealous winterization though.

MAP sensor - You can monitor the output of this device as well by using a voltmeter to measure the voltage signal output while the engine is operating, then compare this voltage to the table I'm certain is in the service manual to determine the manifold pressure. This is the harder way to do it when there's no diagnostic tool such as candoo, available.

 

[pwgsx]

I scored a new TPS on ebay for $30. Figured it was less trouble than having to remove both throttle bodies, remove, re-install and reset them. This way I know its good. It should be here Fri. I will let you know if I get to swapping the MAP sensors for the hell of it or check on the rest of the throttle body inspection.

 

[Sportster-2001-951C-Stock]

Yeah man, it's really not a bad idea to have spare sensors on hand anyway. I had a guy bring his Evinrude in saying it would just up and quit on him out in the bay and he was getting tired of taking it to the other shops who couldn't find any problems so did nothing.

I hooked up my scanner and found it had a TPS sensor fault so measured it every way I could think of and found nothing so swapped it anyway with a new one and never heard back from him. I hope that fixed it for him. I figured he just wanted the problem to go away so it was worth spending the money and taking a shot since nobody else had.

 

[pwgsx]

Well I got around to removing the throttle body and planned to replace the TPS and re-install........BUT things never go as planned. The TB is VERY dirty. You can see all the gunk built up inside of it as well as the corrosion from when it was used in salt by the P.O. . I plan to get some TB cleaner today and get it looking like new. The Idle Bypass Valve seems ok, it was extended and not pushed in ( I saw from another thread squished means its bad and extended its good ). The butterfly was not sticking even with all that gunk so I doubt the gunk is the problem. Is there any special care I need to take or just spray and clean away? I know not to turn the idle screw so I will be leaving that as-is. I guess I need to clean the other engine as well

 

[Sportster-2001-951C-Stock]

I agree, doubtful the crud is causing harm, I've seen much dirtier TB's than yours still working fine! Mostly these are engines with exhaust gas recirculation into the intake and can eventually cause the butterfly to stick slightly open so it doesn't return to idle.

If the engine cannot control idle speed then we can suspect the idle air bypass valve isn't working smoothly or a sticky throttle. Sometimes oil and trash can get into the idle air valve, often when they break or wear out it's b/c the computer constantly moves it under normal operating conditions. Some IAV's are made better internally than others and last forever while others can be a little fragile and easily damaged. The one you have there looks similar to those GM uses, it might even have been made by Delco.

 

[pwgsx]

IF the rain holds off tonight I will get the other TB removed, both cleaned and new TPS installed in the troubled engine. Since I can easily remove the IAV I will swap them last if the problem still occurs. When I clean the TB, I should be able to spray everything down with cleaner after the TPS and IAV are removed right? There shouldn't be anything else to damage?

 

[Sportster-2001-951C-Stock]

IF the rain holds off tonight I will get the other TB removed, both cleaned and new TPS installed in the troubled engine. Since I can easily remove the IAV I will swap them last if the problem still occurs. When I clean the TB, I should be able to spray everything down with cleaner after the TPS and IAV are removed right? There shouldn't be anything else to damage?

Yeah, you'll be fine if you keep the solvent out of the electrical parts, some of those can be damaged by solvents.

Some throttle bodies had a special polymer coating on them for some reason, thus we now have throttle body cleaner.


I think the nose of the IAV pintle looks clean, dirty ones have crud all over the plunger tip and bypass throttle body passage.

 

[Sportster-2001-951C-Stock]

BTW, I dunno if you'll need to replace the IAV (kinda doubt it) but you might save $$$ by matching it with the same part from a GM vehicle.

The Honda ski guys have found car parts are identical in several instances, seems Honda Marine used some sensors from their vehicle division.

 

[swissdoo]

you are focusing on a engine or control problem. Ever thought it could be a mechanical issue? If one wearring or impeller is bad this engine will rev faster. Do a gps speed check on each emgine, i bet one will be faster... Patrick

 

[pwgsx]

Stopping for some throttle body cleaner on the way home and will look into the GM parts too for a possible replacement if needed.

Swiss- I already rebuilt both pumps and seals, the problem still occurred. At this point I am 80% sure the problem lies within the throttle body. I have swapped out almost every other item from the other engine. Something is making the engine lag and at a certain throttle position it takes off like a rocket and evens out with the other the higher you go on rpm's.

 

[Sportster-2001-951C-Stock]

The IAV that is assembled with 3 rivets seems to be the good one, SMP aftermarket makes one that's crimped at the connector end instead of the 3 rivets and those are junk.

Looks almost like this AC165 from a Chrysler except maybe for the connector?

 

[pwgsx]

That car part looks very close to it........... I was able to clean the TB and swap out the TPS. The only thing I could see that didn't look great was a lot of crud under the sensor that got past the green o-ring. I didn't see anything in the actual sensor but it has me thinking that maybe some salt water or moisture got in there and messed it up at some point but who knows. IF the new sensor fixes it, I will take the old one a part and find out. Other than that and the little bit of crud on the TB itself, it cleaned up well. Hope to re-install the TB's tonight and get the CanDoo to zero them out.

 

[pwgsx]

Got both TB's back in the boat, reset both TPS's and got 0-84.9 and 0-80 on the other (I think I know where my 500 missing rpms are) . Started both engines, they idled rough at first, shut off and restarted and seemed to be good. It was hard to tell but the problematic engine seems to be responding to the throttle being moved to any position now and was smooth and not choppy. Need to get it on the water to know for sure.
Took the TB back off and checked to make sure the cable was tight but not too tight. All seemed good. Hooked up the candoo again and reset the TPS but still only got 80. If I move the lever by hand I can reach 85. I set the throttle all the way open and I can see the throttle plate not opening all the way. The other is perfectly horizontal, this one is 90% open. I cannot get any more out of the adjustments on the TB side to make it open more so I "think" I will need to adjust the cable on the throttle side?? Does that seem correct?

 

[pwgsx]

Fixed

:thumbsup: Well the TPS was the problem and all the headache. The boat ran like a top for the first time since I purchased it, hit 52 on the gps with both engines responding to the throttle movement

Now only a small problem, I adjusted the throttle cable as much as I could at the engine but the TB wont open up all the way- still missing 500 rpms. I have a feeling the cable on the throttle side needs to be tightened BUT as always I ran into a snag. The 4 screws holding the whole housing on are corroded and stripped. I am assuming I will have to drill the heads off and drill new holes. Do you know if these screw into just fiberglass or a metal plate?