**FIXED!!**DEFINITELY***Super HIGH idle after multiple parts replacement - TBI 1990 K1500 350engine

[Blue85]

When you say MAP disconnected, do you mean the vacuum hose or the electrical connector? No vacuum to the MAP is basically the same thing as WOT, which you would expect to be way more fuel, but I don't know what an OBDI ECM does with 700 RPM, TPS ~0 and MAP ~0 (this isn't a real-world operating condition). If you are unplugging the electrical, the ECM will see the signal out of range and ignore it.

When you get a scan tool, it will tell you if it's rich or lean. If the surging is due to lean conditions at idle (fuel trims are maxxed positive), but more reasonable values under load/higher RPM, that points to a vacuum leak. If it's rich at idle, that suggests a sticking injector or maybe a bad MAP sensor. If it's trimming positive in most regions, that points to low fuel pressure. If they won't sit at zero, it's safer for the LTFT to be a little negative than a little positive. Remember that fuel trim "STFT", "LTFT" (assuming TBI has both of these) is not a single number. It's a table with different values at different RPM and MAP.

A couple more basic things. Have you verified the timing is correct with a timing light? Have you measured the actual manifold vacuum while it's idling?

 

[ZombieK5]

It should hold pressure. I don't know as there is a spec, but GM programmed the ECM to only prime every ~15 seconds (via the ignition being cycled with the key) so they must have thought it should hold for at least that long. I had a split hose in the tank (from ethanol, known problem with old hose that wasn't rated for it) and it would build pressure and immediately drop. New hose shouldn't have that issue. But if so, problem normally lessens on a full tank.

IMO with that low of pressure when running, hard starts, and running smooth on fuel tables that are richer than what it normally would be (MAP disconnected) it indicates a potential fuel issue.

It idles better cold too, yes?

It DOES NOT idle better cold. Surges almost immediately.

My data cable came in yesterday. I need to setup TunerPro then I'll get some readings.

I need to back the truck out of the garage so I can start fixing the rotted frame on stepson's 2014 Silverado.

 

[ZombieK5]

When you say MAP disconnected, do you mean the vacuum hose or the electrical connector? No vacuum to the MAP is basically the same thing as WOT, which you would expect to be way more fuel, but I don't know what an OBDI ECM does with 700 RPM, TPS ~0 and MAP ~0 (this isn't a real-world operating condition). If you are unplugging the electrical, the ECM will see the signal out of range and ignore it.

When you get a scan tool, it will tell you if it's rich or lean. If the surging is due to lean conditions at idle (fuel trims are maxxed positive), but more reasonable values under load/higher RPM, that points to a vacuum leak. If it's rich at idle, that suggests a sticking injector or maybe a bad MAP sensor. If it's trimming positive in most regions, that points to low fuel pressure. If they won't sit at zero, it's safer for the LTFT to be a little negative than a little positive. Remember that fuel trim "STFT", "LTFT" (assuming TBI has both of these) is not a single number. It's a table with different values at different RPM and MAP.

A couple more basic things. Have you verified the timing is correct with a timing light? Have you measured the actual manifold vacuum while it's idling?

I am assuming that this image shows the actual manifold vacuum. This was when I disconnected the EGR vacuum tube at the tbi. Shows a pretty serious vacuum if you ask me. The timing seems to be perfectly fine. When I say I disconnected the map sensor I mean I pulled out the electrical connector the left of vacuum hose in place. With that out of place the engine runs smooth as glass. Which to me suggests timing is fine. Also, since I removed the TBI and replaced all the gaskets and injectors, I didn't touch the timing on the truck. The truck timing was fine before I started the work. No, I have not actually checked it to confirm, I am basing this on the truck running fine before I started the work. If needed I can pull out my timing light, dust it off because I haven't touched it in 30 years, and see if I can get a reading on it.

 

[folkenheath]

I am assuming that this image shows the actual manifold vacuum. This was when I disconnected the EGR vacuum tube at the tbi. Shows a pretty serious vacuum if you ask me. The timing seems to be perfectly fine. When I say I disconnected the map sensor I mean I pulled out the electrical connector the left of vacuum hose in place. With that out of place the engine runs smooth as glass. Which to me suggests timing is fine. Also, since I removed the TBI and replaced all the gaskets and injectors, I didn't touch the timing on the truck. The truck timing was fine before I started the work. No, I have not actually checked it to confirm, I am basing this on the truck running fine before I started the work. If needed I can pull out my timing light, dust it off because I haven't touched it in 30 years, and see if I can get a reading on it.

