Suburban driving me crazy!!!

[movietvet]

The cap and rotor is picky. What brand do you have on there?

 

[darksheep85]

The cap and rotor is picky. What brand do you have on there?

The ones that came with the Delphi distributor

 

[movietvet]

The ones that came with the Delphi distributor

Just seein' what might stick.

 

[Scooterwrench]

Remember this is obd 1. You can't get a live data readout. And there are no codes.

You can view live data with TunerPro RT and an ALDL to USB cable for your laptop. You can also datalog then play it back. TunerPro is a free program with a voluntary $40 registration fee and the cable will set you back about $60

 

[thinger2]

This will be a long post so, apologies in advance.

2 years ago I bought a 1993 suburban c2500 454TBI/4L80 that had 250k miles but was meticulously maintained. Southern truck so no rust. When I got it home, it didn't have very good oil pressure so I changed the oil pump hoping for the best. But it was actually the crank bearings were shot. So I had the engine and transmission rebuilt at the same time. The machine shop reused the cam and lifters because he said he didn't trust new camshaft metal. (I didn't know this till after I paid for it).

We then move from SC to NY

6 months later it wipes a cam lobe. So I replace the cam, lifters, rockers, and studs. Immediately upon startup it wiped the same lifter. So after being thoroughly disgusted with my situation, i bought a ATK reman engine at NAPA and had a local shop install it. So heres the rundown on new parts on the engine. NAPA brand distributor, coil, ngk iridium plugs, good wires, every sensor on the engine, no vacuum leaks, new fuel pump, timing set at 4°, tps set to spec. Ran great but had a slight miss and rpm would go up and down at idle. The miss was causing the tach to bounce when it would miss. And it would randomly miss at low rpm low load situations, like 60mph on flat road in overdrive. Ran it like that till it was time for my break-in oil change at the place that did the engine. They change the oil and go to back it out....no reverse. Great.

So now 1 year old transmission needs rebuilt again. Took it apart and found the plunger that engages the 1/R band had pounded itself into oblivion and something else in the transmission was cracked. So, full rebuild.

Still using the torque converter from 1st rebuild 2 years prior.

So now engine and trans are fresh and new again. What feels like a misfire is still there, so I've changed the NAPA distributor out for a Delphi. The bouncing tach and fluctuating idle have gone away, but this thing still feels like it has a miss at cruising speed (40-70+). But it's different. I don't know how to explain it. If you floor it from a dead stop, it takes off with no problem, bangs through the gears, and has plenty of power. But if you set the cruise at 60, it gets this random stumble that is driving me nuts.

I've thought maybe the ngk iridium plugs are just to much for it, but that doesn't really make sense to me. They should be fine, they just last longer. I've never had a vehicle with torque converter problems before, and I don't know if that's what this could possibly be. It's not making a "noise" of any kind. It feels like the engine dies for a 10th of a second.

I'm too far into this thing financially to just give up. I bought this to tow with and I need it to do its job. PLEASE HELP!!!

Disconnect and clean or replace every one of the grounds.
All of them.
If you have not personally replaced the battery cables and cleaned every one of the grounds they are bad.
The ground cable from the back of the passenger side head to a stud on the firewall will cause problems.
The manifold grounds will cause problems.
Just one bad heat cracked plug boot that doesnt have dieltric grease on it will arc to the exhaust manifold.
Crossed plug wires can do it.
When you buy one of these trucks the very first thing to do is to inspect and replace every one of the grounds.
They have an undeserved reputation for having bad wiring.
The wiring harness itself is pretty stout.
The connections are bad
That bad reputation comes from the fact that these trucks are 30 years old and the tbi system is very ground and voltage sensitive.
Back in the day you could drive a carbed engine with bad grounds and the headlights were weak and the dope light didnt work and the dash flickered and it didnt matter.
You cant do that with a TBI.
This is why people get frustrated and lost after firing the parts cannon at these trucks.
Every electrical sensor you replace will not function if the ground is bad or weak.
When you first buy a gmt400, Pick a ground circuit and fix it.
Then next weekend, fix another ground.
And then you will be done.
This weekend I am going after the bed grounds.
Because its been about ten years.
Its the grounds, its the grounds, its the grounds.
Fix the grounds and then you can try to diagnose the problem.

 

[Schurkey]

1993 suburban c2500 454TBI/4L80

ngk iridium plugs

Nice plugs. Waste of money, but nothing wrong with them assuming they're the right ones for the application. Just overly-fancy for a TBI.

Ran great but had a slight miss and rpm would go up and down at idle. The miss was causing the tach to bounce when it would miss.

Indicates an ignition problem...

What feels like a misfire is still there, so I've changed the NAPA distributor out for a Delphi. The bouncing tach and fluctuating idle have gone away,

...but you've (at least partially) taken care of that problem.

but this thing still feels like it has a miss at cruising speed (40-70+). But it's different. I don't know how to explain it. If you floor it from a dead stop, it takes off with no problem, bangs through the gears, and has plenty of power. But if you set the cruise at 60, it gets this random stumble that is driving me nuts.

Stumble, or torque converter clutch engaging/disengaging?

I've thought maybe the ngk iridium plugs are just to much for it, but that doesn't really make sense to me. They should be fine, they just last longer.

They last longer on vehicles with ultra-precise fueling and ignition. TBI is better than carb, but not perfect enough to really benefit from Iridium plugs.

I've never had a vehicle with torque converter problems before, and I don't know if that's what this could possibly be. It's not making a "noise" of any kind. It feels like the engine dies for a 10th of a second.

I'm too far into this thing financially to just give up. I bought this to tow with and I need it to do its job. PLEASE HELP!!!

I suggest the "usual three". Details below.

