Engine rough

[paylov]

Hey everyone,

I posted a few weeks back about how my truck was missing basically its entire vacuum line system. I have added it all back, to include the MAP sensor, EGR solenoid, and evap solenoid. The engine it running real good at idle, however when you give it the slightest amount of gas, light trying to coast through my neigblhborhood, it acts like its starved of something. The truck gets very rough, low sounding idle(?). But when i give it a little more gas to start picking up speed then it clears up. But when coasting at that low speed and rpm or starting slow from a light or stop sign is when its acting up.

The truck is a 1994 k1500 5.7 350 tbi.

Any help to point me at what to look at next would be great. I have a feeling i might be missing something else but not sure. The engine was previously rebuilt a few thousand miles back, and seems to have been a little off sense, but that was before i got the truck.

Thanks

 

[kolgeirr]

As is typically recommended when things run poorly around here: check your fuel pressure. Also might be worth going over your vacuum system work again to make sure you don't still have a vacuum leak somewhere.

With the odd idle I'd also take a look at the idle air control valve and at least clean it up a bit. If it's sticky or not working you'll starve your engine of air when the throttle plate is closed at idle or coasting.

Can't hurt to put a code reader on the thing and see if it's logging any suspect data like misfires or old stored codes that aren't setting a CEL. Though I don't know how much info OBD1 provides.

 

[Schurkey]

Can't hurt to put a code reader SCAN TOOL on the thing and see if it's logging any suspect data

FIFY.

Yes, fuel pressure test, connect scan tool to verify all sensors especially TPS, MAP, and coolant temperature; and computer outputs.

How old are the usual "tune up" items such as spark plugs, plug wires, cap 'n' rotor? Has the initial timing been checked? Electronic spark advance verified? EGR works? Fuel filter, air filter, and PCV system checked?

 

[paylov]

FIFY.

Yes, fuel pressure test, connect scan tool to verify all sensors especially TPS, MAP, and coolant temperature; and computer outputs.

How old are the usual "tune up" items such as spark plugs, plug wires, cap 'n' rotor? Has the initial timing been checked? Electronic spark advance verified? EGR works? Fuel filter, air filter, and PCV system checked?

Im in the process of doing all the tune up stuff at the moment. Its all suppose to be fairly new, but i dont trust the guy before me to much anymore.

You have a recommendation for a good scan tool for the obd1 system?

 

[Schurkey]

I bought a Snap-On Solus Pro when my Snappy MTG2500 died.

I'd rather have a used/obsolete professional-grade tool than a brand-new consumer-grade tool. Not everyone will agree.

 

[kolgeirr]

The fancy tools are nice, but you can get pretty far with a $30 Bluetooth adapter and Torque Pro on your phone, at least for OBD2. Again not sure about OBD1, never had a vehicle of that vintage.

 

[FourEightZero]

You have a recommendation for a good scan tool for the obd1 system?

My OBD1 scan tool:

$200 laptop from the local university surplus store
$50 USB ALDL cable
(free) TunerPro RT (www.tunerpro.net)

I can see everything the computer senses and commands (including the tranny). Can also datalog so I'm not trying to look at a screen while driving (or have my buddy drive my truck).

 

[pressureangle]

Hey everyone,

I posted a few weeks back about how my truck was missing basically its entire vacuum line system. I have added it all back, to include the MAP sensor, EGR solenoid, and evap solenoid. The engine it running real good at idle, however when you give it the slightest amount of gas, light trying to coast through my neigblhborhood, it acts like its starved of something. The truck gets very rough, low sounding idle(?). But when i give it a little more gas to start picking up speed then it clears up. But when coasting at that low speed and rpm or starting slow from a light or stop sign is when its acting up.

The truck is a 1994 k1500 5.7 350 tbi.

Any help to point me at what to look at next would be great. I have a feeling i might be missing something else but not sure. The engine was previously rebuilt a few thousand miles back, and seems to have been a little off sense, but that was before i got the truck.

Thanks

Disconnect the EGR and test drive. Perhaps it's open when it shouldn't be, or after you reconnected it when it opened a piece of coal settled in it holding it open.