350 TBI Boggs and surges under load

[sntrym]

Which temp sender did you check? There are two - one in the head that goes to the gauge and one in the intake that goes to the ECM.

 

[Sean Buick 76]

A real scanner will tell
You what’s going on. Pay a shop to test or buy a unit

 

[Road Trip]

Knew I forgot something. No Codes, even if I try to force the issue.
Don't have a scanner. I don't know where to get one, You need a laptop right?

I watched your videos, and in the 'Interior' video, were you jumpered
while your engine was running and therefore in 'Field Service' mode?

If so, I thought I read that if you are jumpered while running that the
ability to store codes is temporarily disabled? If so, then please shut
down, removed the jumper, start back up, stimulate the fault, and if
the light now comes on steady, then shut down again...and now
jumper A & B together, perform the KOEO (Key ON Engine OFF)
step, and see if you now get some codes to display?

EDIT: I just rewatched your video, and this time I caught your
question about the flashing SES light. As a matter of fact, yes,
if you are jumpered while running the light is working in a completely
different mode. With the key off, please remove the jumper,
fire up, and see if you can't stimulate the fault & get the SES light
to come steady illuminated. If you are able to make that happen, you should end
up with retrievable codes by following the instructions in the previous
paragraph.

Good luck --

 

[Madcrafter52]

Which temp sender did you check? There are two - one in the head that goes to the gauge and one in the intake that goes to the ECM.

Tested the ECM one and it checks out. The gauge one is busted.

A real scanner will tell you what’s going on. Pay a shop to test or buy a unit

Yeah I think I'm gonna buy a ALDL cable and use my laptop. But its such a pain to get anything in Canada

I watched your videos, and in the 'Interior' video, were you jumped
while your engine was running and therefore in 'Field Service' mode?

I have tried it both ways with the same result

Anybody know what this white box is? it has one open connecter.

You must be registered for see images attach

 

[sntrym]

That's your VSSB. It does speed conversion from the VSS for the speedometer. More info here: https://harristuning.com/Tbi/vssb-drac-calibration/

 

[Madcrafter52]

So something weird happened. I disconnected the timing advance and set the timing where it was happy, probably about 15 degrees advanced. ran nice and smooth, no surging. Figured this meant there was an issue with the timing advance. Set it back to 0 degrees and plugged the advance back in. Now the surging is gone, like completely gone. Decided to take it for a drive and its pretty smooth, just no power. If I flatfoot it the truck struggles to get to 50kmh and wont go over 3500 rpm. Also the TBI makes a super loud sucking noise, almost sounds like its gasping for fuel. Once I parked, again no codes, and the vacuum is low at only about 18 inches. Imo the truck feels like it is not getting enough fuel or timing as when I had the timing locked in manually the vacuum was around 22 inches. Anyone know what would cause this

(I also have an ALDL cable on the way)

 

[Road Trip]

So something weird happened. I disconnected the timing advance and set the timing where it was happy, probably about 15 degrees advanced. ran nice and smooth, no surging. Figured this meant there was an issue with the timing advance. Set it back to 0 degrees and plugged the advance back in. Now the surging is gone, like completely gone. Decided to take it for a drive and its pretty smooth, just no power.

Alright, I like the fact that you temporarily bypassed the computer generated spark timing and
set it manually to where it was happy. I then went through your list, and did not see anything
about the Knock Sensor? I also went back to reply #10 and listened carefully to the 'engine bay'
video, and I heard a steady knocking sound in the background, loudest when you had the camera
over the left bank? Do you know the source of that sound? And is it possible that the Knock Sensor
is picking up that sound, and in turn the computer is pulling timing out, causing at least part of the
symptoms that you are experiencing?

To prove/disprove this, it would be interesting to temporarily disconnect the knock sensor and
see what difference in running, if anything, happens?

