I have a 350 TBI in my 1952 Chevy truck. It was a fresh build 4 years ago and has maybe 5k on it. It has pretty much always had issues. I have just lived with them but want to solve them now.
The set up:
Stock motor, CPU and throttle body. It does have headers and no cats.
They symptoms:
1) The idle surges after a cold or cool start.
2) When cold outside and a cold start, it bogs down if you give it throttle.
3) Even when warm, if you floor the accelerator, it pauses and thinks about it.
4) When warm, if you stop and restart, it will only keep running if you give it extra throttle. After time this goes away.
My diagnostics/actions so far:
1) Fuel pressure is 11 PSI at idle.
2) I cleaned the throttle body
3) I removed and cleaned the EGR and checked all of it's lines for clogs and leaks
4) I teased the voltage on the temp sensor and it was 5 (weird number, I thought, but that seems to be what others report seeing)
5) I checked the timing but that's tough because I have a random timing cover on there so the marks are way, way off.
I have photos, I can shoot videos or answer any questions that might help solve this issue(s). And always willing to test out anything.
1st, I'd tell you to block off the EGR vavle, plug it's controller's vac line - GET RID OF IT - there is no need for it;
2nd, you have to find TDC and set the timing accordingly;
3rd, perform the IAC reset procedure.
Do you have anything to monitor live data? Things like coolant temp, intake temp and O2 sensor readings would be critical.
Almost forgot - is your vacuum steady via a gauge?
64nailhead: does the EGR controller not report to the ECU? If not, there is no pressure-related utility value to the EGR?
The vacuum is not regulated by any guage that I am aware of.
And I do not have any monitoring tools. Is there something you would recommend I order? I am a software engineer so I am interested in investing in the computer tools.
Hogg: there is one O2 sensor. It's in the driver's side exhaust pipe about 1 foot past the collector.
I have a 700r4, and my trans builder said he build it for that year range.
The O2 sensor is there.
As for the timing, I will hunt down a timing cover replacement and swap it out and adjust the timing from there.
As for the fuel pressure, I have the Carter p5001, which is an inline pump rated at 20 PSI and, according to Summit, made for this application. It's easy to replace that. Got any suggestions on a model?
Here's the full update on everything I have tried so far:
Adjusted:
1) Adjusted the timing
Replaced:
1) Replaced the temp sensor with a new one
2) Replaced the MAP sensor with a new one
3) Replaced the IAC with a new one
4) Replaced the ignition module with a back up copy
5) Replaced the TPS with a back up copy
Tried:
1) Removed the EGR completely (and left if off)
2) Unplugged the O2 sensor (and plugged it back in after testing)
3) Unplugged the MAP sensor (and plugged it back in after testing)
Tested/investigated:
1) I sprayed starter fluid everywhere and could not find any leaks in any lines or joints. Nothing.
2) Tested the fuel pressure - steady 11 PSI at all times
3) Pinched off (with my hands) the return gas line to drive the pressure up
4) Tested the MAP pressure - and even 20
5) The PCV valve is clean and functioning
What has "helped":
1) Unplugging the MAP sensor from the ECU ended the surging right away. Interesting?
2) Advanced the timing to 0. It was off by a good 15 degrees. That ending the surging right away. But I re-enabled the advance and it wouldn't start, so I had to retard it to get it to start and, of course, the surging returned.
I have no codes in the ECU except for when I unplug something.
I am totally running out of ideas/test/things to replace.
The idle timing should be 0 degrees this is set with the computer advance control wire disconnected it is brown with a black stripe; there should be a disconnect inside the factory wire harness that is on the engine it will be on the passenger side of the harness assuming the computer is also on that side of the vehicle as it would be in a production configuration. If you can't find the disconnect you'll need to cut the wire and put a connector in the wire at a place that is convenient.
I'd also remove the power from the battery for a minute or two then reconnect the power this should reboot the computer to resynch its internal clocking.
I would also be aware that the cam may be getting out of time, obviously not many miles sent you installed the engine, but I don't remember if you rebuilt the engine or not.
The symptoms:
1) The idle surges after a cold or cool start.
2) When cold outside and a cold start, it bogs down if you give it throttle.
3) Even when warm, if you floor the accelerator, it pauses and thinks about it.
4) When warm, if you stop and restart, it will only keep running if you give it extra throttle. After time this goes away.
My diagnostics/actions so far:
1) Fuel pressure is 11 PSI at idle.
2) I cleaned the throttle body
3) I removed and cleaned the EGR and checked all of it's lines for clogs and leaks
4) I teased the voltage on the temp sensor and it was 5 (weird number, I thought, but that seems to be what others report seeing)
5) I checked the timing but that's tough because I have a random timing cover on there so the marks are way, way off.
I have photos, I can shoot videos or answer any questions that might help solve this issue(s). And always willing to test out anything.
I had the same symptoms (minus number 4) on my '94 5.7 TBI ... changed EGR, O2, MAP because of CEL codes... symptoms stayed until I changed my TPS. After that, different truck. Replaced with an AC Delco TPS. Read a bunch of forums including this one (which I like the best of all of 'em) and found it wasn't uncommon to get a bad TPS out of the box, most often when an off brand was used or a cheap one was used. Might want to consider changing it out again - I would recommend use a Delco or Delphi.
Also, my new TPS did not come with the little hard, brittle foam-type gasket around the circle where the TPS contacts the TBI. My old one broke in two pieces, but I kinda pieced it together and put it back on very carefully... it works fine.
My timing was retarded 5 degrees... set it to zero the day before I changed the TPS, but that didn't change the high idle nor the surging at idle. That didn't stop until the TPS was swapped out.
I'm pretty much a newbie at this as well, but that's what worked on my truck.
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
Hot Rod Forum
2.2M posts
175.7K members
Since 2001
A forum community dedicated to hot rod owners and enthusiasts. Come join the discussion about restoration, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more!