740 won't start
Re: 740 wan't start
I have forgotten to inform. At acceleration, the engine types to 1000, and then cut out ( also with disconnected MAF ).
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Kmaniac in California USA
- Posts: 301
- Joined: 15 January 2005
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- Location: Concord, California USA
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Hi there, DVPV:
You have given me a challenge and put me to work. But I don't mind because it gets me to thinking (a scary thought) and I don't mind using my 740 as a test mule as long as people can learn from it.
Your ignition and fuel computers take input from various devices in order to deliver the proper amount of fuel and properly fire the ignition at the right time. In most cases, whenever an input device is disconnected, the computers will compensate with a default setting that will allow operation of the car in a diminished state so you can get it in for service. Some of these include:
Halls Sensor - This is located in the distributor and tells the computer engine speed and relative TDC, assuming the timing belt is indexed correctly. As long as your engine can run, at least for a little bit, we can assume this is operating correctly.
Temperature Sensor - This is located in the cylinder head and has a two-wire lead. Don't confuse this with the temp gauge sensor that has only one lead. This sensor only comes into play when the outside temperature is below freezing and tells the computer to advance the timing a cold start up until the engine warms up. Probably not your problem.
Throttle Switch - This device is attached to the throttle body. There is a switch inside this device that tells the computer when the throttle is fully closed. Closure of this switch prevents the timing from advancing from base timing. When the throttle is opened, activation of this switch tells the computer the throttle is open and allows for normal ignition timing advance. If you haven't done so already, with the engine off, open your throttle by hand and listen for the audible click of this switch as you start to open the throttle and as you return the throttle to the closed position. If you hear this click, nothing more is needed. If not, disconnect the threaded rod between the bellcrank (where the throttle cable attaches) and the throttle are (on one end of the throttle shaft on the throttle body) and check for the click again. If it clicks this time, adjust the length of the rod so that it will click once reconnected. If it does not click at all with the rod disconnected, you may need to replace this switch.
Air Mass Meter (AMM) - This device measures the mass of the incoming air into the engine and is accurate as long as you don't have any vacuum leaks. Vacuum leaks will allow unmeter air to enter the engine, throwing off the air/fuel mixture under all conditions. I measured the idle RPM of my 740 fully warm and with all inputs connected. I measured 1000 RPM. I then disconnected the AMM and restarted the car. It idled at 850 RPM in this state. If your engine idles at a lower speed with the AMM disconnected, it is probably good. If you see no change in RPM with the AMM connected and disconnected, it is most likely faulty.
Idle Speed Controller (ISC) - This device measures the difference in pressure between the incoming air on one side of the throttle valve and the pressure in the intake manifold plenum. The air flow through this device varies with throttle opening, telling the computers the status of engine load. Maximum air flow passes through this device at closed throttle. There is zero air flow through this device at wide open throttle. There is a rotating armature in this device the varies with air flow. I measured the idle RPM of my 740 fully warm and with all inputs connected. I measured 1000 RPM. I then disconnected the ISC and restarted the car. It idled at 900 RPM in this state. If your engine idles at a lower speed with the ISC disconnected, it is probably good. If you see no change in RPM with the ISC connected and disconnected, it is most likely faulty.
Try testing your AMM and ISC using the methods I described above and let us know what you find. Also check the throttle switch.
One more question: When was the last time the timing belt was replaced and who replaced it? There could be other issues here you may not be aware of and could be contributing to your problem.
Good Luck!
You have given me a challenge and put me to work. But I don't mind because it gets me to thinking (a scary thought) and I don't mind using my 740 as a test mule as long as people can learn from it.
Your ignition and fuel computers take input from various devices in order to deliver the proper amount of fuel and properly fire the ignition at the right time. In most cases, whenever an input device is disconnected, the computers will compensate with a default setting that will allow operation of the car in a diminished state so you can get it in for service. Some of these include:
Halls Sensor - This is located in the distributor and tells the computer engine speed and relative TDC, assuming the timing belt is indexed correctly. As long as your engine can run, at least for a little bit, we can assume this is operating correctly.
