Need help with hot start issue

polizei · 02-02-2016, 07:58 AM

Guys,

I've been experiencing an escalating hot start issue on my 1987 Carrera. Immediately after the rebuild in 2012, I noticed that I'd need to crank for about 10 seconds to restart the car once the engine got hot. Annoying but I lived with it. Now it's to the point where it won't restart until I let the engine cool down. And if I don't let it cool down enough the RPMs are erratic - blipping high and then nearly cutting out.

I've installed new fuel injectors, and I'm still seeing the same issues. A fellow Pelican installed my DME/chip in his 3.2, and it ran fine. Though it's possible that his car didn't get hot enough to replicate the issue.

I'd really appreciate your guidance on what to check out next. I'm a total ignoramus with troubleshooting electrical issues, so I may end up taking the car in for service, but I figured I'd start here for help.

Thanks guys!

Bob Kontak · Bob Kontak's Garage

If it cools down completely, will the car run fine after it restarts if you don't shut it down?

polizei · 02-02-2016, 08:15 AM

Yes, it will restart and appears to run fine after letting it cool down completely.

patz · 02-02-2016, 08:22 AM

Residual fuel pressure issue. If you get stuck, a shot of ether into the intake will get you going. In my 3.0 it was a check valve in the fuel pump neck that failed.

polizei · 02-02-2016, 08:43 AM

Quote:

Originally Posted by patz

Residual fuel pressure issue. If you get stuck, a shot of ether into the intake will get you going. In my 3.0 it was a check valve in the fuel pump neck that failed.

Thanks Patz. Just to clarify, typically the engine runs fine after letting the car completely cool down. However, I just recalled that during my last DE event I experienced erratic RPMs at the end of a cool down lap followed by the engine cutting out. The engine would not restart until after I let it cool down further. Since then, I've only experienced the erratic RPMs after restarting the engine before it's completely cooled.

Do you still think fuel pump/check valve?

thanks!

patz · 02-02-2016, 08:45 AM

Yes, at least on my CIS 3.0. Hot start only.

Lake Guy · Lake Guy's Garage

I was just reading in the Bently this am about checking fuel system problems and based on that I'd guess check valve issues like Patz suggests. I'd read that section closely and do the tests. Looks pretty straight forward.

patz · 02-02-2016, 07:26 PM

What's nice is the valve is cheap.

polizei · 02-03-2016, 05:18 AM

Thanks guys, I ordered a new one from Pelican and should have it installed next week.

I also read that cleaning the idle control valve can help with the surging conditions I'm experiencing when I restart the car before it's completely cooled. Do you think it's worth it while I wait for the part? And if so, any recommendations on how to clean it? Thanks!

universeman · universeman's Garage

I have heard that ICV can get stuck/dirty and is easy to remove and clean. Search forums. I don't have an ICV on my 3.0 but a friend said that cleaning his stopped the wandering idle.

Porsche 2 · 02-03-2016, 07:21 AM

I had the same problem with my '87 32.2. Replacing both flywheel sensors (probably the originals) fixed this problem.

kmoush · kmoush's Garage

STOP!

Okay I just fixed the same problem on my 86 Carrera this past weekend. My situation is the same as yours. Here is what I recommend to avoid spending money unnecessarily.

FIRST - If you do not have a Bentley manual GET ONE. Otherwise don't embark on the DIY trouble shooting efforts and "walk in the dark". It will cost you.

SECOND - Do not start just replacing things, ......again shooting in the dark.

Now, let me give some background on my situation.

My car would start fine when cold. If brought it to temp and turned off, car would not start after letting it sit 5-10 minutes. I had to wait at least an 30 min, sometimes an hour, to cool before it would start. Car would then start and run fine.

So, as people mention it is the fuel pump check valve, or the fuel press reg. I went ahead and replaced the check valve since I had the car on a lift and with 167,000 miles replaced it as PM and since access to a lift is limited. This did not solve the problem. People also say to replace the fuel reg. But don't......yet.

Next, I purchased a Fluke multi meter and temp sensor and checked resistance of the CHT sensor, at ambient temperature (was within range per Bentley Manual). However at operating temperature I had sporadic/inconsistent readings. To check this disconnect the CHT Sensor plug located on the 3 plug cluster located between the fuel filter and passenger compartment hot air blower. Several posts related to CHT sensor replacement show pics of this plug. BUT refer to Bentley manual.....which you have purchased. NOTE when you disconnect the plug, gently remove the wire retaining clip from the female plug. This will make the next troubleshooting steps easier to do. AND be careful not to let it drop into the engine well. Trust me.

NEXT, go to Radio Shack and purchase a 330 OHM resistor (5 pack) for $1.49. The reason for this is that I read several posts where people get erroneous readings from the sensor at operating temp. So I wanted to be sure, and at $1.49 that is worth it.

NOW this is important. Reconnect the CHT plug (retainer clip removed) to the CHT. Make sure the engine is cool to the point where you have been able to get it to start in the past. Start the car and let it get to temperature. Shut the car off. Let the car sit 5 maybe 10 min? Long enough to replicate the "hot no start issue". When the car will not start, disconnect the CHT and jumper the female side of the CHT plug with one resistor. Now try and start the car. If it starts fine. Shut it off, remove the resistor and then and plug the CHT back in, and try starting again. Does it start? If not insert the resistor once again and see if it starts. If it does then you need a new CHT sensor. Wayne has a technical article on how to replace it. If it does not start use refer to the Bentley manual, start with the "Fuel Injection" section. But I bet the car will start.

