3.4L DOHC Dies on the Highway

[scottwhite98]

Need a little help to figure this one out. 

'94 3.4L 122,000 miles. Just had the timing belt replaced.  Happy as a clam, driving down the highway at 55 and it just dies.   Pull over.  It  starts and when the RPM's come down it immediately dies.  Feathering the pedal seems to kill it faster.  Disconnecting sensors didn't seem to change anything. 

No lights that I remember. 

Spark Coils are all delivering spark. 

I remember the old paperclip trick on my '86, but it doesn't seem to work on this '94. Must need some other kind of reader?  

 

Any clues?  

 

Thanks,

Scott W. 

 

[Imp558]

Heat soak is usually a short list of possible causes but rather than just replacing things it may be worth it to talk to a shop that still has a capable OBD-I scan tool and see what's happening when warm.

[scottwhite98]

Not heat soak. Towed it home & let it sit for a few hours. Same behavior. 

 

Let it sit overnight. Still no run.   Security light is off and the Check Engine Light is off. 

 

There must be a system that will get the engine running and then a second system takes over.   Obviously, it's a part that can die without warning, and one that wouldn't set a code, though I have no idea what that would be. 

 

Is there a tool I can purchase to scan this vehicle?  I see that there are jumpers available to connect the older plug to a newer OBDII scan tool.   Anyone have success with those?

 

Thanks,

 

Scott 

Edited September 25, 2018 by scottwhite98
new information

[Schurkey]

16 hours ago, scottwhite98 said:

Is there a tool I can purchase to scan this vehicle?  I see that there are jumpers available to connect the older plug to a newer OBDII scan tool.

There's dozens of OBD 1 scan tools, some new--some used.  I have an ancient Snap-On MTG2500, similar to an MT2500.  You'll need a software cartridge new enough for your vehicle (support for the '2500 ended in 2009, no software newer than that--but '94 should be stupid easy to find.)

 

WHAT IS YOUR FUEL PRESSURE?

[Imp558]

Check the TPS, then the ICM and crank sensor. Those are the common ones after you verify the fuel pressure. 

[scottwhite98]

Picked up a scan tool.  This is data capture at 5 seconds, it registers as running for 2 seconds. 

 

Two things jump out at me.   Quad Driver 1 and 2 are listed as "bad" and the MAF grams/second seems to be way way high. 

 

Another very unusual anomaly...it captured 3 frames of data. In the 3rd, it shows the PRNDL Switch at DRV3, even though I never shifted out of park. 

 

Anything jump out at you folks?

 

Thanks,

 

Scott W. 

[scottwhite98]

Update:   Noting the low battery voltage, I put a charger on it.   I hooked up the scan tool after it had charged and the thing fired right up!    No SES light, but there was a stumble.   It was running, decent, though, not struggling to stay alive.   

 

And then I touched the gas pedal and it immediately died.   Here is the data I recorded right before it quit.  

At first, it shows the Quad Drivers as OK. When the TPS is at 10% just a couple seconds later the Quad Drivers say BAD and it dies. 

[55trucker]

The quad driver control various *output* devices (up to 4 for each driver), seeing a report on a *bad* Quad driver would make me think that the ECM has an internal issue & is failing, but........

 

You mention that you are not seeing a check engine light?

 

your vehicle is a 94, what scan tool are you using to check the system? you're right in that year area where not all scan tools will accurately (bi-directional) scan a GM OBD1.5 system. I'd suggest trying another scan tool that is verified to scan the OBD1.5 system.

 

I also notice that you;re doing the scan in an *open loop* situation, the engine hasn't warmed up to go closed loop.

 

Edited September 27, 2018 by 55trucker

[scottwhite98]

No check engine light. Scanner is an Actron CP9690 Elite.   I have to scroll down and select 1994 Olds Cutlass Supreme and the 3.4L engine in the drop down menu. 

 

 

[Schurkey]

'94 3.4 has a MAF???

My '92 and '93 are speed-density.

[scottwhite98]

4 hours ago, Schurkey said:

'94 3.4 has a MAF???

Apparently  '94 and up do. 

 

[55trucker]

Try to get the engine up to running temp so the fuel system is *closed loop*,

taking readings while still cold & in *open loop* gives you no proper information on what the *controlled devices* are doing as they are not in use while in *open loop* (EGR, EVAP, MAP etc).

The fuel system is running off the default mapping while the engine is cold,

 

I'm seeing in one of your readouts that the spark advance is at *0*, while in the other printout the advance is at *27*, that looks to me like an error with the scanner not getting a proper read on the information. 

[mfewtrail]

3 hours ago, 55trucker said:

Try to get the engine up to running temp so the fuel system is *closed loop*,

taking readings while still cold & in *open loop* gives you no proper information on what the *controlled devices* are doing as they are not in use while in *open loop* (EGR, EVAP, MAP etc).

The fuel system is running off the default mapping while the engine is cold,

 

I'm seeing in one of your readouts that the spark advance is at *0*, while in the other printout the advance is at *27*, that looks to me like an error with the scanner not getting a proper read on the information. 

The MAF reading appears to report actual airflow in closed or open loop on the '94 I have here. That said, his MAF reading is way OFF if there's not some sort of scan tool calculation or translation error going on. Injector pulse width is high as well, particularly that third frame showing it at 64ms.

 

How low was your battery voltage out of curiosity?

