Surging and stalling at idle

ericn1300 · 02-07-2011, 08:19 PM

92 Bravada with the vortex engine

The symptom is a tugging and surging from the engine while idling in park and stalling when in gear. The symptoms are less if I keep the RPM high and if I drop it into gear at about 2000 RPM I can get it home ok.

The problem only occurs after a full temp shutdown like when you run to the store and get back in and start it up. I can start it cold and drive it 15 miles or more with no problem but as soon as you shut it down for a few minutes or longer the problem starts again.

I checked the fuel pressure, 62+ cold and no leak down problem after 5 mins. The fuel pump and filter are less than 2 years and 20k. The engine temp is normal. Spider kit is 3 years old now. Plugs, wires, rotor and cap have maybe 15k on them.

I haven't had time to look at much yet but if anyone has an idea of where to start on this one let me know. I'm suspecting bad gas since the problem only occurs after the heat sink when you shut her down hot. I've had some real problems with vapor lock in the summer with ethanol added gas but those were a hard lock on a hot shut down, on a 100 degree day and nothing like this.

Chris Stewart · 02-08-2011, 06:09 AM

You might look at the Idle Air Control (IAC) on the left side of the throttle too.

old_master · 02-08-2011, 03:42 PM

If the IAC is OK, here are some other things to check:

No particular order other than how they popped into my head

The EGR valve might have a poor seal; cleaning with throttle body cleaner or carb spray usually takes care of it.

Try wiggling the connector at the ECT, (engine coolant sensor for the ECM near the thermostat) while the engine is acting up. Push on it, pull on it, wiggle it etc. I've seen several with a loose fitting connector.

Condensation on the under side of the distributor cap can cause crossfire after a hot soak. Make sure the vent hole screens are removed inside the distributor.

Not likely, but it's possible that the ignition module heat sink compound is all crusty and not transfering the heat away from the module. The IM is very sensitive to heat. If the module gets too hot it can operate erratically. If it overheats, you won't get spark at all. Radio shack has heat sink compound in a small tube, (part #276-1372). http://www.radioshack.com/product/in...ductId=2102858

Remove the module, clean off the old stuff with a rag and isopropyl rubbing alcohol, smear on the new compound and reinstall.

Chris Stewart · 02-09-2011, 07:26 AM

Those are some good ones OM.

ericn1300 · 02-09-2011, 07:35 PM

Well thanks Chris for mentioning the most expensive part first. I pulled the IAC and cleaned the pintle head and O ring, lubricated the ring and reseated the electrical connecter. According to my repair guide you need an IAC tester to really check it out.

When Old Master mentioned condensation in the distributor cap it was like a bingo moment. The last time I drove it was before Christmas on a rainy day and I noticed a slight miss. I thought to my self then that I needed to check for condensation in the cap but after a few libations at the Christmas party and a designated driver taking me home I forgot all about it until OM's post. The girls have probably been driving it like that for months.

Sure enough, there was corrosion inside the cap, my daughters boy friend who did the last tune up had used after market parts. The cap he installed had copper spark plug wire posts instead of aluminum like the OEM, that had turned green and had corrosion build up from electrolysis. I replaced the cap and rotor with AC-Delco but, alas, the problem remains, although it does start better.

I didn't pull the EGR valve, I just sprayed carb cleaner around it with the engine running to check for leaks.

I checked the connector at the ECT, pulling it off, inspected it and re-seated it, and tried wiggling it while the problem occurs. I also watched the temp gauge while the problem was occurring and there were no fluctuations.

I'm not really sure where the Ignition Module heat sink is but I have lots of heat sink compound on hand since I'm an IT guy, just point me in the right direction.

I'm really leaning towards the idea of bad gas, between the winter blends, the ethanol and my cheap 19 yr old buying the cheapest gas it's a real possibility. The tank is a little over a quarter but I think I'll drain it off tomorrow and start with fresh gas. Thanks for the old tip on how to drain the tank Chris, just use the fuel pump. I bought a clip on tire chuck for the zert connector and have some old air hose to use. I'll use it to fill the lawn mower next spring too.

