The Stupid Engine Questions Thread

[Betitseasy]

I'm working my way through the engine bay to clean up the idle on my "new" 95 K2500 Burb. Fixing vacuum leaks, cleaning the throttle body, new plugs/wires, IAC is in the mail, etc. But I'm not sure what some of these connections are for on the 7.4L.

The arrows are pointing to the line that snapped in half when I popped the end off the throttle body (it probably had a hairline crack that I didn't notice). What is it connected to in the bottom left, and does anyone know the vac line size to replace it?

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Same questions for these oily plugs on the back. They join into a tee fitting but I have no idea what they're doing. They don't fit well (old dried out rubber) which explains the oil, so I'd like to replace them, too. (EDIT: This is the MAP setup, isn't it?)

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I just don't know what terms to use to find replacements.

Edit: OH! Another dumb question. I just replaced the upper radiator hose because it sagged JUUUUUUUUST enough to interfere with the fan blade. You can probably guess how well THAT worked out. How is the hose supposed to be supported up and out of the way? A picture would probably be easiest, if someone's got one handy.

I'm working my way through the engine bay to clean up the idle on my "new" 95 K2500 Burb. Fixing vacuum leaks, cleaning the throttle body, new plugs/wires, IAC is in the mail, etc. But I'm not sure what some of these connections are for on the 7.4L.

The arrows are pointing to the line that snapped in half when I popped the end off the throttle body (it probably had a hairline crack that I didn't notice). What is it connected to in the bottom left, and does anyone know the vac line size to replace it?

You must be registered for see images attach

Same questions for these oily plugs on the back. They join into a tee fitting but I have no idea what they're doing. They don't fit well (old dried out rubber) which explains the oil, so I'd like to replace them, too. (EDIT: This is the MAP setup, isn't it?)

You must be registered for see images attach

I just don't know what terms to use to find replacements.

Edit: OH! Another dumb question. I just replaced the upper radiator hose because it sagged JUUUUUUUUST enough to interfere with the fan blade. You can probably guess how well THAT worked out. How is the hose supposed to be supported up and out of the way? A picture would probably be easiest, if someone's got one handy.

I'm not 100% about it, but a few people including me have the same dilemma with the extra wiring. After discussing some GMT400 history we concluded 1 set is for TBI engine components, and the other is for the Vortec. I have a 5.7 TBI, pre-cat O2 sensors, pick up coil and ignition control module external coil no crank or camshaft sensors but I have those plugs secured to the rest of the harness. Manual transfer case floor shifter. I have 96 dash with both airbags, and a solid button space for push button 4x4. ECMs fuse box are different, TBI has relay center on passenger side firewall, Vortec has relays and box mounted on driver's side inner fender. Seen people complain about start and die situation caused by a wire shorting out in the security system, but never thought of that being the issue because their truck didn't have that option. My cuz had a 99 interior and exterior, 2 afternoons motor and drivetrain went right into a 98.

 

[jswiftsr]

My truck is a 1993 1/2 ton 4x4 with a 4.3 v6 it has developed a random knock its quiet at start up it mainly does it under light acceleration but its alot louder than a spark knock I have narrowed it down to the area of the flywheel inspection cover or the oil pan with a mechanics stethoscope.

Now I have heard these engines had a problem with the flywheel or flywheel bolt that give off a rod knock type sound does anybody here have any other ideas or have heard of this type issue with the flywheel?

I have had a torque Converter bolt back out before....and it was hitting the block when it went around. Soundd just like a rod hammering in the crank. Tightened and torqued bolts.....solved the knock. I also had a bad engine dampener (harmonic balancer). Rubber came loose.....knocked just like a rod was coming loose. Installed a new dampener.....problem solved. Hope this helps.

 

[Godholio]

I'm not 100% about it, but a few people including me have the same dilemma with the extra wiring. After discussing some GMT400 history we concluded 1 set is for TBI engine components, and the other is for the Vortec. I have a 5.7 TBI, pre-cat O2 sensors, pick up coil and ignition control module external coil no crank or camshaft sensors but I have those plugs secured to the rest of the harness. Manual transfer case floor shifter. I have 96 dash with both airbags, and a solid button space for push button 4x4. ECMs fuse box are different, TBI has relay center on passenger side firewall, Vortec has relays and box mounted on driver's side inner fender. Seen people complain about start and die situation caused by a wire shorting out in the security system, but never thought of that being the issue because their truck didn't have that option. My cuz had a 99 interior and exterior, 2 afternoons motor and drivetrain went right into a 98.

I hadn't thought about the possibility of Vortec wiring. 95 was very much a transition year for these, and I know the General has done stranger things.
My relay box is on the driver's side (TBI). Passenger side has no electronics besides the battery.

