1.7 fuel injected won't keep started when hot, Runs great cold; won't hardly run when hot |
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1.7 fuel injected won't keep started when hot, Runs great cold; won't hardly run when hot |
dknechtly |
Oct 15 2017, 01:38 PM
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#1
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Yellow 914 Group: Members Posts: 68 Joined: 11-April 03 From: Wylie, TX Member No.: 560 Region Association: None |
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 |
Oct 15 2017, 04:39 PM
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#2
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914 Guru Group: Members Posts: 5,193 Joined: 31-August 08 From: So. Cal Member No.: 9,489 Region Association: Southern California |
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 |
Oct 15 2017, 09:44 PM
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#3
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Repeat Offender & Resident Subaru Antagonist Group: Members Posts: 13,455 Joined: 23-January 09 From: Temecula, CA Member No.: 9,964 Region Association: Southern California |
As Rob mentioned,I'd check the output on the CHT when hot. (IMG:style_emoticons/default/beerchug.gif)
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dknechtly |
Oct 19 2017, 04:13 PM
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#4
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Yellow 914 Group: Members Posts: 68 Joined: 11-April 03 From: Wylie, TX Member No.: 560 Region Association: None |
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?
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mgphoto |
Oct 19 2017, 05:07 PM
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#5
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"If there is a mistake it will find me" Group: Members Posts: 1,330 Joined: 1-April 09 From: Los Angeles, CA Member No.: 10,225 Region Association: Southern California |
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 |
Oct 20 2017, 03:00 PM
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#6
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Jerry Group: Members Posts: 6,964 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
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.
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nordfisch |
Oct 23 2017, 03:38 PM
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#7
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Member Group: Members Posts: 86 Joined: 11-December 15 From: Germany Member No.: 19,451 Region Association: None |
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 |
Oct 23 2017, 07:23 PM
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#8
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I drive my car everyday Group: Members Posts: 8,299 Joined: 8-May 03 From: Tulsa, Ok. Member No.: 666 |
Check timing?
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McMark |
Oct 24 2017, 07:01 AM
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#9
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914 Freak! Group: Retired Admin Posts: 20,177 Joined: 13-March 03 From: Grand Rapids, MI Member No.: 419 Region Association: None |
Get a wideband O2 sensor to help make the symptoms more apparent. (IMG:style_emoticons/default/wink.gif)
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dknechtly |
Dec 7 2017, 06:54 PM
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#10
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Yellow 914 Group: Members Posts: 68 Joined: 11-April 03 From: Wylie, TX Member No.: 560 Region Association: None |
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.
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914_teener |
Dec 7 2017, 08:22 PM
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#11
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914 Guru Group: Members Posts: 5,193 Joined: 31-August 08 From: So. Cal Member No.: 9,489 Region Association: Southern California |
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 |
Dec 7 2017, 09:09 PM
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#12
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Restoration Fanatic Group: Members Posts: 1,325 Joined: 8-January 04 From: ......Michigan...... Member No.: 1,535 Region Association: Upper MidWest |
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914_teener |
Dec 7 2017, 10:30 PM
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#13
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914 Guru Group: Members Posts: 5,193 Joined: 31-August 08 From: So. Cal Member No.: 9,489 Region Association: Southern California |
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 |
Dec 8 2017, 01:29 AM
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#14
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Member Group: Members Posts: 86 Joined: 11-December 15 From: Germany Member No.: 19,451 Region Association: None |
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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