88 Cranks no start

[zoltanb]

The 88 that I picked up recently is kicking my butt. I have checked the sensors ,they all check out according to the fsm. I have no spark and no ground to the injectors. I have replaced the ecm from a working car, no change. The ecm has power and ground. the only code coming up is about the cruise not working, the only other thing not working is the light show. The wires under the seats check out with ohm meter and are not wet. The door handle is sending signal when lifted. All the grounds have been cleaned and cooper coated. Fuel pressure is correct. I can make the injectors click from the crank sensor by jumping the pins. Their power hot with the key but they never get ground signal. Could the bcm not be sending data to the ecm? I have also check compression 140 to 145. I do not want to just start throwing parts at it but I really want to see it run. Thank Zoltan

[padgett]

Does the engine turn when you turn the key to start ? Offhand it sound like a bad crank sensor. There is a sequence to go through (on reatta.net) for "Cranks but does not run" that includes a crank sensor test.

Have you ever seen/heard it run ?

BTW has anyone else had the "save" button not work ?

[zoltanb]

Yes the engine cranks and builds compression. No the previous owner said it just died and had to have it towed home.

[Ronnie]

Try David's new procedure for testing the crankshaft position sensor. Check the green fuel pump prime/test connector for 12 volts while cranking the engine over.

If the procedure works as described the green connector will have 12 volts on it as long as the engine is turning if the cps is good.

I believe the test will be more accurate if you disconnect the oil pressure sender before doing the test.

[padgett]

Dunno what the green connector would have to do with the cps. It is live for 2 seconds when you turn the key on (through the relay) and then is on so long as the oil pressure is above 4-6 psi (through the oil pressure sender).

[drtidmore]

Dunno what the green connector would have to do with the cps. It is live for 2 seconds when you turn the key on (through the relay) and then is on so long as the oil pressure is above 4-6 psi (through the oil pressure sender).

It has A LOT to do with the CPS. The CPS is directly read by the ICM (18 pulses per revolution), which outputs a "fuel control signal" pulse every 6 pulses from the CPS (ie one fuel control pulse pulse every 1/3 revolution. This fuel control signal is fed to the ECM. When the ECM sees the Fuel Control Signal, it activates the fuel pump relay which is connected to the green connector as well as the fuel pump.

As I stated in my write up, you need to first turn the ignition to ON and allow the fuel rail priming cycle to complete (ie NO voltage on green connector), then move the key to start. Within 1/3 revolution, if all is well, the fuel pump will be getting 12V which will show up on the green connector. This is WELL BEFORE the oil pressure can begin to rise to the necessary level to override. As Ronnie indicated, you can easily unplug the oil sender as part of this test which isolates the test to verify the CPS regardless of oil pressure. FYI, the oil pressure switch is the BACKUP for the fuel pump relay. The fuel pump relay under the control of the ECM is the PRIMARY control circuit for the fuel pump.

If you don't see 12V on the green connector IMMEDIATELY on starting to crank, then something is wrong and the test only indicates that further troubleshooting is needed.

If 12V DOES come up IMMEDIATELY on starting to crank, that pretty well vindicates the CPS along with the associated ICM and ECM circuits. It does NOT clear the ICM and ECM of OTHER issues which can prevent the car from starting.

Here is FSM schematic of the circuits

David T

Edited September 29, 2013 by drtidmore
MY SCREWUP meant ECM (see edit history)

[Ronnie]

OK, I decided to try and confirm or disprove if using the green fuel pump test connector would be a good way to determine if the crankshaft position sensor was working or not.

When I raised the hood the first thing that I did was disconnect the oil pressure sensor to take the contacts inside it that can sent power to the pump out of the picture. We all know it can send 12 volts to power the pump (and green test connector) so disconnecting the oil pressure sensor will prevent that from happening.

Next, I had to decide how to keep the engine from starting when testing to see if the ECM would send a signal to the fuel pump relay at normal engine cranking speeds. To accomplish that I decided to unplug the fuel pump relay (located on the firewall) and do my testing on the Dark Green wire with the White stripe. It is the wire that comes directly from the ECM to the pickup coil in the fuel pump relay.

Then I connected one lead of my volt meter to ground and the other lead to the fuel pump relay connector, terminal 5, circuit 465, so it was connected to the Dark Green wire with the White stripe.