Temperature Sensor - This is located in the cylinder head and has a two-wire lead. Don't confuse this with the temp gauge sensor that has only one lead. This sensor only comes into play when the outside temperature is below freezing and tells the computer to advance the timing a cold start up until the engine warms up. Probably not your problem.
Throttle Switch - This device is attached to the throttle body. There is a switch inside this device that tells the computer when the throttle is fully closed. Closure of this switch prevents the timing from advancing from base timing. When the throttle is opened, activation of this switch tells the computer the throttle is open and allows for normal ignition timing advance. If you haven't done so already, with the engine off, open your throttle by hand and listen for the audible click of this switch as you start to open the throttle and as you return the throttle to the closed position. If you hear this click, nothing more is needed. If not, disconnect the threaded rod between the bellcrank (where the throttle cable attaches) and the throttle are (on one end of the throttle shaft on the throttle body) and check for the click again. If it clicks this time, adjust the length of the rod so that it will click once reconnected. If it does not click at all with the rod disconnected, you may need to replace this switch.
Air Mass Meter (AMM) - This device measures the mass of the incoming air into the engine and is accurate as long as you don't have any vacuum leaks. Vacuum leaks will allow unmeter air to enter the engine, throwing off the air/fuel mixture under all conditions. I measured the idle RPM of my 740 fully warm and with all inputs connected. I measured 1000 RPM. I then disconnected the AMM and restarted the car. It idled at 850 RPM in this state. If your engine idles at a lower speed with the AMM disconnected, it is probably good. If you see no change in RPM with the AMM connected and disconnected, it is most likely faulty.
Idle Speed Controller (ISC) - This device measures the difference in pressure between the incoming air on one side of the throttle valve and the pressure in the intake manifold plenum. The air flow through this device varies with throttle opening, telling the computers the status of engine load. Maximum air flow passes through this device at closed throttle. There is zero air flow through this device at wide open throttle. There is a rotating armature in this device the varies with air flow. I measured the idle RPM of my 740 fully warm and with all inputs connected. I measured 1000 RPM. I then disconnected the ISC and restarted the car. It idled at 900 RPM in this state. If your engine idles at a lower speed with the ISC disconnected, it is probably good. If you see no change in RPM with the ISC connected and disconnected, it is most likely faulty.
Try testing your AMM and ISC using the methods I described above and let us know what you find. Also check the throttle switch.
One more question: When was the last time the timing belt was replaced and who replaced it? There could be other issues here you may not be aware of and could be contributing to your problem.
Good Luck!
Chris the "K MANIAC"
1986 740 GLE
(5) 1964 Chrysler 300-K's
1986 740 GLE
(5) 1964 Chrysler 300-K's
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Kmaniac in California USA
- Posts: 301
- Joined: 15 January 2005
- Year and Model:
- Location: Concord, California USA
- Been thanked: 1 time
When you measured the pressure of the fuel pump output, how did you do it?
The proper way to measure fuel pump output alone, is to disconnect the fuel supply line from the fuel rail, then connect a pressure gauge to the open line to measure deadhead pressure output from the pumps.
To test the operation of the pressure regulator, you need to attach a pressure gauge on a T-fitting attached between the fuel supply line and the fuel rail. With the pumps running (engine running), you should have a pressure of 36 psi. If the pressure is higher, either the fuel return line is blocked or the fuel pressure regulator is defective. Make sure the return line is clear and rerun the test. If the pressure is too low, the fuel pressure regulator may be bad. Pinch the fuel return line with pliers. If the fuel pressure goes up, the regulator is definitely bad.
Make sure you run these tests first before you start replacing any parts. It could be that your fuel pressure regulator is bad, causing it to recirculate all the fuel back to the tank and not allowing enough pressure in the fuel rail to deliver enough fuel to fire the engine when the injectors open.
The proper way to measure fuel pump output alone, is to disconnect the fuel supply line from the fuel rail, then connect a pressure gauge to the open line to measure deadhead pressure output from the pumps.
