Hi,

My nephew's (formerly mine) 95 SC2 (M/T, 236k mi) is exhibiting the symptoms described in the title. I drove the car myself yesterday, and it's a bit bizarre.

You'll be driving along on the highway w the rpms at 3200, and in the course of 1 sec, the rpm needle will plunge towards 0, then halfway there it reverses course and you feel a kick as the needle reverses direction.

I've verified that this happens at random RPM and random speed.
He's also been sitting idling or been driving and the engine just completely cut out on him. In one instance, the car would not restart for 5 minutes, but has not downright stalled since.

Or has it?

I assume the RPM dips are momentary stalls caused by either lack of spark or fuel, which come back so quickly that the momentum of the already rotating engine just restarts it. There is no sputtering.

I replaced the CKP (crank pos sens) yesterday (I regularly shotgun parts on my own vehicles) hoping the sensor was beginning to flake out and intermittently kill spark and fuel simultaneously.

Nope.

I do not have a scanner w realtime data capture capabilities though maybe this an excuse to buy one.

I told him to borrow my fuel pressure gauge and snake it betw the hood and windshield, latch the 1st latch on the hood, and drive it around until it happens, then catch a glance at the fuel pressure gauge to see if the fuel pump is stuttering. He has not yet taken me up on it. I also told him that the next time it won't restart, check for fuel pressure or lack thereof at the test port under the hood. Hasn't full stalled but the once.

Checked for F5 issues (it's F5 on 1st gen) ---absolutely immaculate ---but I can't necessarily rule out the connector needing respringing. but if that were the case, all the connectors down there should need it too.....

I considered the ICM but these cars throw ignition related codes like they are on special at Walmart. Then again this is OBD I so actually that's not truly the case here.

Is this the correct approach or am I missing something incredibly obvious?

Orig fuel pump, 236K.

Thanks

 

Ehhhh, just a guess here, derf, but could it possibly be the ignition switch? How many keys is he hanging from it? With a car that age, it wouldn't take that much if the tumblers are worn. Like I said, just a guess.

 

Thank you for the insight sir.

Keep it coming folks, PLEASE.

No extra keys hanging.

Using 3 yr old VIN cut key to replace worn original Saturn key.
Nephew had been using the old key for a few weeks. Did not have issues for many months when using older key, so unless new key has worsened the issues, I'm not sure what to think.

I guess I could perform a differential diagnosis by attaching a fuel pressure gauge and a Voltmeter to a wire corresponding to the ign HOT with key on ONLY (prob will get an analog meter)

Turn the key to ON (record pressure and V)
Start vehicle
Let it run, play with throttle, watch both VM and PSI.

When car hiccups, if it is electrical, the V at the ign will drop, but so will the fuel pressure, since the fuel pump will not have full potential across and therefore not be running at full current and therefore output.


I think the only way to diag the fuel pump is to is to change the fuel filter, and run it until it stalls. If the fuel pump is the issue, the pressure will drop. However, if not an ignition issue, the ign Voltage measurement should not change

Do I have this right?
Any other theories on what could be going on?

 

I would check the ICM, as it sounds like you're losing spark when the engine is stalling out... And a failing ICM can be dying but not throwing codes... My old Ranger done that to me, and it was just out of the blue, no spark... Then, when I arrived an hour later with a towing capable vehicle(glad it was family and not a towing company), she fired right up... It was explained to me that old circuitry can become cracked in such a way that when hot or warm, it can lose connection and spark dies... When it either cools off or connection can be re-established, spark picks back up... That would explain your momentary losses of power..,

Of course, I would also check fuel pressure as this is occurring, as it's possible the fuel filter is plugged shut, or the pump is finally failing... My old Ranger also gave me stalling/sputtering fits due to being fuel starved, and a new fuel filter solved the entire problem...


I guess I clouded the issue more than anything, but nonetheless, that's my 1.5 cents(with wear, tear, and depreciation)

 

no, you added to the mix of possibilities which I need to consider.
As mentioned in last post, I plan to change the fuel filter ( I actually do not know when it was last changed (stares down at floor).