Don't take this personally, but your comment "I'm a total ignoramus with troubleshooting electrical issues" can be eliminated by purchasing the Bentley manual, and purchasing the proper tools. I spent $110 on the Fluke meter and a fuel pressure test gauge kit allowing me to trouble shoot this issue properly and very easily. In total with the CHT Sensor and tools, I spent $200.00. I know I will need these tools again, and have avoided replacing parts that did not need to be replaced.

Good luck and let us know how it went.

kmoush · kmoush's Garage

Quote:

Originally Posted by polizei

Thanks guys, I ordered a new one from Pelican and should have it installed next week.

I also read that cleaning the idle control valve can help with the surging conditions I'm experiencing when I restart the car before it's completely cooled. Do you think it's worth it while I wait for the part? And if so, any recommendations on how to clean it? Thanks!

I had the same surging issue you speak of, the new CHT fixed that.

kmoush · kmoush's Garage

STOP!

Okay I just fixed the same problem on my 86 Carrera this past weekend. My situation is the same as yours. Here is what I recommend to avoid spending money unnecessarily.

FIRST - If you do not have a Bentley manual GET ONE. Otherwise don't embark on the DIY trouble shooting efforts and "walk in the dark". It will cost you.

SECOND - Do not start just replacing things, ......again shooting in the dark.

Now, let me give some background on my situation.

My car would start fine when cold. If brought it to temp and turned off, car would not start after letting it sit 5-10 minutes. I had to wait at least an 30 min, sometimes an hour, to cool before it would start. Car would then start and run fine.

So, as people mention it is the fuel pump check valve, or the fuel press reg. I went ahead and replaced the check valve since I had the car on a lift and with 167,000 miles replaced it as PM and since access to a lift is limited. This did not solve the problem. People also say to replace the fuel reg. But don't......yet.

Next, I purchased a Fluke multi meter and temp sensor and checked resistance of the CHT sensor, at ambient temperature (was within range per Bentley Manual). However at operating temperature I had sporadic/inconsistent readings. To check this disconnect the CHT Sensor plug located on the 3 plug cluster located between the fuel filter and passenger compartment hot air blower. Several posts related to CHT sensor replacement show pics of this plug. BUT refer to Bentley manual.....which you have purchased. NOTE when you disconnect the plug, gently remove the wire retaining clip from the female plug. This will make the next troubleshooting steps easier to do. AND be careful not to let it drop into the engine well. Trust me.

NEXT, go to Radio Shack and purchase a 330 OHM resistor (5 pack) for $1.49. The reason for this is that I read several posts where people get erroneous readings from the sensor at operating temp. So I wanted to be sure, and at $1.49 that is worth it.

NOW this is important. Reconnect the CHT plug (retainer clip removed) to the CHT. Make sure the engine is cool to the point where you have been able to get it to start in the past. Start the car and let it get to temperature. Shut the car off. Let the car sit 5 maybe 10 min? Long enough to replicate the "hot no start issue". When the car will not start, disconnect the CHT and jumper the female side of the CHT plug with one resistor. Now try and start the car. If it starts fine. Shut it off, remove the resistor and then and plug the CHT back in, and try starting again. Does it start? If not insert the resistor once again and see if it starts. If it does then you need a new CHT sensor. Wayne has a technical article on how to replace it. If it does not start use refer to the Bentley manual, start with the "Fuel Injection" section. But I bet the car will start.

Don't take this personally, but your comment "I'm a total ignoramus with troubleshooting electrical issues" can be eliminated by purchasing the Bentley manual, and purchasing the proper tools. I spent $110 on the Fluke meter and a fuel pressure test gauge kit allowing me to trouble shoot this issue properly and very easily. In total with the CHT Sensor and tools, I spent $200.00. I know I will need these tools again, and have avoided replacing parts that did not need to be replaced.

Good luck and let us know how it went.

scarceller · scarceller's Garage

A no start can be missing fuel or spark or both. So let's start with spark first:

Remove the center spark wire from the dizzy and put a test plug directly onto that wire, you want the test plug connected directly to the coil. Then, with vise grips clamp the plug to the main ground screw on intake runner #1. Have someone crank the engine, do you have spark?

If you have spark we move to fuel: put a Fuel Pressure gauge on the fuel test port on the LHS (drivers) fuel rail, then in the front trunk jumper 12 volts to the fuel pump fuse. Do you hear the pump? and do you have 34-36 PSI at the rail?

Do those tests and report back.

I suspect faulty ref or speed sensors, but one step at a time. If these sensors are the issue you won't have spark, so test for spark when hot and no start condition occurs. The sensors sometimes become intermittent with heat, the wire harness from the sensor often is deteriorated real bad from the heat that hits the harness from the heat exchanger. You can see these harnesses if you remove the rear drivers tire and look above the half shaft at the rear of the motor. You'll see 2 black harnesses (speed and ref) along with a white harness (CHT) if they are falling apart you need to replace those sensors. But don't replace anything yet, first do the outlined tests above.