Lack of Power - Miss/Stumble Below 3000 RPM


Information and questions on GL1200 Goldwings (1984-1987)
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Rednaxs60
Posts: 2342
Joined: Wed Nov 18, 2015 12:44 pm
Location: Victoria, British Columbia, Canada
Motorcycle: 1985 GL1200 LTD
1995 GL1500 SE CDN Edition
2012 Suzuki DL1000 VStrom
2008 GL1800 (sold)
Ontario 1985 GL1200 LTD (sold)

Lack of Power - Miss/Stumble Below 3000 RPM

Post by Rednaxs60 »



Thought I'd document the last two months regarding subject issue and my "85 1200 LTD. It is a long report as it is compiled from another forum that I kept updating. My hope is that it will provide useful information for the other '85-'86 FI bike riders. Here's my story.

Preamble:

Went for a 4 day tour of our lovely BC province with a very pleasant passenger. Took the '85 LTD of course as I have been working on it to get it so I could tour with it. All went well, bike ran well, and it was lovely weather. Went through Trail, BC then headed up the mountain to Rossland, and on to Strawberry pass that is about a mile up. All was going well but I noticed the bike was staring to run hot.

Started through Strawberry pass and lost power. Bike would start but would then quit. Baffled me and the only thing to do was to let it sit and contemplate a strategy.

I let it sit for some 45 minutes or so, but during this time I was able to start it but it would stall immediately. I noticed the fuel pump sounded different as if it was cavitating.

After letting it sit and cool down, started it up and it sounded not bad and kept running. Made the decision to carry on. Sonya was a bit stressed but not a lot we could do.

Rest of the tour went well, and we made it home on day 4 as planned. Also did another 4 day tour of BC with my HD friends and the bike operated well, but I did notice a change in how it performed off the line. Since nothing was earth shattering at the time, I continued and had a great tour.

Discussion:

Now for the mystery. These fuel injected bikes are extremely power sensitive and need a lot. I had noticed that the voltage showing on the dash gauge would reduce as the rpm got higher, but return to 13.8 VDC (14.4 VDC at battery - only look for consistency when it comes to gauges). I noticed today that it was consistently 13.8 VDC and the bike was operating well and the sound of the engine was as I expected.

I have the alt mod on my '85 with a pulley ratio of 1:2 - 4' pulley at crank and 2" pulley on alt. I have read where alternators operate in a range up to approximately 9K RPM. I also know that alternator output is not linear, in that an alternator will go to full output say around 6K to 7K RPM then start to fall off. With the charging systems designed today, if one of the components of the charging system is not keeping up then you can have issues. I'm thinking that the alternator RPM was such that I was actually discharging the battery as I was keeping the RPMs high because I was travelling two up through the mountains.

It was mentioned in another post that the RPM should not affect the alternator and as such I will monitor and if necessary, look further into any issue with the alternator.

The other aspect of this issue is the fuel pump and how it sounded when the bike first quit. It was very peculiar and I had not heard it sound this way before. I will be doing a fuel pressure test and looking at the fuel return/venting system. Have a fuel pump on hand

When I had the issue with the bike in Rossland, The rise was close to a Km in height. Something to keep in mind regarding operation of the bike.

Since this happened I changed the fuel pump to an Airtex E8312. Bike seemed to be operating well after the change and I went for another 2000 Km tour around BC with two of my HD friends.

When I came back from the second tour, started to notice a loss of power at the lower RPMs, specifically below 3000 RPM. This continued to worsen so I took the '85 off the road and took to riding my 1800. Always good to have a second bike.