Remember this is obd 1. You can't get a live data readout. And there are no codes.

Of course live data is available. Common misconception, though. How do you think these vehicles got fixed when they were new?
Posts 14 and 15 of this thread...but the entire thread is kinda amusing.
www.automotiveforums.com/vbulletin/showthread.php?t=1146067

94 k2500 no low end power and horrible fuel mileage - Automotive Forums .com Car Chat

94 k2500 no low end power and horrible fuel mileage C/K

www.automotiveforums.com

Three things you need to do:

1. Verify fuel pressure when the engine is acting up.

2. Verify all "tune-up" procedures and parts. You've got a head-start on this with plugs, wires, cap and rotor, and initial timing. Still need to verify PCV system, EGR system, heated-air intake, (if applicable) electronic timing advance including knock sensor, Evap system, etc.

3. Connect a scan tool, find out what the computer wants you to know. Especially important will be sensor data and computer outputs when the engine is "stumbling". Fuel-trim data may or may not be important, but needs to be investigated. I'd be looking real hard at whether the computer is commanding the torque converter clutch to engage or disengage.

 

[darksheep85]

Nice plugs. Waste of money, but nothing wrong with them assuming they're the right ones for the application. Just overly-fancy for a TBI.


Indicates an ignition problem...


...but you've (at least partially) taken care of that problem.


Stumble, or torque converter clutch engaging/disengaging?


They last longer on vehicles with ultra-precise fueling and ignition. TBI is better than carb, but not perfect enough to really benefit from Iridium plugs.


I suggest the "usual three". Details below.


Of course live data is available. Common misconception, though. How do you think these vehicles got fixed when they were new?
Posts 14 and 15 of this thread...but the entire thread is kinda amusing.
www.automotiveforums.com/vbulletin/showthread.php?t=1146067

94 k2500 no low end power and horrible fuel mileage - Automotive Forums .com Car Chat

94 k2500 no low end power and horrible fuel mileage C/K

www.automotiveforums.com

Three things you need to do:

1. Verify fuel pressure when the engine is acting up.

2. Verify all "tune-up" procedures and parts. You've got a head-start on this with plugs, wires, cap and rotor, and initial timing. Still need to verify PCV system, EGR system, heated-air intake, (if applicable) electronic timing advance including knock sensor, Evap system, etc.

3. Connect a scan tool, find out what the computer wants you to know. Especially important will be sensor data and computer outputs when the engine is "stumbling". Fuel-trim data may or may not be important, but needs to be investigated. I'd be looking real hard at whether the computer is commanding the torque converter clutch to engage or disengage.

As far as "is it tcc lockup/disengage, or a miss?", when it does it the rpms don't waver at all. So I'm assuming it's a miss.

 

[Erik the Awful]

Iridium plugs are overkill for your setup, try some copper or platinum plugs instead, stick with AC Delco brand.

But, what reason is there that cheaper plugs will be better?

You're asking that question backwards. What reason is there that expensive plugs will be better?

As I understand it, Iridium plugs matter on wasted spark ignition systems. In a wasted spark ignition, matched pairs of cylinders fire their spark plugs at the same time. One is on the power stroke, the other is on the exhaust stroke. The spark travels from the coil, through the plug, into the block, through the other plug, and back to the coil. Current is flowing electrode-to-ground on one plug, and ground-to-electrode on the other. The plug where the current flows electrode-to-ground loses material from the electrode. An iridium plug resists that material transfer and lasts longer in that application.

Our trucks don't run wasted spark, so an iridium plug is wasted money.

 

[darksheep85]

Nice plugs. Waste of money, but nothing wrong with them assuming they're the right ones for the application. Just overly-fancy for a TBI.


Indicates an ignition problem...


...but you've (at least partially) taken care of that problem.


Stumble, or torque converter clutch engaging/disengaging?


They last longer on vehicles with ultra-precise fueling and ignition. TBI is better than carb, but not perfect enough to really benefit from Iridium plugs.


I suggest the "usual three". Details below.


Of course live data is available. Common misconception, though. How do you think these vehicles got fixed when they were new?
Posts 14 and 15 of this thread...but the entire thread is kinda amusing.
www.automotiveforums.com/vbulletin/showthread.php?t=1146067

94 k2500 no low end power and horrible fuel mileage - Automotive Forums .com Car Chat

94 k2500 no low end power and horrible fuel mileage C/K

www.automotiveforums.com

Three things you need to do:

1. Verify fuel pressure when the engine is acting up.

2. Verify all "tune-up" procedures and parts. You've got a head-start on this with plugs, wires, cap and rotor, and initial timing. Still need to verify PCV system, EGR system, heated-air intake, (if applicable) electronic timing advance including knock sensor, Evap system, etc.

3. Connect a scan tool, find out what the computer wants you to know. Especially important will be sensor data and computer outputs when the engine is "stumbling". Fuel-trim data may or may not be important, but needs to be investigated. I'd be looking real hard at whether the computer is commanding the torque converter clutch to engage or disengage.

as stated before, all sensors on engine and trans have been replaced while it was out. PCV valve is new with good hose. EGR has been removed and a bypass plate was put over the hole. But all electronic compoments are still hooked up and hoses connected and pinched shut, appropiately. Now, when i bought the truck, the evap system had been pretty much removed. the PO used the truck to compete in CB and shortwave radio competitons. the damn thing has 7 antenna mounts on it. But he removed the charcoal canister and cut the lines under the hood so he could install a driver side battery and run 2 batteries for his radio setup. Sox the gas tank doesnt purge like its supposed to. so i drilled a hole in the gas cap to let it vent.

 

[udidwht]

How are the injectors themselves? When is the last time they were serviced?

Another check the grounds. Clean, clean ,clean...