87 740 turbo intermittent start

Gary Cook · Post by **Gary Cook** » 20 Mar 2004, 09:22

Good spark, good signal to the injectors. Strong gas smell, rich looking exhaust pipe. Cold engine starts normally, hot(20+miles) intermittnet start. If the engine catches the first time then it starts normally, it not then it takes 15-20 of running the starter and partial gas feed, if I'm lucky it starts then. Any ideas?

A.Baker · Post by **A.Baker** » 23 Mar 2004, 09:31

First check the idle speed motor (small,silver,has two hoses. and is the shape of a T.) Block the hoses Co2 cart. work great for this. Start engine.W/ motor pluged in you can watsh operation of motor. Should be smoth. opens with throtle operation closes on RPM desell. Clean w/carb. cleaner. if needed. Next check ECM pins for poor conections.Behind pass. kick panel. Clean as needed. Next there is a sensor for the ECM under the intake between #3and #4 cyl. W/ engine running unplug it. There should be a noticable change in engine operation. if so the sensor may be the cause of your woes. I have done all these things to my 740t as I had a hard too no start concern 10-15 min after start up. The black smoke is an over fuel problem. and W/a faild sensor the ECM thinks the engine is cold and will over fuel the engine.
Good luck let me know if I can help or hinder you.
A. Baker

Volvord · Post by **Volvord** » 23 Mar 2004, 18:46

A.Baker wrote:First check the idle speed motor (small,silver,has two hoses. and is the shape of a T.) Block the hoses Co2 cart. work great for this. Start engine.W/ motor pluged in you can watsh operation of motor. Should be smoth. opens with throtle operation closes on RPM desell. Clean w/carb. cleaner. if needed. Next check ECM pins for poor conections.Behind pass. kick panel. Clean as needed. Next there is a sensor for the ECM under the intake between #3and #4 cyl. W/ engine running unplug it. There should be a noticable change in engine operation. if so the sensor may be the cause of your woes. I have done all these things to my 740t as I had a hard too no start concern 10-15 min after start up. The black smoke is an over fuel problem. and W/a faild sensor the ECM thinks the engine is cold and will over fuel the engine.
Good luck let me know if I can help or hinder you.
A. Baker

A caution with some of these recommondations.

1) be very careful cleaning any ECU contacts, the slightlest staic spark or short will destroy the EMU and it will have to be replaced for many $$$. Whenever an ECU or engine computer is unplugged or plugged in it is advisable that the battery is disconnected.

2) Never unplug or plug in a sensor on a running engine, this can also "fry" the ECU. They are very sensitive to power spikes and open circuits.

Bad connections, poor grounds, dirty injectors, incorrect fuel pressure because of restricted fuel filter or faulty pumps, fuel pressure regulator, can all cause the symptoms you describe. I would also be looking at a stuck or leaking injector as the culprit.

Gary Cook · Post by **Gary Cook** » 23 Mar 2004, 20:38

Thanks for both inputs, to both A. Baker and Volvord, I will try all of your suggestions and let the website. There seems to be more cars out there with very similar problems. Thanks again.

Gary L. Cook
CAMM

Neal Bell · Post by **Neal Bell** » 31 Mar 2004, 19:04

I had a problem almost just like this and tore my hair out for days. Turned out to be a weak coil; when I tested the spark (cold) it looked good but when I ran it for a half hour or so it would start to go out. If this is what is happening to you, beware, it will get worse and you will have to be towed at some point. If you can borrow a coil somewhere and give it a try, it's an easy test.

Gary Cook · Post by **Gary Cook** » 31 Mar 2004, 21:06

Thanks, Neal, believe it or not I did try a new coil (their not cheap) and it worked for a few starts and went back to the old problem. My customer is supposed to return on tuesday and I will see then if the computer's temp sensor ( at the computer) has the correct value. I subscribe to ALLDATA and they have a resistance to temp graph so that I can see if the value is accurate. Thanks for the support

Gary Cook · Post by **Gary Cook** » 03 Apr 2004, 05:20

Thanks for all the inputs. I checked the computers coolant temp sensor and sure enough it had infinite resistance. From 25 years of experience as an aviation electronics tech on naval aircraft, I also tested the continuity of both wires coming out of the sensor and were good. I replaced the sensor, drove the vehicle the perscribed distance and upon return I restarted it 15 times with no problem. My customer was well pleased, thanks again.

Gary Cook
CAMM

cool · Post by **cool** » 08 May 2004, 09:47

The engine crank but won't start.

Volvord · Post by **Volvord** » 08 May 2004, 10:08

"Cool" are you stating a problem with your car in the above post? It would be benificial for a little more information because there are many many reasons an engine will not start. Basically an engine needs compression, fuel, and spark to run.

As a guess from left field I would definitly check to see if your timing belt has broken or skipped.