I started to troubleshoot the bike and did the following over a two month period:

1. Replaced the Airtex E8312 fuel pump with a Spectra SP1186. The Airtex pump is for in tank use, whereas the Spectra pump is for external tank use. Expect that the Airtex pump requires cooling from the fuel. No discernable change noticed at low RPM;
2. Replaced the coils and wires with aftermarket non OEM parts in late June. Saw some improvement then, but nothing discernible;
3. Looked into the various sensors that are ion the fuel injection system, Did a lot of research and on the CX500-650 forum, there was information regarding the PB (MAP) sensors and how these affect the system below 3000 RPM. The vacuum that the PB sensor(s) monitor is at maximum around the 3000 RPM range. Once the engine RPM is past 3000 RPM the PB sensor(s) are no longer in play. This forum found that the Suzuki MAP sensor is: Brand: Denso.
Type number: 100798-5630. Suzuki number: 15620-35F00. Suzuki description: Sensor Boost, IAP (Inlet Air Pressure) sensor. More to follow on this later;
4. I went home to Ontario and brought back the TPS, PB sensors, Gr/Gl (camshaft) sensors to do a repair by replacement to try and isolate the issue. Did not bring the Ns (crankshaft) sensor because I did not have the time to take the front off the bike;
5. Took the alternator in for testing, only needed the bearings replaced;
6. Had replaced the injectors with aftermarket Autoline 16313. Worked well but I had the original injectors cleaned/flow tested and I put these back in when I got back mid July;
7. I found a Poorboy crank pulley for $40.00 USD. Had an issue finding a serpentine belt of the appropriate length so I will be staying with the existing setup for now; and
8. Had the battery load tested – tested good;

During my troubleshooting, I was torn between fuel and electrical. This was further aggravated by the lack of error codes on the ECU.

I replaced the sensors one at a time to determine if the issue would go away. No joy on any change. Did do the checks on the original TPS, and it was out of spec so I replaced it with the new to me TPS from the bike in Ontario. It checked out good and I set it up as per the manual specs. Having done this still no joy.

I checked the continuity and resistance to ground of the installed Ns sensor and it was out of spec. The original had been replaced with a 1500 sensor, so now to find something that would work. I found a post over on Steve Saunders forum where a fellow with an '85 LTD used the PG sensors from an '85 ASPY and it worked well. I found a new '85 ASPY/Interstate PG harness on the internet and bought it. I prepped the bike for the new Ns sensor install. I installed the new PG sensors as soon as I received. Both were installed over/under the crankshaft but I only have one hooked up. The second will be a spare just in case, and I won't have to take the front off the bike to change sensors, just change the connector under the shelter. Put the bike back together and road tested, still no change.

Installed the Suzuki MAP sensors in place of the PB originals. The bike operated the same, no change in the miss/stumble I was experiencing on the bike. The fellows over on the CX500-650 forum found that the PB sensor affected the CX500-650 bikes up to 3000 RPM (these are the FI models) and replacing this sensor corrected the fault.

I also checked a thought that was mentioned about the Gr/Gl (camshaft) sensors. Apparently the engine will operate with either the Gr or Gl sensor not working. I tried this theory on the PB sensors and the engine will stay running when one is disconnected (simulating an inoperable sensor). Good to know as a test for the PB sensors.

While I was waiting for the PG sensor harness to arrive, I painted the timing belt covers as these were pitted and the wear was through the clear and paint coatings. These turned out well, and when installed
look good. Since there is not a lot of the covers showing behind the fairings, I will not be doing any more to them.

After having done all this work, researching of the various forums, and perusing the service manuals, I was no closer to isolating and identifying the issue at hand.

Solution:

I remember an issue I had with my '65 Plymouth Fury back a few years. Drove to a friends house and did a tuneup, points/plugs/condenser/cap/plugs. After I was done I went to start the car and it would not. I had done this type of service many times in the past and it befuddled me. Started to go down the rabbit hole, changed out several parts with spares I had, and still no joy. Called my father several hours later and he simply stated go back to the beginning. What had happened was the condenser wire where it connected to the points had turned ever so slightly that it had grounded to the body of the distributor. Fixed this and it started immediately.

