No hot start: '95 Lumina 3.1L

Trying to figure out a quirk with my mom's car. The engine will start up every morning, and run great (smooth, good accels) while we're driving around town, but when the car sits after being shut off warm it frequently won't start. Give the car 20-30 minutes to cool down and it starts up fine. The car has been to the local GM dealer and got worked on for a full day, but they couldn't find a cause. To their credit they only charged us for a fuel filter, which was due for replacement anyway. So now I'm trying to figure out the problem.
I initally thought the problem might be the fuel pump relay or the transistor in the ECM that turns on the relay. I took the car out for an errand to get it warm and then shut it off (under a shade tree in case I had to work on it). After I got back to the car about 20 minutes later I tried to start it. Nothing (it cranks fine, but no fire). I swapped in a relay from my truck and tried it again. No difference. I removed the relay and shorted the fuel pump to battery (eliminating the relay and ECM transistor). No difference. Crap. I was 95% sure this was the issue. I then opened the gas cap in case there was a vacuum or pressure, and it sounded normal. As the car cooled down it would try to start, but quickly die. The way the engine was misfiring sounded like a shortage of fuel, as the misfires weren't sharp like when a spark is randomly missing. I tried to come up with some scenarios where the IAC or MAP sensor is malfunctioning, but I don't think they would cause this particular non-start issue.
I assume the fuel pump is fine, as the engine has plenty of smooth power when I try to accelerate.
I pondered if the issue is the DIS ignition module, but presently rule that out as the engine runs smooth until it is shut off. So far I've had good luck with the engine starting right back up when I shut it off. I've only taken it for two test drives so I don't know if it will always immediately start up again.
It's only failed once while running. My sister was driving it last week down the highway for about a half hour when it died. I wouldn't restart. Once it had cooled down for about an hour it started back up and she drove it back home. I'm now trying to figure out the problem.
I have access to another MAP sensor and DIS module cheaply at my favorite junkyard, but I hate to just throw parts at it without a good technical reason. The temperature thing makes me think there's a solder issue somewhere, but why doesn't the problem show up more often while the car is actually running?
So, if you have any thoughts on what I may be overlooking please let me know. I'm next going to attempt to check for any malf codes if I can.

Thanks,
Mike

Does it have an oil pressure switch? Maybe hot oil is too thin on the old sensor.

I have a Snap-On scan tool available if it might help..

First off, I know nothing of your car there....but in general, if any of the engine control devices is screwed up for any reason, generally that bastard WILL start and run....maybe run like SHIT, but it will run....

IMO, fuel pump/relay/wiring....

had a really rough issue on a Dodge van....Crank position sensor...wide open, still gave enough of a raggedy assed signal to run the van, but that coil got a MEG ohms reading....

Ever since my '78 Datsun 810 wagon, which had a highly intermittent no start problem, I finally caught that bastard pants DOWN, ass out....and it was the wiring to the fuel pump from the FP relay...back on a plug in I soldered the connection on and put RTV on it....drove fine for some years, untill I hauled ~500000000 lbs of concrete behind it...another story....


:amazed:

Is that 3.1 similar to the later 3.8 setup where the ignition module is located under the three coils on top of the driver side exhaust manifold ???

If so, it might be an issue with heat soaking from the hot exhaust into the module - it will get hot as soon as the car stops and no air goes thru the engine bay. You should see problems when idling for a few minutes....

The GM smart guys chose a really awesome location for this module: on top of the header where it gets hot and right under the cowl where it gets wet when the weatherstrip at the hood is leaking.... ask me how I know....LOL

There is an insulator between the module and the support it sits on, is that thing crumbled to dust ???

hook fuel pressure gauge to it and see what it does when it doesn't start. My 97 camaro fuel pump caused the car to do what you are describing and about 4 days later it just died.

But prior it would idle a few minutes then just die, then would take about 15 minutes before it would restart then die again.

Update

Okay, bought a fuel pressure gauge at NAPA and hooked it up to the fuel rail. Cliff note results:

When things are running right the fuel pressure is 36#. The engine runs smooth, and has good power when accelerating on the road.

After the car is driven a while and shut off, frequently the engine won't start again after sitting for a short while. (A longer cooldown period will enable a restart.)

