88 Burb R10 stumbling under load

[cabledawg]

Like the title says, my truck recently started having issues under load. Idling was never super smooth but I'm not seeing much difference there. Same with no load revving. Once out of first gear though, it sputters and stumbles pretty bad under load. I can ease into the throttle and still accelerate, but anything more than about 20% throttle and it's got problems. Started a few months back and originally only did it after a heavy rainstorm. Now it's pretty much all the time. Converted to manual in 2008 so I don't think it's tranny slip.

It's still pretty much a stock engine with a few aftermarket parts. Still TBI, but I have a Performer intake with riser, short headers (O2 sensor on the driver side), 56k volt coil (IIRC) and a few little odds and ends that have been on there since 2007 when I had to replace the original engine. I have a OBD cable but my laptop battery died so testing can only be done in the driveway with 110 power.

It doesn't smell like it's running rich so I'm wondering if it's leaned out and opening up the throttle screws up the mixture. On occasion it sounds like it's backfiring. I've already checked vacuum hoses and don't see anything disconnected or obviously broken/damaged. So I want to see what you guys think might be the problem before I waste time looking in the wrong place or throwing money away on parts that were still good. Thanks in advance.

 

[Bent77]

The “rainstorm” timing may lead you to finding something that may have gotten wet in the ignition side

But it sounds to me like it’s not getting enough fuel, or that the throttle position sensor is not working so it’s under fueled

 

[diesel4me]

Old plug wires and or distributor cap & rotor,and that super duper ignition coil will make it more likely to have issues in wet weather..

My '66 Buick wouldn't run on all cylinders on rainy days after I put an Accel "Super Coil" and new plug wires on it..you could see the spark jump right thru the wire's insulation to the engine block ,rather than fire the plugs under a load.it would idle crappy,and want to snuff out when you went to take off or climb a hill,you could hear and feel the cylinders stop firing..

I put the original Delco coil back on it and the problem vanished..
You don't really need 50,000 volts,20,000 is enough to fire the plugs fine..that high output coil might be feeding pulses back to the ECM too and confusing it too...

 

[dyeager535]

What's fuel pressure?

Notice if it runs any better with a full tank? In-tank hose splitting is fairly common if it's pre-ethanol hose. Mine got somewhat progressively worse, I assume as the hose split worse.

 

[rampage]

Yep, just about to say check the fuel pressure, IIRC GM says between 9-13 psi - someone correct me if I’m wrong.
Another thing to check is a blocked catalytic converter. You might be able to rent an IR gun from your local parts store to check the temperature of the converter itself and also the pipes just before and after the converter. The temp should be higher after the converter as compared to before it. Follow step 6 here:
https://www.3geez.com/forum/3geez-accords/81802-how-diagnose-bad-catalytic-converter.html

 

[dyeager535]

Yep, just about to say check the fuel pressure, IIRC GM says between 9-13 psi - someone correct me if I’m wrong.
Another thing to check is a blocked catalytic converter. You might be able to rent an IR gun from your local parts store to check the temperature of the converter itself and also the pipes just before and after the converter. The temp should be higher after the converter as compared to before it. Follow step 6 here:
https://www.3geez.com/forum/3geez-accords/81802-how-diagnose-bad-catalytic-converter.html

Yes, 9-13 is spec, although most say 10-11 is about as low as you want to have it run good.

 

[cabledawg]

Didn't think about coil burning through the wires. Mine are 8mm but I cant remember how long ago I changed them. Easy check to do tonight. I haven't noticed a difference with full tank vs. low tank. I still have the fuel pressure sensor installed just need to hook up the gauge so I'll check that this weekend. No cat converters. Illegal I know but my state doesn't have sniffer or visual inspection.

I'll check the wires and fuel pressure and get back with you guys. Not sure how to check the throttle position sensor but I do have a spare TBI I can swap if nothing else seems to fix it.

 

[dyeager535]

Just do a good check underhood while you are there. Make sure everything that is supposed to be is connected (wiring, vacuum lines, etc), try and see if the TBI base gasket is falling apart, make sure any vacuum hoses are in good shape. You can also check the EGR for proper function, sometimes they get sticky. On the "normal" EGR you can reach up underneath it and push up and it should noticeably make the vehicle run worse.

 

[H20 Toie]

replace the fuel filter first, that little bugger can make you think you have a lot of other issues, i was positive my trans let go one time and only the fuel filter

 

[snowdriver]

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
That!!!!!!