89 TBI 350 stumbling around cruise

billygraves · 08-08-2018

edit

**89S10_Project** · 08-09-2018

Seems I misremembered- I had this problem long ago and never addressed it fully, it's just gotten worse:
http://www.gearhead-efi.com/Fuel-Inj...g-Log-attached

**steveo** · 08-09-2018

Originally Posted by billygraves

As written

get some plastic pliers and disconnect one plug wire at a time at idle, make sure it's running on all cylinders evenly

I offer a suggestion that will function for cylinder RPM drop that will not shock you. I've had these plastic pliers conduct and shock me.

i have a huge amount of trouble imagining spark voltage conducting itself through nearly 6" of dry plastic, especially after having to jump through a spark plug boot. and if it did, it should suffer such resistance that it'd be like touching a 9v battery.

i've use them tons of times, maybe over a thousand plug wires by now, never a tickle

maybe they were wet or oily?

**1project2many** · 08-09-2018

I've been shocked using plastic pliers also. Maybe it's just the universe taking advantage of the opportunity to mess with me. I've been shocked so damn many times it's not even funny anymore.

Well, I should say it's not funny to me. There's no end to the amusement I generate for spectators.

I can't see what suggestion was posted but I often use short lengths of vacuum tubing between plug wire and coil then use a test light from ground to the vacuum hose. I am also likely to use a grounded test light at the end of the spark plug boot if I choose to disconnect the plug wire while the engine is running.

**jim_in_dorris** · 08-10-2018

Originally Posted by 1project2many

I've been shocked using plastic pliers also. Maybe it's just the universe taking advantage of the opportunity to mess with me. I've been shocked so damn many times it's not even funny anymore.

Well, I should say it's not funny to me. There's no end to the amusement I generate for spectators.

I can't see what suggestion was posted but I often use short lengths of vacuum tubing between plug wire and coil then use a test light from ground to the vacuum hose. I am also likely to use a grounded test light at the end of the spark plug boot if I choose to disconnect the plug wire while the engine is running.

I fought that problem for years in my truck. It turned out to be both heads were cracked at the exhaust seats. And after it warmed up it would miss/ stumble at idle and light throttle. 193 tmi heads are prone to crack at the exhaust seats. My 2 cents

**89S10_Project** · 08-10-2018

Originally Posted by jim_in_dorris

I fought that problem for years in my truck. It turned out to be both heads were cracked at the exhaust seats. And after it warmed up it would miss/ stumble at idle and light throttle. 193 tmi heads are prone to crack at the exhaust seats. My 2 cents

Are you referring to my problem, it's not clear given the quote above your post.

I haven't been able to install the new grounds yet (owing to work and weather), but I have fabricated a few of them. One thing I did notice is when I relocated the sensor grounds from the thermostat bolt to the manifold bolt nearby, apparently I didn't run a ground from there off to the battery/body. So that is a HIGHLY suspect potential cause of this issue. Some would say relocating the grounds form the thermostat bolt is the issue you'll just never convince me a bolt threaded into an aluminum manifold is any better a ground than using a bolt going into the iron head (which, if we are being picky, the manifold was bolted into, so it should actually be a BETTER ground as it cuts down on the chain of grounds to get back to the negative terminal on the battery. ... well, you know, if I'd actually run that darn wire ;) )

This is clearly going to be the FIRST ground I improve. I built a 2-GA cable out of welding cable with a copper lug hammer-crimped to it and soldered (honestly, solder would be just fine on its own, and I've built many a cable that way) with marine-grade heatshrink over 3M electrical tape to seal against the weather.

**jim_in_dorris** · 08-11-2018

Originally Posted by 89S10_Project

Are you referring to my problem, it's not clear given the quote above your post.

I haven't been able to install the new grounds yet (owing to work and weather), but I have fabricated a few of them. One thing I did notice is when I relocated the sensor grounds from the thermostat bolt to the manifold bolt nearby, apparently I didn't run a ground from there off to the battery/body. So that is a HIGHLY suspect potential cause of this issue. Some would say relocating the grounds form the thermostat bolt is the issue you'll just never convince me a bolt threaded into an aluminum manifold is any better a ground than using a bolt going into the iron head (which, if we are being picky, the manifold was bolted into, so it should actually be a BETTER ground as it cuts down on the chain of grounds to get back to the negative terminal on the battery. ... well, you know, if I'd actually run that darn wire ;) )

This is clearly going to be the FIRST ground I improve. I built a 2-GA cable out of welding cable with a copper lug hammer-crimped to it and soldered (honestly, solder would be just fine on its own, and I've built many a cable that way) with marine-grade heatshrink over 3M electrical tape to seal against the weather.

Doing this on my phone, only gives me the option of reply with quote. I also replaced all the grounds and power with 2 GA wire fixed my low voltage problems, but not the stumble. I only found the problem after a backfire caused a small fire in the engine compartment and I decided to tear down the motor and freshen it up. Both heads went to the machine shop for a valve job, and both were cracked. Not say that is your problem, but it is a possibility

**89S10_Project** · 08-11-2018

I hear you. I am not backfiring through the intake, but the exhaust. This seems to me that it is caused by excess fuel in the exhaust , which gets hot and occasionally explodes.