During these failure times the engine will frequently start up (due to residual fuel pressure) and die quickly as it drains the fuel rail of pressure. Problem appears to be that the fuel pump isn't working some times. I eliminated the ECM and FP relay by running a jumper wire from the battery positive terminal to the relay output pin to the fuel pump. No response from the pump. Question: If it's a bad pump why does the engine run just fine (smooth, with good power) when it's running? I put my ohmmeter to the relay output line (the battery feed to the pump) and I get 7-13 ohms depending on which time I measure it. This seems high to me, as I would expect something in the 2-4 ohm range, as I would guess that the pump would use at least 3-5 amps. That's just my guess as I have no actual data information on the pump. So right now I am thinking that either I have a resistive connection in the wiring harness preventing sufficient current flow to the pump, or a resistive connection in the pump. When the harness or pump cools down then the pump seems to work fine.
So, next step is to crawl under the car to see if I can run a parallel (extra) feed line from the battery to the fuel pump positive wire to remove any harness resistance from the equation.

Am I missing anything here?

Thanks,
Mike

I always thought these GM in tank pumps either ran or failed.

Neighbors Jimmy would run great one minute, then crappy, then fine.
Chased it all around. Doug came over, adjusted the idle solenoid, and it ran fine, then boom, crappy again.
He suggested we change the fuel pump. Boom. No problems for a year. Sometimes, they just intermittently fail, and that's it.

My Sunfire used to quit while I was driving at speed after waiting 5 - 10 mins the car would start right up and pull to 5000 rpm, did this about 6 - 8 times over 6 months and then quit for good. replaced the pump from one out of a wreck and it was good for about 2 years before it quit again

69427 said:

Okay, bought a fuel pressure gauge at NAPA and hooked it up to the fuel rail. Cliff note results:

When things are running right the fuel pressure is 36#. The engine runs smooth, and has good power when accelerating on the road.

After the car is driven a while and shut off, frequently the engine won't start again after sitting for a short while. (A longer cooldown period will enable a restart.)

During these failure times the engine will frequently start up (due to residual fuel pressure) and die quickly as it drains the fuel rail of pressure. Problem appears to be that the fuel pump isn't working some times. I eliminated the ECM and FP relay by running a jumper wire from the battery positive terminal to the relay output pin to the fuel pump. No response from the pump. Question: If it's a bad pump why does the engine run just fine (smooth, with good power) when it's running? I put my ohmmeter to the relay output line (the battery feed to the pump) and I get 7-13 ohms depending on which time I measure it. This seems high to me, as I would expect something in the 2-4 ohm range, as I would guess that the pump would use at least 3-5 amps. That's just my guess as I have no actual data information on the pump. So right now I am thinking that either I have a resistive connection in the wiring harness preventing sufficient current flow to the pump, or a resistive connection in the pump. When the harness or pump cools down then the pump seems to work fine.
So, next step is to crawl under the car to see if I can run a parallel (extra) feed line from the battery to the fuel pump positive wire to remove any harness resistance from the equation.

Am I missing anything here?

Thanks,
Mike

Click to expand...

You should be able to connect a power source right to the fuel pump fuse and the pump should run. There is also a oil pressure switch that can cause this "no power" to the fuel pump. Just run a wire from IGN terminal to one side of the fuel pump fuse and see if car runs fine, this will bypass all electronic related issues if it does run fine it isn't the fuel pump.

Like yours two days before mine died it had extended crank to start times and sometimes after started it would just die.

MIKE, the last 3 men, and me agree.....

and yes, I have had flaky pumps too, the symptoms all match up....

edit, add....the nature of failure with any DC motor depends more on the brushes it has to have, vs what we are more used to with running AC power most anywhere else.....Blame the Edison/Westinghouse conflict.....100 years ago....

:flash:

JeffP1167 said:

You should be able to connect a power source right to the fuel pump fuse and the pump should run. I ran a line from the battery positive to the relay output terminal. Nothing happened. I don't have a wiring diagram for this car, but it's my understanding that the relay output terminal supplies the power to the pump. There is also a oil pressure switch that can cause this "no power" to the fuel pump. ???? Just run a wire from IGN terminal to one side of the fuel pump fuse and see if car runs fine, this will bypass all electronic related issues if it does run fine it isn't the fuel pump.

Like yours two days before mine died it had extended crank to start times and sometimes after started it would just die.

Click to expand...

I'm not following you on the oil pressure switch statement. Every car wiring diagram I've seen with the oil pressure switch circuit indicated that the oil pressure switch was a redundant driver for the pump circuit, not an additional item that needs to function to get the fuel system to power up.

69427 said:

JeffP1167 said:

You should be able to connect a power source right to the fuel pump fuse and the pump should run. I ran a line from the battery positive to the relay output terminal. Nothing happened. I don't have a wiring diagram for this car, but it's my understanding that the relay output terminal supplies the power to the pump. There is also a oil pressure switch that can cause this "no power" to the fuel pump. ???? Just run a wire from IGN terminal to one side of the fuel pump fuse and see if car runs fine, this will bypass all electronic related issues if it does run fine it isn't the fuel pump.