If I flatfoot it the truck struggles to get to 50kmh and wont go over 3500 rpm. Also the TBI makes a super loud sucking noise, almost sounds like its gasping for fuel. Once I parked, again no codes, and the vacuum is low at only about 18 inches. Imo the truck feels like it is not getting enough fuel or timing as when I had the timing locked in manually the vacuum was around 22 inches. Anyone know what would cause this

(I also have an ALDL cable on the way)

Glad to hear about the cable. In order to come up with some additional troubleshooting ideas
between now and when the cable arrives, I went back to the other video in reply #10 ('interior')
and attempted to translate what the Field Service mode flashing light was communicating to us.
Here I've attempted to graph out the 3 (of 4) different modes it reported:

You must be registered for see images attach

So instead of the SES light flashing randomly, it actually shared some useful hints. (Of course this is no substitute for live data, but
since this is here and the ALDL adapter is on it's way, why not take a peek?)

What I found interesting was that initially your system was able to go into a steady 50/50 duty cycle
Closed Loop from the :03 to :12 mark, so it's possible. Even more interesting is it looked like while you
were trying to depress the gas pedal at around the :18 second mark the system went *rich* and stayed that way
all the way to the 33-second mark. And the system never reported a lean condition?

Based upon everything I've read in this thread, my first reaction to the above is that you
are suffering from a 'False Lean' condition. In other words, you are experiencing a misfire
where the intake charge is never consumed because of a missing combustion, so that
oxygen exits during the exhaust stroke, past the O2 sensor, which reports what it sees
up to the computer, which in turn starts commanding a richer mixture to compensate.

Of course this is just theory based upon listening to how the engine is running and
watching what the ECM is reporting in Field Service mode, but given the amount of effort
that you've put into the Ignition and Fuel delivery systems, I think we have a direction
to go in.

I reviewed your list of parts in reply #1. I may have missed it, but I don't see anything
about the EGR valve or the Knock Sensor? I'm not too worried about the fuel delivery
or quantity of spark, but a leaky or out of control EGR will certainly create a misfire condition,
especially at low throttle angles. And a Knock Sensor responding to a noise in the engine
(or an overly sensitive KS on a quiet engine) can certainly pull out too much timing and
also negatively affect the engine performance.

Trying to learn a little more of the history of this truck (ie: when was the last time that
it ran correctly?) I found your original post: (Truck bought with swapped motor for the right price.)

In the land of internal combustion, the 3 absolutes of quality combustion is good
Spark, Fuel, and Compression. I might of missed it, but I didn't see any mention of
a compression test, leakdown test, or valve preload check? Have you pulled the spark
plugs and given them a careful visual inspection?

****

This is already longer than I wanted it to be, so I'll stop here and await for your
response. Based on everything above, I would try to find out about the following:

* What is that knocking sound over the driver's side valve cover?
* What is the condition of the EGR valve?
* What is the condition of the Knock Sensor?

If nothing obvious, then continue to:

* Pull the plugs, and compare each one against the other 7. Are they all the same,
good color? Or do you have 1 or more outliers?
* While the plugs are out, run a careful compression test. (Fuel injector fuse pulled,
Ignition fuse pulled, throttle held open, fresh battery, all plugs out, crank each cylinder
for 5 compression strokes, write down the results for each cylinder, and share the results.

We'll save the leakdown check discussion for whether or not it's warranted based upon
the results of the compression test.

Note: You may end up pulling the left valve cover in the hunt for the source of the knock
heard in the video. If you do, then take a look at all the rocker arm adjusting nuts and
see how close the thread count is to each other. (ie: Trying to figure out if the PO had good
or bad luck with adjusting the valve lash.)

Again, all of the above is based on the way that the engine is running despite a full conventional
tune up & renewal of the fuel delivery subsystem. And getting a handle on all this
will only set you up for success once the new data cable arrives.

I'm interested in whatever you discover.

Best of luck --

 

[Road Trip]

Decided to take it for a drive and its pretty smooth, just no power. If I flatfoot it the truck struggles to get to 50kmh and wont go over 3500 rpm.

Also the TBI makes a super loud sucking noise, almost sounds like its gasping for fuel. Once I parked, again no codes, and the vacuum is low at only about 18 inches. Imo the truck feels like it is not getting enough fuel or timing as when I had the timing locked in manually the vacuum was around 22 inches. Anyone know what would cause this

(I also have an ALDL cable on the way)

Hello again Madcrafter52,

Since writing reply #17 yesterday I've been thinking a little more about your situation.