When the car is not doing the intermittent power loss thing, it has brisk, responsive acceleration and displays no symptoms of fuel starvation.

But I understand the heat-related strange behavior of which you speak.

Now that you mention it (I think I noted considering ICM in my 1st post), it MAY make more sense that I am losing (at least) spark vs losing only fuel, since the vehicle does not sputter in the least during these very quick troubled episodes

Changing the CKP proved that it was not the culprit for killing either, But there are other ways to kill spark and other ways to kill fuel.

I'll have to ask my nephew if , when it stalled, it sputtered out (fuel issue) or if it just cut out like someone pulled the plug (electrical--ignition Cyl or ICM).

Thank you for the food for thought.

 

ok,

Luckily my nephew works graveyard shift.
He said it just cuts off (no sputtering).

I will therefore start going through the basic electrical system (batt leads/terminals), grounds, etc, followed by inspection of the ICM--might be a grounding issue..(?) I think I have a spare somewhere in my parts cache for my S cars....grabbed em when I could ....

Hopefully I will find the problem there, as I have no experience troubleshooting ignition cyls or switches, though I suppose a worn contact w some arcing would be a little obvious.

 

I haven't experienced anything like that with my car yet. Then again, I'm not the best source of info on what things do in an engine.

 

that is quite bizzare. The only time I had something remotely similar to that happening is when I first got my truck, the old banks chip would stop communicating with the ecm, going one second, died as soon as you hit the clutch. I would check the ICM too and do the other things you were mentioning, but keep an eye out for a loose connector or wire about to break off. (of course this is me thinking the ICM is what the coils connect to - if it is dont they ground thru the bolts to the body of the trans?) probably not being very helpful of specific, but I will drag out one of the old manuals and look in the troubleshooting section tomorrow. maybe something similar will show

 

it is just such a sudden complete cut out w no sputtering whatsoever. The rpms on the tach plunge sometimes approaching zero on the highway. There is too much road noise to tell if it is stalling and restarting, though now that I think of it ---I should be able to pick that up by watching the idiot lights on the dash.

As much as I want to condemn the 236K old fuel pump, I am yet to catch it in a complete stall/no start condition where I can measure by fuel pressure whether the pump is intermittently going to 0 or something else.

It's not the batt terminals or cables -- i gave them a good tug with no misbehavior from the engine.

I know the coil tests and tolerances. I will have to look up the test procedure for the DIS /ICM module but I do not even feel a miss or get a flashing SES. Or any SES.

I'd really rather this be electrical rather than the fuel pump, given the pain in the **** it is to drop a full tank.

I suppose the key on fuel pressure and idling fuel pressures need to meet spec or either the pump is bad or the regulator is compromised. The regulators and filters were separate back then.

It's just the lack of rhyme or reason as to when and how severely it occurs that is driving me nuts

EDIT: Oh gee, what if the fuel pump relay was defective or loose in its socket and was doing the equivalent of momentarily opening, thus killing fuel to the engine? Then coming right back?

Sounds too simple. Might be true.
In order to cause maximum damage if I forget to unjump it, I could jumper the fuel pressure relay and drive for 400 mi. Should be pretty definitive or leave me stranded somewhere in WV where Bones has told me is inhabited but not under government jurisdiction.

Think simple first.

Sorry, my mind thinks backwards from a solution to look at all the cases that could have lead to that outcome.
This is an extremely valuable approach when you are trying to analyze something backwards towards its origin, but it is often less than optimal when troubleshooting cars. I force myself to do it---old habits are hard to break, especially when working on my own stuff.

I try to keep it real for everyone else's stuff

 

It sure sounds more like an electrical situation than fuel to me, derf. But as you know, I'm not a mechanic. I'd start at the fuel tank and check every connector for a good, clean, tight fit. The relay is a possibility, I guess, but it seems kind of strange to me that it would loosen and then reset itself in the socket. I'm still more inclined to think it's somewhere in the ignition system. But, WTF do I know, right? LOL Anyway, good luck with it as I think this is something that will take you a while to sort out.