With this in mind, no error codes, and good fuel system pressure, I thought about what I had previously done. The two items replaced that could affect low power and result in misfires were the fuel pump replacement and coil/plug wire install. I ruled out the fuel pump because of the fuel system pressure was in spec – 38 PSI with key on/36 PSI at idle.

I decided to replace the new coils/plug wires with the old original OEM coils/plug wires. Before installing the original coils/plug wires I checked the resistance of each coil and one coil was considerably less than the 300 ohms required. This was checked when the coils were cold, and I expect that once the defective coil started to heat up the resistance would drop even further causing the miss/stumble issue I was experiencing.

I have the original OEM coils/plug wires installed and am pleased to say that the miss/stumble at low RPM is gone.

Prologue:

Now that the engine is operating as it should, I balanced the two cylinder banks, adn checked the compression.

The engine compression at cold was 125 PSI across the board. The compression is supposed to be in the 155 to 215 PSI range so I will check again but have the engine at operating temp.

There is a silver lining to everything, and this time is no different. I managed to get a few more items looked at and checked such as the fuel system pressure and engine compression. I cleaned up and painted the timing belt covers, looks so much better.

I had to replace the Ns and TPS as both of these were out of spec. I also have the other spare sensors on hand just in case.

I left the Suzuki MAP sensors hooked up until after the issue was resolved and can say the engine operated well with these installed. One of the issues with these Suzuki MAP sensors is that these sensors are a few years ahead in technology. The fellows over on the CX500-650 forum have taken a defective PB sensor apart and have found the internal connections to be less than adequate. I have; however, removed the Suzuki MAP sensors and reinstalled the original OEM PB sensors. I now have a few spares just in case.

I have learned more about the FI system and how it interacts and what each sensor does. This is a plus with these older FI bikes.

This has been a long report, but it kept me thinking for the past two months on what could be the issue. Thankfully, as I have mentioned, I had another bike to use that took the edge off my frustration with not identifying the issue sooner.

I've probably missed some details, but suffice it to say, The 1200 is out of the garage and on the road. Now to wait for the next challenge.

Cheers


"When you write the story of your life, don't let anyone else hold the pen"

Ernest

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Rusty Bike
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Location: New castle, PA
Motorcycle: 86 GL1200 SEi, 98 Valkyrie Std, 78 Yamaha XS750SE, 86 Honda XL125, 4.5 HP belt drive Minibike my dad built, foot clutch!

Re: Lack of Power - Miss/Stumble Below 3000 RPM

Post by Rusty Bike »

That sir, is a wonderfull story. I just rebuilt my old Mity-vac last night so I can test the PB sensors. Now it holds vacume. One step at a time. I'm taking the Valkyrie for a ride here in a few minuits. Thanks for the input. Arn't fathers wonderfull... :D

User avatar
Rednaxs60
Posts: 2342
Joined: Wed Nov 18, 2015 12:44 pm
Location: Victoria, British Columbia, Canada
Motorcycle: 1985 GL1200 LTD
1995 GL1500 SE CDN Edition
2012 Suzuki DL1000 VStrom
2008 GL1800 (sold)
Ontario 1985 GL1200 LTD (sold)

Re: Lack of Power - Miss/Stumble Below 3000 RPM

Post by Rednaxs60 »

Thanks Rusty - to check your PB sensor(s) just disconnect at the green and white couplings one at a time. If bike continues to run, PB sensors are good. I put a vacuum gauge on the PB lines and it showed between 10 and 12 in of HG at approximately 3000 RPM - max vacuum for these sensors.

Cheers
"When you write the story of your life, don't let anyone else hold the pen"

Ernest

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Ohara
Posts: 100
Joined: Mon Nov 16, 2015 9:05 am
Location: Ontario Canada
Motorcycle: 1986 Interstate
1986 Aspencade

Re: Lack of Power - Miss/Stumble Below 3000 RPM

Post by Ohara »

Good work, very dogmatic, :D Thanks for sharing.



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