Ive been working on my pops suburban. It is a 1993 Suburban 4x4 350 tbi.
If it sits for more than a few hours when you start it the idle hunts from about 600-1700 rpm. It will spit fuel out of the tail pipe. It will die occasionally but most of the time it manages to stay running. If you rev it up it seems to run fine, but when it idles back down it starts again. If you. After about 40 seconds to a minute it runs perfectly fine.
If you unplug the timing bypass it seems to run fine.
I had an injector leaking down on an old car and after starting it, you could rev it hard and clear it out, and then it would be fine. The burb doesnt do that, it smooths out when revved but goes back to running poorly when it comes back to idle.
Things Ive done
Fuel pump and filter. It died about 6 months ago. Probably started a few months after that. Fuel pressure is still good.
New ECT sensor. yes it was the one on the intake not the head.
New IAC. Used to randomly die at idle when warm. Doesnt seem to do that anymore
TBI rebuild. Did with fuel pump preventatively
New distributor, then I heard the new parts house distributors can cause this so I grabbed a reman and stuck a GM module in it, with a new cap and rotor. No change.
Checked timing. Yes I pulled the bypass to set it.
Tried smoking the intake, dont have a good way to seal the TBI, so I went old school and tried carb cleaner all over the intake, including the front and rear. No response from engine.
Checked vacuum, its 19-20 inHg at idle
I thought maybe my balancer (and timing mark) had slipped and so I was unknowingly setting the timing wrong, I verified with 1 at TDC, timing mark is were it belongs.
Injector spray pattern looks good. I watched the injectors for a few minutes after turning truck off, saw no drips.
I can datalog with Tuner Pro RT. I was looking at data this morning. Map sensor seems to fluctuate between 35-50 kpa when idle is freaking out, but stabilized at about 35 kpa when idle calmed down. Map readings respond to throttle input quickly and will run up to 100kpa with WOT.
TPS is smooth all the way through the range
INT is 128
BLM is 125
The only thing that really stuck out at me on the log was knock retard. I cant hear any pinging or engine noise, but it is showing 26.2 degrees of KR. It does move but only to 26.4. it will periodically move from .2 to .4. I unhooked the battery and touched the cable and wanted to see if KR build slowly, but as soon as i started it 26.2. I dont know if this is a real PID or not, I have a couple of data points on Tuner Pro that dont exist. I unplugged the knock sensor and still showing 26.2 or .4 on KR.
Any recommendations or places to start?
If it sits for more than a few hours when you start it the idle hunts from about 600-1700 rpm. It will spit fuel out of the tail pipe. It will die occasionally but most of the time it manages to stay running. If you rev it up it seems to run fine, but when it idles back down it starts again. If you. After about 40 seconds to a minute it runs perfectly fine.
If you unplug the timing bypass it seems to run fine.
I had an injector leaking down on an old car and after starting it, you could rev it hard and clear it out, and then it would be fine. The burb doesnt do that, it smooths out when revved but goes back to running poorly when it comes back to idle.
Things Ive done
Fuel pump and filter. It died about 6 months ago. Probably started a few months after that. Fuel pressure is still good.
New ECT sensor. yes it was the one on the intake not the head.
New IAC. Used to randomly die at idle when warm. Doesnt seem to do that anymore
TBI rebuild. Did with fuel pump preventatively
New distributor, then I heard the new parts house distributors can cause this so I grabbed a reman and stuck a GM module in it, with a new cap and rotor. No change.
Checked timing. Yes I pulled the bypass to set it.
Tried smoking the intake, dont have a good way to seal the TBI, so I went old school and tried carb cleaner all over the intake, including the front and rear. No response from engine.
Checked vacuum, its 19-20 inHg at idle
I thought maybe my balancer (and timing mark) had slipped and so I was unknowingly setting the timing wrong, I verified with 1 at TDC, timing mark is were it belongs.
Injector spray pattern looks good. I watched the injectors for a few minutes after turning truck off, saw no drips.
I can datalog with Tuner Pro RT. I was looking at data this morning. Map sensor seems to fluctuate between 35-50 kpa when idle is freaking out, but stabilized at about 35 kpa when idle calmed down. Map readings respond to throttle input quickly and will run up to 100kpa with WOT.
TPS is smooth all the way through the range
INT is 128
BLM is 125
The only thing that really stuck out at me on the log was knock retard. I cant hear any pinging or engine noise, but it is showing 26.2 degrees of KR. It does move but only to 26.4. it will periodically move from .2 to .4. I unhooked the battery and touched the cable and wanted to see if KR build slowly, but as soon as i started it 26.2. I dont know if this is a real PID or not, I have a couple of data points on Tuner Pro that dont exist. I unplugged the knock sensor and still showing 26.2 or .4 on KR.
Any recommendations or places to start?