Like yours two days before mine died it had extended crank to start times and sometimes after started it would just die.

Click to expand...

I'm not following you on the oil pressure switch statement. Every car wiring diagram I've seen with the oil pressure switch circuit indicated that the oil pressure switch was a redundant driver for the pump circuit, not an additional item that needs to function to get the fuel system to power up.

Click to expand...

Unless it see's 4psi fuel pump no worky ... I had oil contamination on my 90 vette and wonder if this could have affected the switch. It is also doing the same as O/P lumina ... Pump sometimes runs and sometimes doesn't (new pump)

JeffP1167 said:

69427 said:

JeffP1167 said:

You should be able to connect a power source right to the fuel pump fuse and the pump should run. I ran a line from the battery positive to the relay output terminal. Nothing happened. I don't have a wiring diagram for this car, but it's my understanding that the relay output terminal supplies the power to the pump. There is also a oil pressure switch that can cause this "no power" to the fuel pump. ???? Just run a wire from IGN terminal to one side of the fuel pump fuse and see if car runs fine, this will bypass all electronic related issues if it does run fine it isn't the fuel pump.

Like yours two days before mine died it had extended crank to start times and sometimes after started it would just die.

Click to expand...

I'm not following you on the oil pressure switch statement. Every car wiring diagram I've seen with the oil pressure switch circuit indicated that the oil pressure switch was a redundant driver for the pump circuit, not an additional item that needs to function to get the fuel system to power up.

Click to expand...

Unless it see's 4psi fuel pump no worky ... I had oil contamination on my 90 vette and wonder if this could have affected the switch. It is also doing the same as O/P lumina ... Pump sometimes runs and sometimes doesn't (new pump)

Click to expand...

I don't have a wiring diagram of the pump harness circuit to dispute that, but I can get the pump to run without the engine running or cranking the engine. I just run a jumper wire across the pump relay pins and the pump runs. I drained the tank to 1/8 level by jumpering the relay terminals and running a hose between the fuel rail schrader valve and a couple large gas cans.
Now to see how much it's going to cost to get the pump swapped.

Took the car to a local mechanic who was recommended by my cousin. Had him put a new pump in. Car's running well now. My sister is using the car while she's visiting my mom. I got a couple other items running again (the mower and the clothes drier), and then headed back home.

Thanks for all the input, guys.

Sounds like you are the family "Mr. Fit It".

Those in-tank fuel pumps are pretty flaky. I had one go in and out, turned out to be a bad ground.

BBShark said:

Those in-tank fuel pumps are pretty flaky. I had one go in and out, turned out to be a bad ground.

Click to expand...

And they almost NEVER fail with an empty or low fuel level. Nearly always right after you fill up. And then you get to drop the tank to replace it.

TimAT said:

BBShark said:

Those in-tank fuel pumps are pretty flaky. I had one go in and out, turned out to be a bad ground.

Click to expand...

And they almost NEVER fail with an empty or low fuel level. Nearly always right after you fill up. And then you get to drop the tank to replace it.

Click to expand...

I got lucky with my Sunfire, when it went I only had 1/2 tank

Stpman said:

TimAT said:

BBShark said:

Those in-tank fuel pumps are pretty flaky. I had one go in and out, turned out to be a bad ground.

Click to expand...

And they almost NEVER fail with an empty or low fuel level. Nearly always right after you fill up. And then you get to drop the tank to replace it.

Click to expand...

I got lucky with my Sunfire, when it went I only had 1/2 tank

Click to expand...

Which is why I never considered for a second, using a intank pump for my FI conversion....mounted to rear frame cross piece with a wrap of rad hose and a hose clamp....GOD I"m lazy....:hissyfit::gurney:

TimAT said:

BBShark said:

Those in-tank fuel pumps are pretty flaky. I had one go in and out, turned out to be a bad ground.

Click to expand...

And they almost NEVER fail with an empty or low fuel level. Nearly always right after you fill up. And then you get to drop the tank to replace it.

Click to expand...

That's exactly what happened to my sister. She borrowed mom's car to drive (from South Dakota) to a wedding in Nebraska. She filled it up and made it about thirty miles when it died on her. So, before I took it to get a new pump (thankfully the pump was intermittent enough to drive a short distance to the shop) I hooked up a hose to the fuelrail schrader valve and emptied most of the tank into some gas cans I had. I hoped this would make life a little easier for the mechanic.