95 Chevy 350 TBI acceleration problems

Symptoms are as follows:

When first started it runs fine for a few seconds then just dies like the switch was turned off. Cranks back up pretty easy again but idles high (1500RPM) for a bit then comes down and may idle fine for ever then it sometimes gets rough and dies. If I put it in gear or turn on the AC it gets rough and dies.

Driving it has trouble accelerating at low RPM. When I step on the throttle it bogs, grumbles and sometimes backfires (through the intake I think) but then it takes off like a dragster. Temperature only seems to make a slight difference but I do notice some improvement with the Coolant Sensor disconnected (on the intake manifold).

New plugs, coil, cap, rotor and wires New Cat. Convert New fuel filter- Fuel pressure is roughly 10 PSI (book spec-9-12) Removed EGR and it works nice and smooth Checked values of the MAP, Coolant sensor, Throttle position sensor, Idle air thingy and all seem to be with in spec (per tech manual) did the best I could with my multimeter by myself.

On one occasion (early morning going to work) it back fired and (slightly bigger than normal) and took off like a "Bat out of Hell" and worked like new for a couple days.

At high speeds it fluctuates. It sometimes works right or some times to maintain even throttle or increase speed it takes enough throttle to drop in to passing gear.

Someone suggested rechecking the fuel pressure by pinching off the return line to see if pressure increases by 4-6 PSI. That puzzles me. Back when I first checked the fuel pressure, I did so with the engine off and running and it held pretty steady at all times. What would be different by pinching the return line?

Had a shop run diagnostics for 2 hours but never found the problem. Sometimes I swear it acts like weak spark or fouled plugs. I have watch the fuel spray in the TBI for long periods of time with out any deviation, even when put under a load. It is my understanding that the TBI pulsing is controlled by the distributer and I wonder if there could be a problem there? In the fuse box the fuel pressure regulator box gets hot (uncomfortable to touch but no injury). Is that a problem? The ones surrounding it do not.

I am at the point of replacing the fuel pump and or the TBI, but I would like some more opinions or advise if any one has expertise or had experienced similar problems.

Thanks in advance.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

you should be able to go have the codes read, no?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

edgar wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

edgar wrote:

back. He checked every thing he could think of for a couple hours but never found the problem.

Reason for the different name: I have 2 e-mail accounts one at work and one at home. I posted this question while at work as "rong". I am replying at home as "welder"

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

rong wrote:

I think I would try unplugging the MAP (elect plug) and driving it to see if it does better. The light will be on but it should run fairly good. If it runs good with it disconnected and bad with it connected then...well...replace it :) Also check the vac to it closely. Also, the TPS, did you check it through its entire range? slowly? Some of those TBIs had a bad problem with the tbi base gasket going bad too. Not sure of the years (seams like late 80s)but it would make it do all kinds of goofy stuff.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

rong wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

rong wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

rong wrote:

Have you changed your fuel filter? Is there any debrie in your fuel tank? Are there any shorts in your plug wires? Are there any shorts between the distributor and TBI?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.