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Posted by: dknechtly Oct 15 2017, 01:38 PM

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

Posted by: 914_teener Oct 15 2017, 04:39 PM

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.

Posted by: 76-914 Oct 15 2017, 09:44 PM

As Rob mentioned,I'd check the output on the CHT when hot.

Posted by: dknechtly Oct 19 2017, 04:13 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?

Posted by: mgphoto Oct 19 2017, 05:07 PM

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.

Posted by: Spoke Oct 20 2017, 03:00 PM

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.

Posted by: nordfisch Oct 23 2017, 03:38 PM

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

Posted by: The Cabinetmaker Oct 23 2017, 07:23 PM

Check timing?

Posted by: McMark Oct 24 2017, 07:01 AM

Get a wideband O2 sensor to help make the symptoms more apparent.

Posted by: dknechtly Dec 7 2017, 06:54 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.

Posted by: 914_teener Dec 7 2017, 08:22 PM

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.

Posted by: Garland Dec 7 2017, 09:09 PM

Distributor loose shaft.

Posted by: 914_teener Dec 7 2017, 10:30 PM

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.

Posted by: nordfisch Dec 8 2017, 01:29 AM

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