My battery was a little low from sitting several days. The battery voltage was 12.2 volts.

Here are the results I got when doing my testing.

1. When I first turned the key to the ON position I allowed the brake pump run until it stopped,

2,Then I turned the key off and back again to the ON position, the voltage on my meter went to 11.62 for about 2 second and then slowly dropped.

3. When I turned the key further to the START position, voltage on my meter went to 10.63 and remained constant for as long as the engine was spinning. Although it is one volt less with the starter spinning the engine I'm certain it was enough voltage to pickup the fuel pump relay coil in order to activate the fuel pump.

I tried test 2 and 3 several times to confirm the readings.

4. Next I reconnected the fuel pump relay but left the oil pressure sensor disconnected. The engine started right up and I drove to the end of the street and back. The fuel pump was only powered via the signal from the ECM energizing the fuel pump relay. I did have an error message on the dash about the oil pressure sensor but that was expected with it disconnected. The oil pressure was showing max in the CRT.

5. I reconnected the oil pressure sensor and everything is back to normal after clearing codes.

I realize didn't follow David T's instructions to the letter. I just wanted to do a quick and dirty test to prove the crank sensor is sending a signal to the ECM and I think my testing accomplished that.

David and I have talked about making a ROJ tutorial to test the crank sensor in a similar way to this. I value the opinion of the people on this forum. I would like to hear comments from the rest of you guys about testing the crankshaft position this way.

[padgett]

From 88 FSM page 6C2

[drtidmore]

Per the '89 FSM, page 6C-2.

Could there be difference between how the 88 and 89 actually operate? I seriously doubt it. I can't explain why the 88 FSM states one thing and the 89 states another, but the circuit schematics that I posted pretty well make it clear that that fuel control signal from the ICM is based on the crankshaft sensor (see the pic I posted of the schematic).

David T

[Guest Mc_Reatta]

Problem is the ICM gets in the middle, so can't tell if problem is with crank sensor or with the ICM. But at least confirms it's one of them. ICM is easier to change out, and a recommended spare, so a good one to start with.

[drtidmore]

My suggestion that the green fuel pump connector be used as an analog for a direct test of the crankshaft sensor is that IF it behaves as I and Ronnie have described, the crankshaft sensor IS functioning as are the associated circuits in the ICM and the ECM. It is NOT a exhaustive test of either the ICM or ECM, but simply an easy way to test if the crankshaft sensor can be eliminated as a cause in ONE easy step.

This was never meant to be the end all test. If the green fuel pump connector does NOT show 12V during crank with the oil pressure sensor disconnected, THEN more, deeper troubleshooting is require.

Here is more info on the ICM (known as the C3I module) from the '89 FSM page 6E3-C4-4

This means that using the green fuel pump connector test BOTH of the dual sensors in the crankshaft as the above section states that until it receives BOTH the 18X and the 3X signals from the crankshaft sensor it does NOT output the fuel control signal. Still an even better test than I first thought.

David T

Edited September 30, 2013 by drtidmore
additional '89 FSM info on CPS and ICM/ECM (see edit history)

[padgett]

That is exactly why a few years ago I built a breakout box just for the ignition.

This way I can connect an O'scope or make/break any connection.

[TexasJohn55]

It appears that the 88 FSM has an error concerning the "camshaft sensor" triggering the fuel pump relay. From what I have read on various threads and from actual experience, the 88 3800 will run just fine without a functioning camshaft sensor or magnet with no ill effects or trouble starting.

[padgett]

Could be, testing with a proper rig is the only way to know. Do know that if oil pressure is lost (below 4 psi), the engine will shut down. Have seen sensors that never drop to zero.

[drtidmore]

Could be, testing with a proper rig is the only way to know. Do know that if oil pressure is lost (below 4 psi), the engine will shut down. Have seen sensors that never drop to zero.

Pulling the oil pressure sender connector off makes the ECM believe that the engine has MAX oil pressure (confirmed by Ronnie's test), and pulling that connector off the sensor ensures that the oil sender is NOT powering up the fuel pump circuit. Ronnie's decision to monitor the fuel pump relay COIL voltage rather than the "green" fuel pump connector was do PREVENT the car from starting (ie NO fuel pump relay was connected) as he tested to see if the ECM by way of the ICM by way of the CPS would activate that relay.

