Surging and bucking when warmed up

[short1500]

When did you check the base ignition timing?


When it was me, I bought a used Snap-On Solus Pro from a seller on eBay.

At that time, $350 shipped to my door with a heap of accessories, a rechargeable battery that worked, the instructional DVDs, and a big plastic suitcase to carry it around in. Good from 1980 1/2 to 2007.

As said...there are other solutions.

I have not checked the base timing at all. I will be installing a new distributor today. What should timing be? Also I'll have to save up to buy the said obd scanner.

 

[Schurkey]

I have not checked the base timing at all. I will be installing a new distributor today. What should timing be?

Initial timing with the EST wire disconnected should be "0" or TDC. Some folks like a degree or three of extra advance.

Also I'll have to save up to buy the said obd scanner.

If you're buying a Snap-On Solus Pro or other "used" scanner, get one with the software new enough for any vehicle you're likely to work on, as the Snappy is NOT upgradeable any more. Snap-On has ended support for them.

You'll want the various accessories, too. A look at eBay auctions will give you an idea of what's available and needed.

 

[short1500]

Installed new distributor and set timing. It didn't do squat.

 

[95 Tahoe]

Have you ruled out vacuum leaks? A bad spark plug can cause a lot of issues too.

 

[short1500]

Have you ruled out vacuum leaks? A bad spark plug can cause a lot of issues too.

All new spark plugs and haven't found a vacuum leak.

 

[udidwht]

Fuel pressure check ok?

 

[DerekTheGreat]

Have you verified fuel pressure and base idle yet? If the base idle is set too low, the idle will end up surging. I had a 454 TBI do that.

Another thing you can check is the throttle position sensor. When mine went bad ('89 K1500, 5.7L), it caused a surge. What was happening is that it was throwing erratic voltages back to the ECM and as it did that, the ECM was opening and closing the IAC. Found it thanks to a scan tool.

 

[short1500]

Fuel pressure check ok?

Have not checked fuel pressure yet. Pump assembly and filter are new. Will check pressure to verify its good.

 

[short1500]

Have you verified fuel pressure and base idle yet? If the base idle is set too low, the idle will end up surging. I had a 454 TBI do that.

Another thing you can check is the throttle position sensor. When mine went bad ('89 K1500, 5.7L), it caused a surge. What was happening is that it was throwing erratic voltages back to the ECM and as it did that, the ECM was opening and closing the IAC. Found it thanks to a scan tool.

I checked TPS with volt meter and found no inconsistences with voltage while checking. In the process of trying to get my hands on a scanner.

 

[DerekTheGreat]

Would probably be best to use a scanner and then leave it in test mode while you drive around, once you verify fuel pressure. I initially checked my TPS with a sweep and it was fine. But toward the end when I was just about ready to pull my hair out I decided to drive around for the day with the brick sitting next to me. I was at a light when it started to act up and saw the TPS voltage fluctuating a bit along with IAC counts, bingo.