View attachment 503968

Does it hold steady or fluctuate?

I think the fact that it goes wonky when you unplug the MAP connector that likely means its getting bad data from somewhere and its ignoring it when it doesn't have the data it needs to calculate. You just need to figure out where.

 

[ZombieK5]

Exactly. I can't figure thay out. MAP should be fine, I'm in the 2nd NEW sensor. TPS should be fine. What does that leave?

IAC
Spark Control
Computer
EGR Solenoid (but it surges in closed loop)
Fuel Pump (but it holds at 10psi)
O2 sensor (but it surges in closed loop)
Water Temp Sensor (new installed and unlikely to cause issue)

I am going to get the data cable connected to the laptop and the truck and see what happens. I specifically want to see what the IAC count is. For my understanding should be between 10 and 15. I'm going to try using TunerPro or WinALDL

Does it hold steady or fluctuate?

Vacuum holds steady

 

[gmbellew]

Might try unplugging the O2 to force it to stay in open loop and see if that stops the surging. Leave the MAP plugged in. Loss of MAP data puts it in a safe mode on fueling. Loss of O2 should just keep it in open loop, I think.

IAC anywhere under 30 or so, when fully warmed up, should be ok at idle with no AC on.

 

[ZombieK5]

Might try unplugging the O2 to force it to stay in open loop and see if that stops the surging. Leave the MAP plugged in. Loss of MAP data puts it in a safe mode on fueling. Loss of O2 should just keep it in open loop, I think.

IAC anywhere under 30 or so, when fully warmed up, should be ok at idle with no AC on.

I will definitely try that today when I get home from work. I am working on getting the aldl software set up on my laptop. I'm getting the parameters downloaded now

 

[ZombieK5]

Might try unplugging the O2 to force it to stay in open loop and see if that stops the surging. Leave the MAP plugged in. Loss of MAP data puts it in a safe mode on fueling. Loss of O2 should just keep it in open loop, I think.

I unplugged the O2 after engine warmed up and the surging continued. ALSO, wierd.... I unplugged the O2 sensor and the ALDL Scanner kept reading voltage under the O2. Cant explain that. Would the O2 wire be shorted out somewhere?? I am guessing that the SINGLE WIRE lead for the O2 is a positive wire that measures the O2 resistance??? Should the O2 still read voltage if it is unhooked??

 

[ZombieK5]

IAC anywhere under 30 or so, when fully warmed up, should be ok at idle with no AC on.

IAC for cold engine read 145

IAC after engine was warm and the O2 sensor read closed read 94 with coolant at 169 and IAC read 60 with coolant at 188

 

[ZombieK5]

When you say MAP disconnected, do you mean the vacuum hose or the electrical connector? No vacuum to the MAP is basically the same thing as WOT, which you would expect to be way more fuel, but I don't know what an OBDI ECM does with 700 RPM, TPS ~0 and MAP ~0 (this isn't a real-world operating condition). If you are unplugging the electrical, the ECM will see the signal out of range and ignore it.

When you get a scan tool, it will tell you if it's rich or lean. If the surging is due to lean conditions at idle (fuel trims are maxxed positive), but more reasonable values under load/higher RPM, that points to a vacuum leak. If it's rich at idle, that suggests a sticking injector or maybe a bad MAP sensor. If it's trimming positive in most regions, that points to low fuel pressure. If they won't sit at zero, it's safer for the LTFT to be a little negative than a little positive. Remember that fuel trim "STFT", "LTFT" (assuming TBI has both of these) is not a single number. It's a table with different values at different RPM and MAP.

A couple more basic things. Have you verified the timing is correct with a timing light? Have you measured the actual manifold vacuum while it's idling?

TWO Videos showing the active running numbers for the truck.

FIRST video is from a cold start.
SECOND video is after the O2 opened.

The O2 was all over the place when warm

Something strange. I disconnected the O2 after the engine was warm and the scanner still showed VOLTAGE for the O2. What is that about.

The IAC numbers may be high.

ERRORS
The scanner showed two errors.