As Ronnie noted, not only did the fuel pump relay COIL connection indicate 12V ANYTHING the engine was cranking, once he reconnected the fuel pump relay, the engine started instantly with NO oil pressure sender connected and he drove the car for a short distance to prove to his satisfaction that the ECM/ICM/CPS would power the relay. Again, the oil pressure sender is the BACKUP to the fuel pump relay, not the primary.

Again, from the 89 FSM, it is CLEAR that the crankshaft sensor is the root sensor leading to activation of the fuel pump relay

David T

Edited September 30, 2013 by drtidmore (see edit history)

[Ronnie]

Could be, testing with a proper rig is the only way to know. Do know that if oil pressure is lost (below 4 psi), the engine will shut down. Have seen sensors that never drop to zero.

Pulling the oil pressure sender connector off makes the ECM believe that the engine has MAX oil pressure (confirmed by Ronnie's test)...

These two statements, as well as the fact that Padgett is right 99% of the time, have got me to thinking about the test that I did. I'm wondering if the reason the Fuel Pump Relay coil was being picked up by the ECM was because it was seeing a pulse count from the Crankshaft Position Sensor OR because ti was seeing MAX pressure from the oil pressure sensor.

I wish, as a final part of my testing, I had unplugged the CPS to see if the ECM would still activate the Fuel Pump Relay coil when the engine was spinning. Until someone does that I don't think the testing I did was definitive proof that the ECM powers the fuel pump when it senses pulses from the CPS. The ECM seeing MAX oil pressure could be the reason it was activating the fuel pump relay coil and not because it was sensing pulses from the CPS.

[zoltanb]

Ok I did the test before and after I replaced the crank sensor. Ronnie I can say for fact the with it disconnected and the oil pressure sw connected it still powers the fuel pump. I think it is a valid test and worth the write up. The car now runs great. I still have to figure out the cruise problem.

[drtidmore]

The oil pressure fuel pump switch is a mechanical switch co-housed in the oil pressure transducer housing. It has NOTHING to do with the actual oil pressure transducer. It feeds 12V DIRECTLY to the fuel pump power wire, totally bypassing the fuel pump relay as it is designed to ensure that the fuel pump can be powered should the fuel pump relay fail. (see below from FSM)

I would appreciate a FSM reference regarding a low oil pressure reading causing the engine to cease running. I have read thru all the applicable sections of the 89 FSM and can not find any reference to such being a cause for engine not running and NONE of the schematics indicate that ability. I know it would MAKE SENSE for low oil pressure to be a cause for shutting down the engine, I just don't find it in the FSM.

Here is the oil pressure doc from 89 FSM page 8D2-28. NOTE! that the oil pressure transducer does NOT connect to the ECM, but rather to the BCM.

David T

Edited September 30, 2013 by drtidmore (see edit history)

[padgett]

And you are right, that is how the Buick books read. Now I am going to have to find my 1990 Bonneville FSM because I know I saw the "lose oil pressure and engine dies" somewhere.

[drtidmore]

And you are right, that is how the Buick books read. Now I am going to have to find my 1990 Bonneville FSM because I know I saw the "lose oil pressure and engine dies" somewhere.

Wonder if that was a change they made on the supercharged version of the 3800?

David T

[TexasJohn55]

Something to consider:

Electronic control modules are programmed to switch logic or priorities in the event that a circuit or sensor goes down. When the oil pressure sensor is unplugged, the ECM should recognize this and respond according to however it was programmed. The display of a specific oil pressure reading is simply a default. The question is, what is the programmed logic under those conditions?

I would think that to further troubleshoot and understand which sensor is taking priority, you would need to unplug engine oil pressure sensor and plug the harness into a known good sensor with a regulated air supply and guage to simulate actual engine operating conditions.

Terminology is important also, Fuel Control appears to mean injector fueling control, not Fuel Pump control.

