Making it worse? Frustrated

[Guest]

Hello All,
Bought my '85 LTD back in March. Hesitates and "clunks" when I first accelerate like the key was shut off and turned back on, 'specially after she warms up. I wrote a post to this effect and have been following the advice of you knowledgeable folks.

I bought an analog meter to test the TPS (again). Smooth as can be. HOWEVER the resistance is 2.9kohms instead of the 4-6kohms stated on the tech index. Could this effect that hesitation? I bought a fuel pressure tester from Harbor Freight and my fuel pressure WAS right on. Now after the bike has been covered up for a few days, the fuel pump wont come on, and the computer unit doesn't cycle. I don't think the fuel pump just died, and why would the computer just stop cycling? I will test the fuel pump by direct wiring to the connector on the rear fender.

Seems like I've stopped cycling, but I'm not giving up.
Any ideas?
Thanks in advance,
Les

[roscoepc]

Now after the bike has been covered up for a few days, the fuel pump wont come on, and the computer unit doesn't cycle. I don't think the fuel pump just died, and why would the computer just stop cycling? I will test the fuel pump by direct wiring to the connector on the rear fender.

Try checking the Kill switch. If it's been bumped from run to off the fuel pump won't run, the dash lights won't cycle like they are supposed to, and the air pressure display won't function.

As far as your TPS, I've never messed with mine although I had a simular problem with the bike having a hesitation while in 1st at a slow speed and then accelerating for about a year after I got mine running. I think it was more of a problem with the injectors being a touch dirty than a problem with the TPS.

I'm assuming that 2.9kohms is your low reading. What was the high reading? I think that the TPS is adjustable but you'll have to grind off the breakaway bolts holding it to find out for sure...

[Guest]

I'm not a "fuelie" owner. I don't have an injected bike in front of me. I'm going off more than a few years of fuel injection practical experience and repair.

There are two throttle chambers (left and right). They are connected by linkage and therefore need to be syncronized similar to a carb sync on our carburated models.

The throttle plates need to be clean. Over the years, carbon and deposits have a tendancy to gum up the plates and shafts, causing the throttle to stick on initial opening as well as keeping the plates from closing completely. Since there are two throttle chambers and only one throttle position sensor, it's important that the chambers be cleaned and balanced prior to setting the TPS.
The TPS adjustment can be accomplished with the engine at rest (not running). Ignition on. #-O
Don't be concerned with the ohm readings from the sensor. The control unit doesn't care about ohms. It sends a voltage signal out to the TPS and is looking for a return voltage. Not resistance. The best way to set the TPS is to monitor the return voltage at the control unit. Most of the time, measuring at the TPS is the same, depending on the condition of the return wire.
Most EFI, CFI, LMNOP (whatever term you're most comfortable with) systems use a five volt reference value to the sensor. Return voltage at closed idle is generally set at between .45-.48 volts. As the throttle opening increases, the voltage should rise to around 4.2-4.5 volts.
The TPS is just a resistor. As the opening changes, the resistance changes. Since the voltage increases, it's pretty safe to say that the resistance decreases. Since you're showing less resistance than called for, it's a good bet the throttle plate(s) is open too far.

Clean your throttle plates. Balance your throttle chambers. Set your TPS to .45 volts and get back to us.

[Guest]

Thanks so much you guys. you RULE! I'll keep fiddlin' 'till I figure it out, which I could never do without this forum. I'll keep ya posted.
Thanks again,
Les

[Guest]

Hello Mr. Glhonda.
First I want to thank you for your in depth reply.
I went out this morning and did the throttle plate clean as per your instructions. Put some more Seafoam in the tank warmed her up and synchronized the throttle bodies with my home made manometer. Got 'em right on the money @1000 rpm.

Went for a test. Same problem. the bike has plenty of power when the engine is under load. As soon as you take the load off and then twist the thottle slightly open again she hesitates and bucks but just a little more throttle and she smooths right out again. Bike was warmed up when I did the sync. as soon as I drive it go through a few gears and come to a stop, she wont idle. Using an inordinate amount of fuel, and the last time I checked the plugs have black powdery carbon deposits on them. It cleans right off.

I'm also not sure where I measure the .45v TPS return voltage. The test I did was unplug the TPS and putting the probes into the connector comming FROM the TPS and having the meter set to OHMS, the needle on the analog meter arced, or appeared to me to arc smoothly.

I'm not giving up, but any help along the way is GREATLY appreciated.
Thanks,
Les

[Guest]

If you trace the three wires from the throttle switch back to the control unit, you'll find that pin number 3 is a ground. (G/Bu)
Pin number 29 (R/W) is the 5 volt reference voltage the control unit is sending out, and pin number 11 (eleven) is the return voltage. (Lg)
Loosen the screws that fix the throttle position switch. With the connector plugged in, and the ignition on, back probe the center wire (Lg) with a votlmeter and adjust the throttle switch until a reading of .45 volts is achieved.
If the adjustment starts out too high, you'll know where your fuel consumption problem is coming from.

[Guest]

Way cool Gl! I'm just somewhat reluctant to dig into those break-off bolts. But I'll dig into the computer tomorrow if I have a chance.
Thank you for your time.
Les

[Guest]

Hey Gl,
Thanks for the help. I'm new to the forum so I'm still awkward with the protocol. I think I understand 'cause I get frustrated when I'm reading the archives, and the thread ends before the original posters question has been resolved. I started assuming that the members were communicating privately. But when I PM'd you I thought I'd paste it so any one in the future could read both the query and the reply.

Anyway, thanks again,
Les

[roscoepc]

Sometimes the original poster just doesn't get back with the result's... I allway's figure that the bike is repaired and they are too busy riding to post!! :mrgreen:

[Guest]

The spark plugs should not have any color to them. When you checked your fuel pressure did you check to see if it held fuel pressure after you turned off the bike. If it did not hold pressure then the fuel injectors could be leaking extra fuel into the engine. There are manifold pressure sensors on this engine. If the vacuum line to the sesors are disconnected or if the sensors are bad it can cause the problem that you are having. Have you checked the led lights on the injection control computer? If any of those lights are on there is something wrong. Fixing that problem should be the solution to your problems. If you do not have a repair manual you could post which lights are on and I can tell you the trouble code.

[Calif Wingnut]

<!-- m --><a class="postlink" href="https://docs.google.com/viewer?a=v&pid=gmail&attid=0.1&thid=131bacf176295f2a&mt=application/pdf&url=https://mail.google.com/mail/?ui%3D2%26ik%3Dfc8c73e636%26view%3Datt%26th%3D131bacf176295f2a%26attid%3D0.1%26disp%3Dsafe%26zw&sig=AHIEtbTHfxQIMPHQ5-VcBScboX2Hq4y1zQ&pli=1">https://docs.google.com/viewer?a=v&pid= ... y1zQ&pli=1</a><!-- m -->