 

Despite the scan tool readings, it wouldn't be a bad idea to make sure you have adequate fuel delivery as well(parts stores will rent you a gauge if you don't have access to one. You get your money back upon returning it.)....And maybe re-do your spark test depending on how you tested for spark.

Edited September 28, 2018 by mfewtrail

[55trucker]

1 hour ago, mfewtrail said:

The MAF reading appears to report actual airflow in closed or open loop on the '94 I have here. That said, his MAF reading is way OFF if there's not some sort of scan tool calculation or translation error going on. Injector pulse width is high as well, particularly that third frame showing it at 64ms.

 

 

 

 

Agreed,

 

not knowing the scanner readout characteristics the MAF should read approx 3 grams per sec when at idle, that 3071 might actually be 3.071 but the scanner printout possibly drops the decimal point.

[Imp558]

......... Or it's displaying milligrams.

1g = 1000mg

[mfewtrail]

11 hours ago, 55trucker said:

Agreed,

 

not knowing the scanner readout characteristics the MAF should read approx 3 grams per sec when at idle, that 3071 might actually be 3.071 but the scanner printout possibly drops the decimal point.

That was my initial thought as well, but those flow readings still aren't quite right(even if reported in mg) for the rpm the engine is running unless there's a restriction.  The engine is idling pretty consistently around 1100rpms so the flow rate should be around 8 grams/second at that engine speed, but instead we see 3082, 3071, then 887 despite not much change in rpm over those three frames of data.

 

[55trucker]

6 hours ago, mfewtrail said:

That was my initial thought as well, The engine is idling pretty consistently around 1100rpms so the flow rate should be around 8 grams/second at that engine speed.

 

The engine is at 1100 because the system is in open loop, it would not be that high in a closed loop situation, at a constant 1100 even closed loop suggests that there must be a vacuum leak somewhere.

At this point I would not entirely trust the scanner information (due to the various third party scanners that have difficulty correctly reading the numerous GM OBD1.5 ecm chips of that time), my move would be to use a digital multimeter with hz capability to diagnose the MAF to ensure it is not failing.

 

 

https://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/how-to-test-the-maf-sensor-1

Edited September 29, 2018 by 55trucker

[scottwhite98]

It ran last night when it was dead cold.  I thought about ways to get it to warm up to get it into closed loop so I turned the headlights on... then I hit the A/C button and it died.

 

This morning, I replaced the Throttle Position Sensor and the Mass Air Flow sensor so we can get those out of the way. Same conditions. Starts, won't stay running. Occasionally, it will catch itself and it will rev-up and stay going but mostly it just dies. 

Still no Check Engine light.   If we're not confident this code reader is reading properly, is there any use to posting more data?

 

Thanks,

Scott W.

[55trucker]

Scott:

 

is the check engine lamp actually working?

 

 

the MAF you installed, was a new item or used?

Edited September 29, 2018 by 55trucker

[scottwhite98]

MAF was new.   Bulb is good. 

 

The fuel pressure regulator is under the intake...how do I check to see if it's good?

Edited September 29, 2018 by scottwhite98
new info

[scottwhite98]

Light comes on. Start vehicle, light goes off. 

[mfewtrail]

4 hours ago, 55trucker said:

The engine is at 1100 because the system is in open loop, it would not be that high in a closed loop situation, at a constant 1100 even closed loop suggests that there must be a vacuum leak somewhere.

I realize it's in open loop since it's a cold start, I was just stating the rpm for an airflow vs. rpm comparison.

 

Scott, check this out for fuel pressure regulator and fuel pump testing: https://www.youtube.com/watch?v=peh7-pFycyc 

 

Let us know the results of your maf testing as well. I would suggest not replacing any parts until you have tested them and their wiring, otherwise you're just wasting money on stuff that might not solve your issue.

 

 

[55trucker]

1 hour ago, scottwhite98 said:

MAF was new.   Bulb is good. 

 

The fuel pressure regulator is under the intake...how do I check to see if it's good?

with any other engine one connects a vacuum pump to the vacuum port on the FPR & pulls vacuum to test the diaphragm, then connect a fuel pressure gauge to the scrader valve & test the fuel pressure when the engine is both key on, engine off & engine running.

But this engine's plenum being the design it is one has to pull up the plenum to get access to the FPR vacuum port to do the test AT the FPR, but one can still connect a fuel pressure gauge to the schrader valve located on the over on the front of the engine (behind the PS pump). One can connect a vacuum line to the FPR port at the MAP sensor on the far right side of the plenum & test there but if the plastic line between the two is  worn/ rotted open you won't know if the fault is the FPR itself or the vacuum line seeing as that line is routed under the plenum &  hidden from sight.  

Edited September 29, 2018 by 55trucker

[scottwhite98]

Where is the MAP sensor on this thing?  I've dug all over and can't seem to find it. Right (throttle body side) of the intake?  there are 4 vacuum lines on the back left side.  The one with the steel line that goes under the inspection cover  holds vacuum, as well as the other small hard plastic line.   

 

It must be a fuel pressure issue: I hooked up a new pressure gauge and it is not reading maybe 1-2 psi with the ignition on. (unless the gauge is faulty).   I can't believe it even starts that low. 

[55trucker]

The MAP is at the right rear corner of the plenum (right is the passenger side), 

the plastic tube that connects the FPR to the base of the MAP has a neoprene/rubber connector at each end, after near 25 years it's not unreasonable that those two short rubber connectors would be dry rotted.

 

 

 

Edited September 29, 2018 by 55trucker