I am very interested to see what you guys figure out on this;

[drtidmore]

Again, the oil pressure transducer is connected to the BCM not the ECM. I have searched for any reference in the FSM to indicate that the BCM communicates ANY oil pressure info to the ECM, but have come up empty handed. Padgett is looking thru his other FSMs as he agrees that Reatta FSM does not support any interaction. From what I can gather and seemingly confirmed by Ronnie, a disconnected oil pressure connector (ie both the transducer and the fuel pump failsafe), has NO impact on the operation of the vehicle. Again, Padgett is looking to see if he can find information that a LOW oil pressure signal could led to an engine shutdown (obviously this would have to be overridden during startup)

As for "Fuel Control" terminology, the FSM uses the term in discussing several processes. Referring back to the various FSM schematics, it is clear is that there is only ONE Fuel Control output from the ICM and only ONE Fuel Control input on the ECM. Yes, the Fuel Control signal is integral the injector operation, but it is also use by the ECM as the signal to switch ON the Fuel Pump Relay as described in the FSM.

David T

[TexasJohn55]

Does an unplugged (open circuit) sensor set a fault code.?

[TexasJohn55]

I used the tern "Electronic Control Module" as a general term for any control module, to include any relevant control module, not just the ECM. My mistake.

[drtidmore]

Each control module handles specific functions. The ECM (Engine Control Module) handles the fuel injection and EGR functionality through a variety of inputs, the BCM (Body Control Module) handles the chassis functionality

While it would seem logical to think that oil pressure would be monitored by the ECM, oil pressure is NOT a variable that impacts fuel deliver or emissions which are the ECM's focus.

Oil pressure is monitored and reported by the BCM, and any action based on such information is purely human. The oil pressure transducer is NOT connected to the ECM. While there is interaction between the ECM and the BCM, such as the alternator functionality and the AC for examples, I can find NO documentation to support that the BCM reports low oil pressure that it is reading back to the ECM for ECM use.

If you pull the oil pressure transducer connector (ie open circuit), you set BCM code B132, NOT an ECM code.

A short in the oil pressure circuit causes a zero oil pressure indication and does not set a specific code of any kind (at least none that I can find in the FSM). It WOULD cause the oil pressure telltale light in the IPC to illuminate as well as low oil pressure message to appear on the CRT. Again, other than the idiot light and the CRT message, low oil pressure is handled with no more weight than low windshield washer fluid.

I know it makes NO sense, as if there really were NO oil pressure, the last thing that you really want is the engine to continue running, but again, it does NOT appear from the FSM that such automated shutdown was part of the Reatta 3800 design and programming.

David T

[Ronnie]

Second and final test:

OK, I did more testing this morning to determine for certain that the ECM picks up the Fuel Pressure Relay coil when it gets a pulsed signal from the Crankshaft Position Sensor. To get up to speed on the previous testing I have done go back and read my earlier post #7 in this thread.

I started my test this morning by connecting my meter as I did in post #7 and then repeated steps 1-5 of my previous test. The results were the same. So that brings me up to where I left off in post #7.

Next, I disconnected the Camshaft Position Sensor to make sure it does not play a part in the ECM picking up the Fuel Pump Relay coil. With the Camshaft Position Sensor disconnected the ECM would still send a signal to the Fuel Pump Relay coil when the engine was spinning at cranking speed.

Next, I did the test I should have done in my last post #7. I disconnected the Crankshaft Position Sensor and then turned the key to the start position to make the engine spin. With the Crankshaft Position Sensor disconnected the ECM DOES NOT send a signal to the Fuel Pump Relay coil when the engine was spinning at cranking speed. I repeated this test several times to be sure I was getting a consistent result.

I feel these final tests prove once and for all the ECM DOES energize the Fuel Pump Relay (which turns on the fuel pump) whenever it receives pulses from the Crankshaft Position Sensor.

I think enough testing has been done that we can mark this theory CONFIRMED!

Now the question is, how do we use this knowledge to come up with a simple test that will help the average Reatta Owner diagnose a problem?

[drtidmore]

Second and final test:

I feel these final tests prove once and for all the ECM DOES energize the Fuel Pump Relay (which turns on the fuel pump) whenever it receives pulses from the Crankshaft Position Sensor.

I think enough testing has been done that we can mark this theory CONFIRMED!

Now the question is, how do we use this knowledge to come up with a simple test that will help the average Reatta Owner diagnose a problem?

