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missing engine rpm signal[200/87] posted by Neal on
Saturday, 10 July 1999, at 6:27 p.m.
I'm troubleshooting a problem on my 87 240DL. It's got a b230f w/auto trans, LH2.2 FI, and volvo/chrysler ignition. While going through the FI ecu tests, the Bentley manual says that with the ignition on, there should be 12V at pin 1. My meter shows about .04v. The connection to that pin is the "engine rpm signal". Following the schematics, I traced it back to pin 8 of the ignition ecu. I checked for continuity between pin 8 of the ignition ecu and pin 1 of the FI ecu and there is continuity. I also checked for 12v at pin 8 of the ignition ecu. No voltage there either. The car starts and runs, but after it warms up and has been idling a while, the car wants to die during acceleration, and when it finally does kick in, the acceleration surges.
So here's my questions:
1. Is the 12v really supposed to be there? I know that manuals can be wrong, and I'd really hate to be chasing my tail if this is a misprint.
2. Months ago while tracking down another problem, I disconnected the igntion ecu connector from the ecu. Today I read in the manual that you shouldn't disconnect the ignition ecu connector, and that if you do, you have to replace the ignition harness because of some "one time only" type of pins on that connector. Is this true? And if it is, who's the bonehead that thought that one up?
3. I was also checking the primary resistance of my coil. The manual states that it should be between 1.1 and 1.3 ohms. Mine reads 1.7. Is this too far out of spec?
Sorry for being so long winded, and thanks in advance for any help.
--Neal
Re: missing engine rpm signal[200/87] posted by abe crombie on
Sunday, 11 July 1999, at 1:15 a.m.
That is a digital signal that is fed to pin 1 of LH ecu. The initial voltage is not critical, only whether it has a pulse while cranking or running. If you check this from back of connector while it is plugged to LH ecu and crank engine over you should see 5-7 volts. I believe you would see the 12V if you switched on key while reading Voltmeter.
If this signal was missing the engine would shut down, not merely hesitate.
The ignition control unit connector is of a type that isn't meant to be plugged/unplugged but it can be functional as long as the connectors make good contact.
The problem you describe can be a faulty coolant sensor, faulty oxygen sensor, faulty air mass meter, or faulty hose between the air mass meter and throttle housing (other things as well). Have you checked the air cleaner housing thermostat?
When you are checking the coil resistance what is the ohm reading on your meter when you just touch the two meter leads to each other? This needs to be subtracted from the reading you get when you are reading between the terminals of coil. For many meters the leads will have .2-.5 ohm when doing this check.
The reading will be as much as 1 ohm higher when coil is hot.
Re: missing engine rpm signal[200/87] posted by Neal on
Sunday, 11 July 1999, at 9:21 a.m.
Thanks for replying Abe. I checked the coolant sensor during the FI ecu tests. The resistance reading I got matched the graph in the manual (correct resistance for about 160 degrees F). The oxygen sensor was just replaced. It was definitely not working. The hose between the AMM and the throttle body was also just replaced. It had a hole in it from rubbing against the strut tower. The air cleaner thermostat wasn't working when I got the car about a year ago, and I replaced it.
The meter resistance is .01 ohms when the leads are touched together, but the car had been running about 15 minutes before I did the coil resistance check so that may explain the higher resistance value.
In your experience, is the resistance reading of the AMM that critical? The manual states that the resistance (I think between pins 2 and 6) of the AMM should be between 3.5 and 4 ohms. Mine is 3.0 ohms. Would this be enough of a variance to cause the types of problem I'm experiencing?
Thanks again. You saved me a lot of time.
--Neal
Re: missing engine rpm signal[200/87] posted by abe crombie on
Sunday, 11 July 1999, at 10:39 a.m.
The resistance test for an AMM is more to verify that it is at least continuous inside. The way it operates the resitance test will not allow you to really verify whether it is working properly.
With eng running, fully warmed up, a/c off , out of gear what is the voltage signal out of AMM?
Drive car and get it to act up and then unplug the signal wire from oxygen sensor and see if that makes it better.
Have you checked for presence of gasoline in the hose from the end of fuel pressure regulator to intake maifold?
Re: missing engine rpm signal[200/87] posted by Neal on
Sunday, 11 July 1999, at 11:48 a.m.
I'm not sure where I should check the voltage signal you mention. The only voltage tests listed are the AMM power supply voltage at pin 5 of the AMM and the burn off function test. I've done the burn off function test and that passed. Is there another test not listed?
I'm guessing that the hose you mention for the fuel pressure regulator is the vacuum line from the intake manifold to the regulator. There is no gas in that line. If there was, it would indicate a ruptured or punctured diaphragm, right?
I won't be able to get back to working on the car until later this afternoon, but I'll run that oxygen sensor test then.
I'm also wondering about the possibility of a clogged cat. I know the previous owner drove the car only short distances, add to that the fact that the oxygen sensor was bad, and I'm thinking that I'm a candidate for cat problems. The car has no problem on the highway, though.
Thanks Abe, you sure do make life easier.
--Neal
Re: missing engine rpm signal[200/87] posted by abe crombie on
Sunday, 11 July 1999, at 5:50 p.m.
I don't recall the pins for the AMM but the functions are: 2 grounds, 1 power in, 1 burn off feed, 1 signal out from CO adjustment potentiometer, and the mass signal. I think, this is really a guess, that the signal out is pin 3 at AMM. I believe it is red/white wire.
Yes, the hose having fuel in would indiacte a leaking diaphragm and that could cause surge.
Re: missing engine rpm signal[200/87] posted by Neal on
Sunday, 11 July 1999, at 8:14 p.m.
I'm back. Went out and checked the readings on the AMM.
Pin 1. 0v (GND)
Pin 2. 1.98v
Pin 3. 2.01v
Pin 4. .03v
Pin 5. 13.64v (PWR)
Pin 6. 1.97v
Since pin 1 is gnd, 5 is power, 4 is the burnoff test lead, that leaves 2,3 and 6. The wire resistance test is done between 2 and 3, and the idle mixture pot check is done on 2 and 6, so I'm not sure which of these 3 has the signal, but it sounds like 3 is the correct lead to test. 3 is the red/white wire. In any event, 2,3, and 6 have pretty near the same voltage anyway.
I got the car to the point of acting up (wasn't hard, just let it idle for about 5 minutes) and pulled the oxygen sensor wire. It ran even worse.
Before I started the car, I rechecked the coil primary resistance. At ambient temperature, it's still 1.7 ohms. Resistance read when the meter leads are touched together is .01 ohms, so the lead resistance of the meter doesn't even enter into the equation.
I really appreciate your time. Thanks.
--
Neal
Re: missing engine rpm signal[200/87] posted by Rich K. on
Sunday, 11 July 1999, at 7:05 p.m.
Neal,
Can't help out a lot with the older cars, but I know in the shop one of the first things we look at when a speed sensor is suspected is the cable, to see if it has a yellow stripe on it if so that is the old style speed sensor and has been superceded whith one that has a white stripe on it. Just follow the wire down from where it connects at the fire wall and you'll come across a stripe of some kind.
--Rich K.