 

[ben2go]

Stupid engine question. '89 5.7 auto trans. The truck seems to be over-fueling. The exhaust has a strong unburnt fuel smell. Recent tune-up. Fuel mileage is down. No check engine light. I feel like the o2 sensor may be the culprit or possibly the TBI isn't spraying as well as it appears to be when looking down the throttle plates with the engine running. Open to other suggestions.

 

[Schurkey]

How old is the O2 sensor?

Connect a scan tool, look at the data stream--O2 voltage, O2 crosscounts, Coolant temp sensor, anything else that looks abnormal.

If the exhaust "smells rich"...you've very likely got a failed catalytic converter. The question is whether it died a normal death from old-age, or whether it was murdered by misfiring cylinder(s).

 

[ben2go]

How old is the O2 sensor?

Connect a scan tool, look at the data stream--O2 voltage, O2 crosscounts, Coolant temp sensor, anything else that looks abnormal.

If the exhaust "smells rich"...you've very likely got a failed catalytic converter. The question is whether it died a normal death from old-age, or whether it was murdered by misfiring cylinder(s).

89 doesn't have a way to scan the computer and data log. I'm not even sure it's OBDI compliant. It's pre OBDII. O2 sensor is unknown age. Cat is OE to the truck.

 

[Schurkey]

89 doesn't have a way to scan the computer and data log.

Entirely incorrect. But you're not alone in thinking that.

Given a REAL scan tool and the proper software and system connectors, I can view the data stream on most GM computer-controlled cars and trucks back to '80 1/2.

Here's a link to a previous discussion on another forum where I describe using my scan tool on my '88 K1500. Read the whole thread, but specifically post 14 and 15.

http://www.automotiveforums.com/vbulletin/showthread.php?t=1146067

I'm not even sure it's OBDI compliant. It's pre OBDII.

OBD-II started in '96, so of course it's OBD-1.

O2 sensor is unknown age. Cat is OE to the truck.

In that case, both are due for replacement. The cat is decades overdue. There's a very good chance that there's no pellets left in the thing. It was not uncommon to see pellets spitting out the tailpipe on older GM vehicles. The muffler would trap them (for awhile) and rattle like a maraca.

REPLACE the $13 O2 sensor, SCAN the engine, FIX what you find wrong (if anything), and when the engine runs right again, REPLACE the converter. When it was my '88, I used a modern, monolithic "high-flow" cat instead of a pellet-type.

 

[ben2go]

Entirely incorrect. But you're not alone in thinking that.

Given a REAL scan tool and the proper software and system connectors, I can view the data stream on most GM computer-controlled cars and trucks back to '80 1/2.

Here's a link to a previous discussion on another forum where I describe using my scan tool on my '88 K1500. Read the whole thread, but specifically post 14 and 15.

http://www.automotiveforums.com/vbulletin/showthread.php?t=1146067



OBD-II started in '96, so of course it's OBD-1.


In that case, both are due for replacement. The cat is decades overdue. There's a very good chance that there's no pellets left in the thing. It was not uncommon to see pellets spitting out the tailpipe on older GM vehicles. The muffler would trap them (for awhile) and rattle like a maraca.

REPLACE the $13 O2 sensor, SCAN the engine, FIX what you find wrong (if anything), and when the engine runs right again, REPLACE the converter. When it was my '88, I used a modern, monolithic "high-flow" cat instead of a pellet-type.

Thanks. I'll have a look at that thread after Xmas.

 

[Ivan90]

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EGR valve... over time my '93 K1500 5.7L engine started coughing/stuttering/surging especially at low idle. I changed spark plugs and wires, distributor cap and rotor, O2 sensor, map sensor, fuel pump, rebuilt the TBI, and fixed the timing, still the engine ran rough.

Then I accidentally broke the brittle EGR tube that connects the valve to the solenoid as shown in the picture - the problem went away, no more engine stutters. Funny breaking something seemed to fix the problem. I repaired the tube and the engine stutters returned, so I put the broken tube back on and let it be. I assume my EGR valve and/or EGR solenoid are causing problems, or maybe its something else.

Two stupid questions: 1) what does this EGR valve and solenoid do for me - are they important? and 2) should I replace them or just leave it alone with the broken tube? Appreciate any insight.

 

[PlayingWithTBI]

1) what does this EGR valve and solenoid do for me - are they important?

The EGR was developed to reduce NOx, by cooling the combustion chamber, so they could pass emissions. Some people say it increases MPGs too.

2) should I replace them or just leave it alone with the broken tube?

You obviously don't have emissions testing where you live? If so, you'll need to fix it. Otherwise, you could disconnect the electrical connector going to the EGR solenoid so you don't create a vacuum leak when the PCM tells it to open. You'll also get a MALF code (32) and an SES light if it doesn't work. On these older OBDI PCMs the light may not stay on but, it'll store the code for ~30 - 40 key cycles, or after you disconnect the battery for a while.