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Full Version: 1.7 fuel injected won't keep started when hot
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dknechtly
Guys I'm stumped. My engine was recently rebuilt in the last couple years and I'm working out gremlins. 1.7 fuel injection runs and drives great but when it gets really hot ( I'm in Dallas area), it starts to run erratic. I have to pump the gas or keep it revved high to make it home. When trying to start it. I have to keep pumping the gas to keep it going. I have...
- fuel pressure about 28-29 lbs.
- Bowlsby FI harness maybe 4 years old.
- rebuilt Bolwsby MPS (I've switched out with others) and get no difference
- swapped CPU's; no difference
- swapped coil; no difference
- new 914 rubber HTS; 2200 ohms cold @68 degrees; 118 when hot
- FI points near zero resistance
- no vacuum leaks
- recent valve adjustments (a couple just to make sure)
- fuel pump relocated to front for over 30 years
- pretty new Pertronix ignition (the previous had failed after 10 years)

Any ideas? Thanks


914_teener
I'd swap out the Pertronix for points just to rule it out.

I had a similar problem.

Turned out when it got hot the CHT sensor wasn't completely seated at the connector.

If the ECU doesn't see a ground there the car won't run or intermittent ground it will produce some similar symptoms.


Good luck.
76-914
As Rob mentioned,I'd check the output on the CHT when hot. beerchug.gif
dknechtly
Thanks for the replies. A further update. I found the engine dieseling (run on) after I turned it off. That usually means it is running lean. So, I turned up the knob on the ECU. That seems to have taken care of the hot start issue. I still get a little dieseling so I've added a little more resistance with an inline adjustable resistor. Still a little dieseling. Not sure what to try next. Maybe turn the fuel pressure up another pound?
mgphoto
QUOTE(dknechtly @ Oct 19 2017, 03:13 PM) *

Thanks for the replies. A further update. I found the engine dieseling (run on) after I turned it off. That usually means it is running lean. So, I turned up the knob on the ECU. That seems to have taken care of the hot start issue. I still get a little dieseling so I've added a little more resistance with an inline adjustable resistor. Still a little dieseling. Not sure what to try next. Maybe turn the fuel pressure up another pound?

Run on should not happen with a fuel injected engine as pressure in the fuel ring drops immediately when pump stops and power is cut off to the injectors.
Spoke
You need to check the AFR, then perhaps adjust the MPS. I had to do this when I got my 1.7L going with DJET. At first I added a resistor to the HTS until I realized the MPS needed adjusting.
nordfisch
QUOTE(mgphoto @ Oct 20 2017, 12:07 AM) *

QUOTE(dknechtly @ Oct 19 2017, 03:13 PM) *

Thanks for the replies. A further update. I found the engine dieseling (run on) after I turned it off. That usually means it is running lean. So, I turned up the knob on the ECU. That seems to have taken care of the hot start issue. I still get a little dieseling so I've added a little more resistance with an inline adjustable resistor. Still a little dieseling. Not sure what to try next. Maybe turn the fuel pressure up another pound?

Run on should not happen with a fuel injected engine as pressure in the fuel ring drops immediately when pump stops and power is cut off to the injectors.

Hi,
this is partly correct - and partly false: The fuel line holds most of the pressure for a <very> long time. Pressure gets lost only if the fuel-pressure line is leaking, pressure regulator or check valve are defective or the injectors are dropping.

Check this. Maybe injectors are leaking.

Regards
Norbert
TheCabinetmaker
Check timing?
McMark
Get a wideband O2 sensor to help make the symptoms more apparent. wink.gif
dknechtly
I think I now have it figured out. I was adding resistance to my HTS, but it didn't seem to work in all circumstances. I checked the temp sensor that's under the manifold and got 0 resistance. Since I had no spare, I put in a 220 ohm resistor in between ground and the FI harness lead. Now I have no problem except it takes longer to smooth out on warm up. I guess the CPU wants at least some resistance on it. Now I'll be on the lookout for a spare.
914_teener
QUOTE(dknechtly @ Dec 7 2017, 04:54 PM) *

I think I now have it figured out. I was adding resistance to my HTS, but it didn't seem to work in all circumstances. I checked the temp sensor that's under the manifold and got 0 resistance. Since I had no spare, I put in a 220 ohm resistor in between ground and the FI harness lead. Now I have no problem except it takes longer to smooth out on warm up. I guess the CPU wants at least some resistance on it. Now I'll be on the lookout for a spare.


Cylinder Head Temperature Sensor?

Did you ever check all your electrical comnections when it was hot?

Ever put a wideband to check mixrture?

Your problem sounds like a bad grounding point or connector somewhere.
Garland
QUOTE(The Cabinetmaker @ Oct 23 2017, 08:23 PM) *

Check timing?


Distributor loose shaft.
914_teener
QUOTE(dknechtly @ Dec 7 2017, 04:54 PM) *

I think I now have it figured out. I was adding resistance to my HTS, but it didn't seem to work in all circumstances. I checked the temp sensor that's under the manifold and got 0 resistance. Since I had no spare, I put in a 220 ohm resistor in between ground and the FI harness lead. Now I have no problem except it takes longer to smooth out on warm up. I guess the CPU wants at least some resistance on it. Now I'll be on the lookout for a spare.



If that is the thermotine switch you are talking about it has nothing to do with the ECU.

I simply provides a switched ground to the cold start injector on the plenum if the temperature is below around 40 deg. If you get 0 resistance from the spade to ground then it is bad.

Simply disconnect it. More important are the collected grounds there on the multispades that grounds to the case. Those ground wires have a tendency to crack over time with the heat they are subjected to.
nordfisch
Well done...
Disconnected or broken HTS signals extremely low temperature to the ECU, the engine runs so rich that it dies.

Warming up could be a problem without HTS (but fixed resistor installed), but that's all.

The HTS is still available (here in Germany), it's not so expensive.

Regards

Norbert
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