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1999 DF70 stumbling/surging around 3500 and will not rev past 4200 RPM

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fredk

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I just mounted an old DF70, 1999 ( in Evinrude colors) to my 5,1m center console. It starts and idles like new (as far as I can tell). Acceleration is good and it runs smooth until it hits 3500-3700 rpm where it begins to stumble/surge, there is still a lot of travel on the throttle at this point. If push the throttle further (to full) it stops the surging and smooths out but never goes beyond 4200 RPM. The throttle valve clearly opens as the intake noise increases but the rpm does not. No codes or beeps. I had a code 4-2 yesterday saying CKP was faulty but I measured all three sensors today and they all check out. 207, 208 and 210 ohm. No error code today after fiddling with the connector so it may have been some corrosion or oxide.

Also tested the neutral switch since the stumbling begins at 3500 rpm. Works OK, closed in neutral and open in gear. Starter will not engage in gear, as it should be.

It occasionally needs some throttle to start second time shortly after a cold start.

The motor lives in the Baltic sea so it has survived corrosion OK. Previous owner replaced the ECU since the old one was not operational.

New spark plugs and new low pressure fuel filter. I am leaning towards a fuel issue/restriction. High pressure fuel filter or maybe the fuel pump screen. I do not have any equipment to check fuel pressure unfortunately. Could an air leak in the fuel line from tank to engine cause this? We tested pumping the primer bulb during surging but no change.

The Evinrude manual also mentions the MAP sensor hose as a possible cause of low power, however symptoms also include rough idle and that is something I do not see.

As I pull back on the throttle it smooths out at around 3500 rpm and cruises along like nothing ever happened. I do not really need to go faster but for water skiing etc I will need more power. Not to add that the boat is impossible to sell in this condition (at least at a decent price).

Thanks in advance for any help on where to look next!
 

This video is based on a Honda outboard but it’s worth watching. This guys goes through the entire fuel system, obviously the procedure for Suzuki vs Honda will differ but the principle is the same.
 
Thanks for the tip, i will give this good look. Principally, the fuel injection works the same way regardless of manufacturer of course.
 
I have been through the whole fuel system incl fuel pressure test. Everything checks out.

Engine behaves like it is in neutral even when in gear. I have tested the neutral switch, 0,6 ohms resistance in neutral, no continuity in gear. Manual says 0 ohms in neutral and endless resistance in gear.

Is this an ECU issue or is the 0,6 ohms enough to trip the ECU to not notice the difference between open and closed?

No issues found by dealership on diagnostics unfortunately.

Anyone with experience on similar issues.
 
Is this the neutral START switch in the control box or the motor is RUNNING in neutral switch on the engine linkages?
 
It is the switch on the motor I refer to, the one that feeds into the ECU. Not the start in gear protection switch in the control box.
Yellow/green and brown leads on the diagram.
 
I’ve never had to mess with the sensors on my Suzuki. I’m surprised the dealer couldn’t pinpoint your issue. Did you test the Shift Position Sensor, I believe it’s tied into the Neutral Safety Switch, not sure but your service manual should tell you. I’m assuming you have a genuine Suzuki service manual?
 
I agree, I was also hoping for the dealer to figure it out.

The DF70 is Evinrude branded but it is all Suzuki except the stickers. And yes, I do have a PDF of the genuine Evinrude repair manual.
 
www.selffixer.com

Outboard Motor - Suzuki 9.9-70HP Four-Stroke 1997-2000 Shop Repair Manual

Suzuki 9.9-70HP Four-Stroke 1997-2000 Shop Repair Manual Manual covers the following models: DF9.9, DF15, DF 25, DF30, DF40, DF50, DF60, DF70 Manual chapters: General Information Tools and Techniques Troubleshooting and Testing Lubrlcatlon, Maintenance and Tune-up Syncronlzation and Adjustment ..
www.selffixer.com www.selffixer.com

I wonder if the above link is the same manual? One would think they are the same but stranger things have happened in the outboard world.
 
Hi! No the manual in the link is not the same as I have. Mine is specific for the 1999 Evinrude 60/70 four-stroke, equivalent to the Suzuki DF60/70.
 
More testing done. I have measure both coils with OK results.

I have also verified that the neutral switch is not the culprit. I did this by disconnecting the switch at the connector and replacing it with a jumper lead to enable starting. I then left the jumper connected as if it was still in neutral. I then only reach 3000 RPM as per the S.L.O.W spec. When I remove the jumper lead simulating motor in gear I can again reach up to around 3700 where the stumbling begins. More throttle gives me higher RPM , 4500 and over running in gear in a barrel (prop removed).