I'll keep you guys informed, but if you have any more ideas toss them out. This baby only has 246K on it now, the lowest mileage vehicle in my fleet.

old_master · 02-09-2011, 07:52 PM

Eric, Crusty heat sink compound is a long shot, but if it fixes it, it's a cheap fix. The HEI ignition module is inside the distributor on 1992 W engines, the black thing in this image:

Remove the cap and rotor, both connectors, both screws.

There are two vent holes in the base, kinda tough to see when the distributor is installed, but you can feel 'em and put some compressed air to 'em. Gotta be clear, if not, that's why condensation builds up.

Chris Stewart · 02-10-2011, 07:58 PM

There's mention of the coolant temperature sensor and MAP sensor contributing to the problem too.
Do you still have your FSM to get values and check with a DVOM Eric?

ericn1300 · 02-10-2011, 08:13 PM

Yeah, I checked the values on both and they are fine. I took off the map and cleaned the vacuum orifice, it was a little cruddy. I also drained off the gas and filled up with premium no ethanol gas and pulled the ignition module and cleaned and coated it with new compound and it still does it.

I broke down and called my dads mechanic, described the problem and he said "I know exactly what it is, bring it over in the morning." He thinks it's the ignition switch, not the key and tumbler but the electrical side of the switch that needs to be replaced. I'll let you know what happens.

old_master · 02-10-2011, 08:22 PM

Eric, Faulty ignition switch is a very common problem on the 2nd gen's, especially 97. Never heard of it on 1st gen S&T body but what the hell, I suppose it's possible. Let us know, I'm curious.

Chris Stewart · 02-11-2011, 06:48 AM

There was something about disconnecting the timing wire, like to set the initial ignition timing, to determine if the distributor module was bad. If after disconnecting it, the engine smoothed out meant the module was bad.

A bad module in my little '86 Cutlass Ciera w/Ponitac Iron Duke 4 cyl. caused similiar symptoms...the computer couldn't find #1 cylinder.

Chris Stewart · 02-12-2011, 06:40 AM

I just remembered, I knocked the knock sensor loose, right next to #5 sparkplug while changing sparkplugs...well it kinda fell apart when I got against it with the sparkplug socket. The clip wouldn't hold the pin in the little tube and the engine ran like crap until I held it in place with a stick.
You may remember this Eric, I used 3 sizes of vacuum line to hold it in place and still there today.

ericn1300 · 02-15-2011, 03:36 PM

Well none of us were even close. Turned out to be the fuel pump relay cutting in and out when it got hot. Couldn't see it on the pressure gauge it was happening so fast, he found it with the scanner while the problem was happening. Not to bad, $12 bucks for parts and $40 for the diagnostic fees. My wife is making him cookies too.

Chris Stewart · 02-15-2011, 06:43 PM

Very good, we'll take that and add it to the trick bag.
Must be a pretty good scanner, do you know what brand?

old_master · 02-15-2011, 06:54 PM

Eric,
The relay shouldn't get hot. If the new one gets hot, check resistance in the circuits: grey wire should show less than 5 ohms from the relay to the pump. The black ground wire at the module should show less than 5 ohms resistance to ground. If those check out OK, check amperage draw on the pump, should be around 6 amps maximum.

ericn1300 · 02-15-2011, 07:33 PM

Quote:

Originally Posted by old_master

Eric,
The relay shouldn't get hot. If the new one gets hot, check resistance in the circuits: grey wire should show less than 5 ohms from the relay to the pump. The black ground wire at the module should show less than 5 ohms resistance to ground. If those check out OK, check amperage draw on the pump, should be around 6 amps maximum.

Thanks for the quick post O.M. the problem is not fixed. It started surging and pulling after 5 miles on the drive home and stalled as I pulled into the driveway. I think we're looking at another fuel pump. I know how to check resistance but how do you check the amperage draw?

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