GPZ1100 with Old-Styl DFI Won't Start When Hot

Have looked at fuel pressure? Connect a gauge tee into the pump output to fuel rail.
Could be leaking fuel injectors, causing flooding. Check the plugs to see if they look wet.
Check the spark quality, voltage to coils etc. Mfolks has the above for pick-up coils.
If the plugs look dry, does it fire with a quick shot of ether?

GPZ1100_Rider wrote: Guys:

Worked on it tonight, and here's what I did, and what happened:

Checked the engine temperature sensor and air flow meter per the factory service manual's specs, and everything checked out. I have a spare of each that I picked up over the winter and checked those too. They were within the factory resistance check specs also, so for the heck of it, I swapped those with the originals that came on the bike just in case. Mounting hole threads, cylinder head mounting surface, and connections for the engine temperature sensor were clean and tight.

I fired the bike up and rode it at high speed (70 - 80 MPH) for 40 miles straight with no problems, came home (I'm right off the highway) and shut it off. I tried to start it immediately, and it started fine and ran, but after 10-15 minutes, it would crank and not fire up. After 37 minutes, it started and ran, but I didn't take it for a ride. It revved in the driveway all right though.

The temperature tonight was around 85F.

I checked the valve clearances last fall, and they were all right, and I haven't put much more than 600 miles on it so far this year.

I owned one these same GPZ's many years ago, and I cannot recall it acting like this when the temperature was in the eighties, back in the eighties.

Would it be a good idea to take a hair dryer or heat gun to suggested electrical items to see if they'll act up when heated with either? As I had said earlier, I have replaced the complete ignition with Dynatek components (Dyna III ignition, Dyna green coils and Dyna wires, and NGK plugs).

Could a tight valve or two, really throw off the DFI system this much, and have it exhibit this type of behavior? I hate to go back in there to check them again, but again, I picked up a pair of '83-'84 GPZ cams that I could put in during the effort. I also have a newer Walbro fuel pump and Bosch adjustable fuel pressure regulator that could be thrown in for good measure. However, I was looking to do some or all of that after this riding season.

I'm open to suggestions for checking other things.

Thanks again.
Marty

Marty,

So we now know it only happens when it's heat soaked. I lean away from ignition being the problem [obviously because you installed new Dyna already] but not totally rule it out. It's simple enough to repeat what you just did and yank the plug wires off to see if it's got spark. You don't need to pull the plugs if you have some spares to pop in the plug caps.

If it has spark, remove the return fuel line from the tank. That will bleed off pressure. Reconnect the line and see if the bike will start.

If it has no spark, remove the ignition cover. Let the bike cool down, then ride it again with the cover left off.....see what happens then. Solution at that point would be obvious.

Fuel pressure should be 33 PSI at idle, on my bike it goes up to 35 PSi as soon as the TPS moves. Fuel pumps do wear out & need replacement:

Fuel Pumps & Regulators
www.fuel-pumps.net/gsl393.html
www.mpsracing.com/products/MPS/FuelPumps.asp

Hey:

Thanks for the fast replies. Mike thanks for the tips on looking at the iginition components, but I feel that's covered with the new, full-Dyna system that I installed last fall. But, new parts can be bad out of the box, or fail quickly sometimes.

Motor Head, right before this riding season, I sent my injectors to WitchHunter performance and they went through those thoroughly, so I think I'm covered there too.

Last fall I checked the fuel pressure and found it to be spot-on per the Factory Service Manual for the pressures at and off-idle, but that was last fall.

I'll do a repeat of the ride tomorrow night, then pull the spark plug wires and check for spark, and do the pressure regulator bleed too. Then, if required, I'll pull the points, oops, ignition cover, and run it without it in place to see what happens. Will probably see if the plugs are soaked with fuel too.

Will report back after all of that.

Thanks again to all for the fast responses.

Marty

With a gauge installed, you can block off the lines and see if the injectors leak down.
Also there is a check valve in the pump that should hold pressure. If it bleeds right away I would say bad check valve.
Also checking the resistance of the temp sensor at the Computer main plug would be a good idea. As any exta resistance would change the fuel mix.

The one way fuel return valve in the bottom of the tank on the right side may also be acting up. If it's sticking, the bike will run rich. I've seen them at I believe, www.redlinecycle or www.americanclassix.com

I'm wondering if the fuel pump is becoming heat soaked and not putting out optimum "hot" pressure ?