34 - MAP Low
44 - Oxygen Sensor Lean

The O2 sensor error did not show up until the engine started warming upl

View attachment ALDL Cold 2.mp4

View attachment ALDL 2 Warm.mp4

 

[Wes Harden]

The o2 is supposed to switch above and below .5mv constantly. This is how the computer knows the fuel changes it calculates are working. Also that the information from other sensors is accurate.

If you still see voltage on the o2 unplugged you have a wiring issue. the o2 circuit might be shorted to power some where

 

[ZombieK5]

The o2 is supposed to switch above and below .5mv constantly. This is how the computer knows the fuel changes it calculates are working. Also that the information from other sensors is accurate.

If you still see voltage on the o2 unplugged you have a wiring issue. the o2 circuit might be shorted to power some where

Diagram shows the 02 is wired directly into the ECM through the firewall. I will pull the wire out and see if it is compromised. It is a short distance from the O2 pigtail to the ECM so it should be fairly easy to trace.

I am not sure what the low voltage on the MAP sensor means or what would cause that. The MAP sensor is wired directly to the two ECM Modules along with the 416.8 Gray wire from the TPS that is tied into the MAP Sensor wire with the same identification number. Any MAP issues would come from the ECM or a faulty switch. The sensor in the truck is the 2nd new sensor

 

[Wes Harden]

I would expect low map sensor voltage if it had been unplugged, unless codes had been cleared.

With all the plugging and unplugging of sensors and actuators, I wouldn't be surprised if terminals were a bit loose and not making good contact.

 

[Blue85]

A few things jump out. First, why do you have knock counts? 2nd, O2 should read a fixed voltage when it's unplugged. When the engine and sensor are operating correctly, O2 should bounce continuously between 0 and 1V (approx), like once a second or so. It's the crossing of 0.5V that tells the ECM you've hit stoich.

FYI, O2 sensor is not a resistor, it's more like a battery. When hot, it generates a voltage, but supplies virtually no current. This means the ECM has high-impedance, which lets it kind of float when no sensor is detected.

 

[ZombieK5]

I would expect low map sensor voltage if it had been unplugged, unless codes had been cleared.

With all the plugging and unplugging of sensors and actuators, I wouldn't be surprised if terminals were a bit loose and not making good contact.

OK, makes sense. Plan for tomorrow is

1. Trace O2 sensor wire for shorts
2. Clear codes (disconnect neg cable)

Connect laptop and get new set of readings

 

[Wes Harden]

should be able to clear codes with scan tool.

 

[gmbellew]

IAC is too high. first, id jumper AB on the ALDL and turn key to ON for 30 sec or so. turn key off, remove jumper, see if that lowers the counts. if not, you may need to adjust the min idle air screw to get more air passing through the blades. looking at your TPS voltage, you will need to bend the tab to bring the volts back above 0.5 after you make the screw adjustment.

 

[gmbellew]

the codes are stored for 30 starts. so those are likely just from you unplugging things. they will eventually go away, or disconnect the negative terminal for a bit.

 

[Blue85]

BLM = Block Learn Management, later known as LTFT. INT = Integrator, later known as STFT. In the screen shots, yours are at/near 128, which is the equivalent of 0% for OBDII. In the first screen shot, that's just because Loop Status = OPEN. In the 2nd screen shot, it says BLM Learn = OFF, but why? Coolant temp is OK. Maybe because TPS is below minimum? It's interesting to see that under the open loop conditions the ECM is logging O2 cross counts. That's either noise in the signal or the AFR is measuring near stoich.

In the 2nd video, IAC is changing, presumably trying to fix the idle speed. However, the idle speed is also rolling in the first video, while IAC doesn't move. This means either timing or pulsewidth is changing to cause the rolling idle.

Update rate to the display is slow, but the O2 numbers we see are mostly <0.5V, implying that if anything, the mixture is lean. Your error/DTC for lean condition could be current and it could be history, from before you were fixing vacuum leaks.

 

[Blue85]

Also, the vacuum numbers all seem a little bit low (like maybe there is a vacuum leak). Your manual gauge says 19 (was idle rolling during that measurement?), but in the videos it's going from 9-19 as the engine is hunting for idle. I would almost expect 21+ as the engine decels from 1200 to 800RPM.

I guess it's worth noting that a lean error can come from a vacuum leak, low fuel delivery or an exhaust leak.