To test the operation of the pressure regulator, you need to attach a pressure gauge on a T-fitting attached between the fuel supply line and the fuel rail. With the pumps running (engine running), you should have a pressure of 36 psi. If the pressure is higher, either the fuel return line is blocked or the fuel pressure regulator is defective. Make sure the return line is clear and rerun the test. If the pressure is too low, the fuel pressure regulator may be bad. Pinch the fuel return line with pliers. If the fuel pressure goes up, the regulator is definitely bad.
Make sure you run these tests first before you start replacing any parts. It could be that your fuel pressure regulator is bad, causing it to recirculate all the fuel back to the tank and not allowing enough pressure in the fuel rail to deliver enough fuel to fire the engine when the injectors open.
Chris the "K MANIAC"
1986 740 GLE
(5) 1964 Chrysler 300-K's
1986 740 GLE
(5) 1964 Chrysler 300-K's
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billofdurham
- MVS Moderator
- Posts: 6507
- Joined: 2 February 2006
- Year and Model: 855, 1995
- Location: Durham, England
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This was something that could have kept everyone guessing for months - not a run of the mill problem.Problem was in the bent fuel hose.
Thank you for the update.
Bill.
Work was good - retirement is better.
1996 850GLT 2.5 20v Estate Manual.
1995 Peugeot Boxer 2.5Tdi Autosleeper.
Previously:
1984 244DL, Manual, Beige.
1987 744GLE, Manual, Green.
1991 960 3.0 24v, Auto, Silver.
1994 940T Wentworth, Auto, Blue.
1996 850GLT 2.5 20v Estate Manual.
1995 Peugeot Boxer 2.5Tdi Autosleeper.
Previously:
1984 244DL, Manual, Beige.
1987 744GLE, Manual, Green.
1991 960 3.0 24v, Auto, Silver.
1994 940T Wentworth, Auto, Blue.
I a problem, and it's not a bent fuel line. So. Saturday night my 740 starts up just fine I park it in the drive and leave it. Monday morning I go to start it and it cranks, but no start. I try a few more times...nothing. I come in a google my problem and that led me here. 
Now here is my prob. I realized that the relay wasn't making any noise, and I didn't hear the fuel pump suck any gas while I turned the key. This car sat for a couple of years. It has been worked on. Driven across country twice and is just now getting close to 70k miles- Awesome!. I replaced the fuel filter, the intank pump and sock-my model does not have two pumps. I even replaced the fuel pump relay. relay now clicks, but no fuel to the rail or filter. I fear that I have wired the new pump wrong-even though I followed the diagram. I will-once again pull the pump out of the tank and check the wiring for continuity-I didn't do that at first, I got distracted. Any advice would be great!
Now here is my prob. I realized that the relay wasn't making any noise, and I didn't hear the fuel pump suck any gas while I turned the key. This car sat for a couple of years. It has been worked on. Driven across country twice and is just now getting close to 70k miles- Awesome!. I replaced the fuel filter, the intank pump and sock-my model does not have two pumps. I even replaced the fuel pump relay. relay now clicks, but no fuel to the rail or filter. I fear that I have wired the new pump wrong-even though I followed the diagram. I will-once again pull the pump out of the tank and check the wiring for continuity-I didn't do that at first, I got distracted. Any advice would be great!-
corydevereau
- Posts: 1
- Joined: 15 October 2013
- Year and Model: 740 gle 1986
- Location: south carolina
1986 740 GLE (non-turbo). Car starts perfectly, after replacement of air mass meter and intake air control, but idle then surges for a moment, then calms down.
Attempt to drive car results in stall if I do not wait for idle to settle. Then car runs fine, with slightly elevated idle.
After stopping vehicle, must crank about 20 revolutions of starter before car starts, then it revs high, settles down, and runs fine again. Any suggestions?
Attempt to drive car results in stall if I do not wait for idle to settle. Then car runs fine, with slightly elevated idle.
After stopping vehicle, must crank about 20 revolutions of starter before car starts, then it revs high, settles down, and runs fine again. Any suggestions?
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