This is the exact reason I have 3 complete spare, working DFI setups up in my attic ...

When you describe "it won't start hot" is the engine "trying to start" (like a flodded engine) or is it simply cranking and nothing else is happening (like no spark cranking)

Everyone:

I once again took the bike out for a long high speed run averaging 70+ MPH for over 40 miles, and came home and shut it off. I waited 15 minutes, and unlike the last few times, it re-started fine.

Well, here's what I did before I fired it up and went for my ride:

I took off the ignition cover so the Dyna III pickup coils and their mounting plate were exposed. Hmmm.

I also put a fuel pressure gauge between the fuel tank's pressure check valve and the fuel pressure regulator, started and ran it a couple of minutes to see if any pressure was building up at the check valve - no there wasn't.

Ran out of time tonight to throw the ignition cover on it, so I can see if I can repeat the no-start when hot, but I think that should be the next step to confirm that the pickup coils are suffering from heat soak, and causing my problem. If that's the case, I'll take up the problem with whom I bought the Dyna III ignition system from, since I bought it last fall right before the snow started flying, and it hardly has that many hours on it so far this riding season.

I'll report back again after a ride with the ignition cover on.

Still would like any more suggestions and/or insight that anybody may have.

Thanks again for all of the feedback and asseistance.

Marty

I'm not familiar with the mounting configuration of the Dyna ignition coil pick ups, but is it possible to use heatsink compound between the pick up coils and their mounting plate?

You'll need but a thin layer for heat transfer, Radio Shack sells a small tube, more than you'll need. www.articsilver.com is one brand I use on heatsinks.

GPZ1100_Rider wrote: I also put a fuel pressure gauge between the fuel tank's pressure check valve and the fuel pressure regulator, started and ran it a couple of minutes to see if any pressure was building up at the check valve - no there wasn't.

Marty

OK here lies a clue to your problem. The fuel return line check valve acts as a pressure regulator. If the valve is stuck "open", or you have a suspect fuel pump your pump won't be capable of building sufficient pressure.

When I turn on my key, I hear the FP relay kick on, I hear the pump cycle for about 6 seconds then shut off. I also hear fuel flowing back into my tank via the return line.

So its Ignition and not fuel? You lose spark quality or does it go away completely?
Fuel pressure is right, hot and cold, and on restart?
They sell whats called a "Noid" light, to plug onto the injector harness. Shows a flashing light when the signal is there. You can do the same with a test light, back probing the connector. If for some reason you have a coil in the solenoid of the injector shorting intermittently when hot, it would rob the voltage to all 4. Just a thought.
try to pin down as to if it is fuel or spark. Take a spare plug, so then you can just pull off a plug wire and install the spare, lay it on the head and check it.

Hi again:

Won't be able to ride and work on the bike tonight due other committments. However, I'd like to respond to the help that I've gotten again.

Mike, not too sure about the thermal grease on the backs of the pickup coils, but I can investigate that. I think that the best heat transfer would be between the inside of the ignition cover and the tops of the coils. How close they are to each other, and if it's possible to put any thermal pad or something between them I don't know. I have used Chomeric's thermal pads that are like a putty sandwiched between substrates (sticky-backed foil and mesh). I used the stuff for heat sinking a voltage regulator to the frame on my 1997 Honda VFR750, that I sold off. I have been in touch with the business that sold me all of my Dynatek ignition parts, and they seem like they may want to do the right thing, if I can confirm that I indeed have problems with the pickup coils, or another Dynatek component.

Polar_Bus, I think that there's differences between your fuel system and mine. However, I disconnected (per factory service manual) the starter's trigger wire, and cranked the engine. I can clearly here the fuel pump run, build up line pressure, then bleed off excess through the tank's check valve. I would like to check the fuel pressure with my gauge when the motor's hot, but it's a little involved, and I better have a fire extingusher around too.

Motor Head, I have one of those injector do-hickies that I snagged off of Ebay last winter, and used it to confirm good signals to all of my injectors. However, I haven't checked them lately, since this problem has surfaced. I'll check the spark quality after my next test run, maybe tomorrow night.

Thanks again guys. We'll be in touch again, I'm sure.

Marty