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Hence, the neutral switch is not the problem. It is not the CTP either, ignition timing is verified to increase up to 20 or 25 deg, not stuck at 5 deg btdc which would be the case if the CTP was malfunctioning.
 
Back to post #1 “Could an air leak in the fuel line from tank to engine cause this?” Can you see any air bubbles in the low pressure fuel filter? Air will cause running issues.
Have you checked the float in the VST? Could be that the float is allowing enough fuel to run at 3500 rpm but once you start advancing the throttle the VST can’t deliver enough fuel.
No codes to me would indicate that your issue isn’t sensor related, I’m fairly certain that every sensor has an associated code.

I’m just throwing ideas out there hoping something will stick.
 
Please keep the ideas coming, it is greatly appreciated!!

I will check the fuel lines, tank, pick-up tube as well.

The consistecy of when the hunting rpms start, always ar around 3500- 3700 rpm regardless of whether it is running under load or not indicates an electrical issue to me. If anyone disagrees please let me know.
 
William01 said:

This video is based on a Honda outboard but it’s worth watching. This guys goes through the entire fuel system, obviously the procedure for Suzuki vs Honda will differ but the principle is the same.
Click to expand...
Thank you. The video is very informative and gives me a good idea of what is involved. Would have liked a video showing the VST removal on a BF50 efi. Have looked everywhere without any luck. Will keep looking. Cheers.
 
fredk said:
Please keep the ideas coming, it is greatly appreciated!!

I will check the fuel lines, tank, pick-up tube as well.

The consistecy of when the hunting rpms start, always ar around 3500- 3700 rpm regardless of whether it is running under load or not indicates an electrical issue to me. If anyone disagrees please let me know.
Click to expand...
 
Hi Richard, no I have not been able to resolve the issue. Bought me an SDS to diagnose and discovered yesterday that is a fuel injection issue. Below 3500 rpm all is sweet. At 3500 the injector pulses begin to jump between 11000 micro seconds and 7000 micro seconds every 0,2 seconds. This causes the rev limiter behavior. In addition to this the rpm interval running time counter shows zero mins at idle. Total running time of 9 hrs 18 min and 494 minutes running over 5000 rpm. Complete nonsense and not reflecting reality.
 
Not as long as I have owned it. Checked the VST and it was like new. Fuel pressure is good. Previous owner said he replaced the ECU, do not know why. Also borrowed a complete fuel rail with injectors, made no difference. Cleaned my injectors as well. Always run 98 octane E5 with sta-bil fuel stabilizer and a small splash of 2-stroke oil to lube the pump.
 
Do you drain the vapour separator and if so how often, but if not have you ever drained it. You must do it weekly if you're using it frequently.
 
Never drained it but I split it open and it is pristine inside. I know for a fact the injection timing changes at 3500 rpm. Not VST related.
 
It's funny you say that, I work for Australian Army Marine and we see a lot of outboards with the same issue as you are having and 9/10 it's the VST, which holds the high pressure fuel pump. If that pump is starting to fail then you won't be able to achieve those higher rpms
 
fredk said:
Never drained it but I split it open and it is pristine inside. I know for a fact the injection timing changes at 3500 rpm. Not VST related.
Click to expand...
Compensating Sensors list battery voltage. Worth checking out. Screenshots are from a 2009 DF90A service manual. I’m on a Suzuki form and the ECM rarely act up unless poor voltage.
IMG_6318.jpeg
IMG_6319.jpeg
 
Thanks for your input, I do appreciate it! I also see the connection between low fuel pressure and not beeing able to get full engine power. However, I know from reading the log file from the diagnostic system that the injection time (and thereby the injected amount of fuel) is, for some reason, suddenly reduced when the engine hits 3500 rpm, it then varies every 0,2 sec. Injection time is controlled by the ECU, the VST delivers fuel at the correct pressure but the ECU refuses to open the injectors long enough to get more fuel into the cylinders to reach max rpm. WHY this happens is what I need to figure out.
 
Thanks for the input on voltage as well. SDS says I have around 14v in the ECU with the engine running, seem reasonable from the alternator. Voltage on the sensors though is unknown. I will go over the two common ground connections when I get the boat out of the water.
 
Great, I was on the road so I could not have a good look at the screen shots. They do give good guidance now that I have been able to review on a larger screen.

I tried to register on the Suzuki forum but it appears not to be active unfortunately.
 
I have a 1999 Evinrude 50hp. Mine was caused by bad cylinder temp sensor on top of cylinder jacket. and another time by bad o-rings on the fuel injectors. and another time by a bad injector.
 
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