Q: What kind of exhaust do you have on this truck? Is it possible that before/during/after
the engine swap the PO managed to partially melt the honeycomb in the cats and the engine
can only force so much exhaust through them before they act as a bottleneck? This can
manifest itself in a couple of different ways. For example, the older EGR valve design didn't
take into account exhaust backpressure, so with a (partially) plugged exhaust when they
opened, a lot more inert, non-combustible gas was metered than expected, causing rough
running/drivability issues on an otherwise healthy engine?

Not to mention not being able to get the engine above a certain airflow, manifesting as
not wanted to climb above a certain rpm?

If you had 2 upstream O2 sensors then you could temporarily remove them both and see
if you can detect any difference in engine behavior. (Open loop of course, but would still tell
you something.) But (I think) that since you only have a single O2 sensor you are going to
have to temporarily disconnect the exhaust (bungee cord to the frame or similar) and
take a quick test drive to prove/disprove the theory.

NOTE: A little more elegant approach would be to remove the O2 sensor and thread in a
exhaust backpressure PSI gauge with a long hose & tape that to your windshield so you
can monitor it while the engine is accelerating, and since your O2 sensor has been recently
changed it shouldn't be too hard. (See attached - Pro OTC gauge vs Hobbyist level gauge.)

Definitely your call. Some prefer to disconnect the exhaust, others prefer the gauge. But
either way, if removing the exhaust makes the engine run right, then you know where you
need to go. And if it *doesn't* make a change in the way your engine runs, then we know
that we've still got to figure out what's up with the 'ex-TPI former Camaro engine' that
the PO installed in your truck.

This is an interesting problem. Looking forward to your next update.

Best of luck --

 

[Madcrafter52]

Trying to learn a little more of the history of this truck (ie: when was the last time that
it ran correctly?) I found your original post: (Truck bought with swapped motor for the right price.)

I know nothing about the history of the truck and have no contact with the guy I bought it from. I just know it started life with another 350 TBI and after experiencing the same issues the last guys decided to swap the engine for some reason. (talk about fix by wallet) It now has a 350 out of a same year Camaro (Roller cam then?) with all the TBI stuff swapped over in place of the TPI. So honestly this doesn't seem like it has anything to do with the engine itself.

* What is that knocking sound over the driver's side valve cover?
* What is the condition of the EGR valve?
* What is the condition of the Knock Sensor?

Not sure where that noise is coming from. Ill try and track it down
I haven't touched the EGR or Knock sensors yet. I know you can test the EGR with a vacuum pump but I don't have one. Any other way of testing? As for the Knock sensor will just unplugging it take it out of the equation for now? (aside from the check engine light) or will it cause other issues?

* Pull the plugs, and compare each one against the other 7. Are they all the same,
good color? Or do you have 1 or more outliers?

I did the plugs when I first got the truck. The ones I took out were almost brand new so I still have them. All the same, good colour.

* While the plugs are out, run a careful compression test. (Fuel injector fuse pulled,
Ignition fuse pulled, throttle held open, fresh battery, all plugs out, crank each cylinder
for 5 compression strokes, write down the results for each cylinder, and share the results.

I just got a compression tester today so I will run the test when I have the chance

Q: What kind of exhaust do you have on this truck?

Its got an aftermarket side exit on it. No cats only a Flowmaster muffler. 02 sensor is still in the original spot. So most likely not a exhaust restriction.

Something interesting I found out from the RPO codes is that this is a Z71 truck. I never knew because someone removed all the decals on the truck, I've got replacements on the way!

BTW thank you so much for all this help Road Trip and everyone else. This has been a huge learning curve for me. Maybe when it stops pouring rain outside I can get some more work done on the truck

 

[Madcrafter52]

couple updates:

I tested the EGR valve with a vacuum pump and it was bad so I replaced that. Now the vacuum seems higher at idle

I also replaced the temp sensor but the gauge still doesn't work for some reason. If I ground the sensor wire the gauge goes all the way up so its not a wiring issue. The body of the sensor is well grounded so idk.

But best of all I got my ALDL cable!!!

I somehow managed to figure out Tunerpro RT and took a data log as attached. I didn't know how long to make it or what to do during it so its pretty short and is just me chugging the engine. maybe someone can make heads or tails of what's going on.

If you need anything else let me know!