Ronnie,

Since the crankshaft sensor tends to fail pretty catastrophically (ie engine won't start, won't run), I think that pulling the oil pressure transducer connector and then monitoring the "green" test lead for 12V is the simplest and most informative test to come out of this effort.

I did not originally advocate the need to pull the oil pressure transducer connection, BUT since the time from crank initiation to the necessary cranking RPMs to build up 4PSI varies, it is probably BEST to eliminate that as a source of 12v at the green wire.

I think that since the goal is to eliminate the CPS as a potential cause of NO start, NO run, there is no need to pull the fuel pump relay plus leaving it connected verifies that the relay is functional (removing yet another potential cause for the no start/run condition).

I think that it needs to be STRESSED that a failure of this test actually proves NOTHING other than the fact that more detailed troubleshooting is required. This test's value is in eliminating a LOT of things that can go wrong with one simple test.

A failure of this test DOES point to where to continue troubleshooting (fuel pump relay, ECM/ICM/CPS and associated wiring) which can be valuable information in the frustration of figuring out why the engine won't start or run.

I just see this test as the FIRST one to perform since it can clear off the table a LOT of things.

Thanks for doing the additional testing. I simply had not had time to get out and do it myself plus it is better that someone else verify what I had been advocating.

David T

[Ronnie]

Instead of using this test as a stand alone test for the CPS I' thinking that I will incorporate it into a tutorial for troubleshooting a "cranks but won't run" condition. I know that the tests are already in the FSM but I would like to simplify them so they can be easily understood by the average Reatta owner who may not understand all the terminology and procedures in the FSM.

It would go something like this:

1. Pull a spark plug wire and test for strong spark. If you have a strong spark you know that the CPS and ICM are functioning well enough to start the engine. If no spark the CPS and ICM should be investigated before moving on to #2.

2. Check the green test connector for 12 volts while the starter is turning the engine. If you have 12 volts at the green connector you know that the CPS, ECM and Fuel Pump Relay are working well enough to activate the fuel pump. If no voltage on the green connector, replace the relay and test again.

3. Test fuel pressure at the fuel rail using instructions already on my website. Correct any problems with fuel pressure and test again.

4. ???

[drtidmore]

2. Pull Oil Pressure Transducer connector(refer to pic). Check the green test connector for 12 volts while the starter is turning the engine. If you have 12 volts at the green connector you know that the CPS, ECM and Fuel Pump Relay are working well enough to activate the fuel pump. If no voltage on the green connector, replace the relay and test again.

That would be my only suggested change to step 2.

Step 4 would depend on whether is more appropriate to start throwing parts or doing deeper troubleshooting.

Step 4 could be to follow your existing CPS troubleshooting process so as to isolate the CPS from the ICM OR it could simply be to replace the ICM as it has a history of failures, especially the 88/89 models (magnavox design).

Step 4 could be to look for the pulsating Fuel Control signal AT the ECM as that would eliminate the wiring between the ECM and the ICM as well as vindicating the ICM and the CPS. This signal pulses 3 times per revolution, so it should be easy enough to watch on a DVM during cranking, no need for an o-scope.

Beyond that, assuming everything is coming up correct, the problem could be in the ECM itself (ie not firing the injectors). An easy test for this would be to run the fuel pressure test and verify that it is HOLDING AFTER the fuel pump power is removed. With the oil pump transducer removed, remove the fuel pump relay and try cranking. If the injectors are firing the pressure will DROP as they fire. Does NOT prove that they are firing at the proper times, which would lead us to the CAM SHAFT Sensor as IT is responsible for syncing the ECM injector firing sequence with the actual engine timing. If the cam shaft sensor has failed, the FSM states that the ECM will randomly initiate an injector firing sequence with a 1 in 6 chance of getting it right. In this scenario the engine would start and run perfectly part of the time (ie ECM guessed correctly), and other times would NOT start.

David T

Edited October 1, 2013 by drtidmore (see edit history)

[89REATTAJIM]

And you are right, that is how the Buick books read. Now I am going to have to find my 1990 Bonneville FSM because I know I saw the "lose oil pressure and engine dies" somewhere.

Hi Padgett.... Unless you had more than one FSM for the Bonne, don't bother looking. You gave us one with the car, I passed it on when we sold the car...... Jim