Help with ignition/electrical problem - New Development

[LeoneSM]

I've been having a very intermittent problem with my '87. It's only done it a handful of times in the past few months but it's something I need to resolve. The truck will sometimes cut off at low rpms while I'm turning. It usually happens as I'm pulling into a parking spot or something similar. It's never done it while sitting in traffic or when the steering wheel is straight and I never have a problem when driving at speed. The truck always cranks right back up without a problem. I do notice that my voltmeter jumps around a little bit at idle but I've never noticed it drop below 12 and shows 13-14 while driving.

Where do I need to start looking? What would cause that? Ignition switch or module maybe? The electrical on the truck is basically original and hasn't been hacked up or modified with the exception of a radio and lights. Hoping someone else has had a similar problem and can point me in the right direction. Thanks

 

[6872xtc]

I don't have any solid ideas, but I start thinking about what may shift during a turn to make it drop the voltage for a half of a second. I believe that I am just throwing out stuff, but maybe check the charge wire, all of the cab power wiring, maybe the positive cable too?

If you are positive that it is an electrical shut off symptom, maybe it is something that has a partial shirt when the body moves during a corner?

 

[LeoneSM]

I could be completely wrong, but I'm thinking it's something shorting inside the truck that's causing the problem. I've checked all of the under hood cables and connections and all look to be in good shape and solid. When it happens, it's like the key is turned to the off position. The truck goes completely dead, no lights, no radio, nothing.

If it were the alternator dropping output at low RPM, the battery should keep the truck running. The battery shows no sign of weakness and it cranks up strong immediately after. The fact that it only does it when it's turning is pointing me away from the alternator, too.

If it were something shifting under the hood, I would think it would be more prone to do it while the truck was moving faster. I've taken it through fields and down rough dirt roads and I don't have any problems in those situations.

Could the ignition switch itself be bad? Maybe something rubbing the steering shaft inside the column? I certainly appreciate the input. I'm just rambling and thinking out loud here trying to figure out where to start

 

[rampage]

Could be a broken plate inside the battery that shorts out on a turn.

I also remember someone else had a similar problem many years ago. Think it turned out to be a broken baffle inside the gas tank.

 

[6872xtc]

I was just trying to think of something that would drop the voltage below 10 for a second, just long enough to kill the ECM, but also cause a fluxuation in the volts as well. I think the chance of the steering shaft rubbing a wire for the ignition, inside the cab, is very slim due to the ignition switch being on top of the column. But that would not exclude the switch being bad. It could cut out, then work after restart.
That could be a place to start? ???

 

[southernspeed]

How's your idle speed? Turning at slow speed puts extra load on the motor from the pump which could easily stall the motor. Is the motor running well generally?

 

[LeoneSM]

I'm going to look into all of this. I don't think it's the idle speed but it's still a possibility. I bought the truck and drove it 500 miles home and have had it sitting in Atlanta traffic for an hour without problem. I've got plugs, wires, cap, rotor and a new coil going into it this weekend, so I'm going to make sure all the tune up stuff is working properly.

 

[LeoneSM]

How's your idle speed? Turning at slow speed puts extra load on the motor from the pump which could easily stall the motor. Is the motor running well generally?

southernspeed for the win. The problem has been getting progressively worse and shown itself a little more. It's something to do with the idle speed that's causing the truck to die and I guess the added load while turning was what was initially causing the truck to die. It's now been having the same problem when it's in gear and stopped in traffic. It does fine if you're just driving normally or aren't stopped for longer than 30 seconds or so. Any longer than that and the RPMs seem to gradually decrease until the truck cuts off. It doesn't idle rough or sputter but the RPMs will kind of jump down until the truck dies. Keeping my foot on the pedal a little will make it idle normally. It idles in park with no problems at all. Seems to be worse when I've been driving the truck for a while.

I replaced the IAC and it didn't help. I've checked for vacuum leaks by spraying carb cleaner on the lines and around the base of the throttle body to see if it would have any impact on the idle speed and it didn't. I don't want to throw parts at it but this is driving me nuts. I did the IAC reset but didn't mess with the minimum air. I figure it didn't have a problem until recently so it's probably not something I need to be messing with. Maybe MAP sensor? TPS? Where do I go from here? I don't have an ALDL cable...

 

[southernspeed]

Did you change your plugs, dizzy cap/rotor etc? How's the coolant temp? If it's running cool due to an open 'stat it'll throw too much fuel in when warm and that'll lead to a slowing rpm and stall.

 

[southernspeed]

One more thing to check is the EGR valve. If the diaphragm has split you'll get an air leak from that. Pull the hose off the top of the valve and push a finger up underneath the EGR valve body, pushing the diaphragm right up, then put another finger over the hole where you took the hose off, sealing it. The valve should stay up. If you feel it drop back down then the diaphragm is split. I've just replaced mine ( I had similar problems to you). I got a genuine ACDelco one from Amazon.

 

[LeoneSM]

I'll look into the EGR. I replaced all of the tune up stuff with ACDelco Parts. Distributor cap, rotor button, plugs, wires, air filter, PCV and now IAC. Only thing not Delco was the coil - I used a Pertronix. Truck does seem to run a little bit more power but otherwise is unchanged.

Coolant temp stays consistent in the 190-200ish range. Truck cranks up and idles higher when it's cold and then the idle speed in park is normal once it reaches operating temps.

 

[black dawg]

I would clean the throttle body real well, including the IAC passage. Also do the min Idle adjustment procedure. Do you have access to a scan tool?

 

[southernspeed]

Coolant temp stays consistent in the 190-200ish range. Truck cranks up and idles higher when it's cold and then the idle speed in park is normal once it reaches operating temps.

Mine was the same. Even when it would slow and die when hot, it would fire right back up and idle, but it got to the stage where just putting it in drive after it stalled would make it die. I had to a 1900 mile trip standing on the brake and giving it gas every time I put it in drive when hot. It was fine cold.

 

[LeoneSM]

I would clean the throttle body real well, including the IAC passage. Also do the min Idle adjustment procedure. Do you have access to a scan tool?

I don't have a scan tool. I did the IAC reset - jumped the A/B terminal, turned key on, unplugged IAC, turned key off, removed jumper, cranked truck. Let truck run for a minute then turned off and reconnected IAC. This didn't have any impact on the problem at hand. Since it was set at the same point and worked fine a short while ago, I'm assuming the idle speed/min air doesn't need adjustment and isn't the root cause.

 

[southernspeed]

Something else that could cause the problem is the magnetic trigger in the dizzy going bad/weak. I've not had that problem but I've heard it being a problem for some. It would only worsen still in a hot environment , hence only being a problem with a hot motor. Just a thought! :-)

 

[LeoneSM]

I'm going to call this one resolved. I pulled and attempted to check the EGR valve but mine had very small holes in the back and I couldn't fit my fat fingers in to push on the diaphragm to test. I had bought a new one so that I was prepared if it was bad and went ahead and threw that on there. That was three weeks ago or so. I've driven the truck on a 3+ hour trip and numerous stop and go errands in a bunch of different driving scenarios and haven't been able to duplicate the idle problem. Figured I'd follow up for anyone else having similar issues.

For anyone replacing the EGR, don't bother spending money on an ACDelco part. The only thing ACD was the box. The part itself was made in China and didn't have any ACD markings. The part number stamped into the physical part didn't even match the ACD number. I'm sure I could have bought the store brand part and it would have been the same thing in a cheaper box.

Thanks for all of the help