TBI idle surge

[Warrick]

Hi I have a 88 GMC 5.7 TBI that was running great . I pulled it out and put it in my Chevy van , using a swap loom and a all new fuel system . ever since I started it up it surges at idle and has a misfire when cold and when hot idle is around 1000 rpm . I have been over everything and all looks good . I am getting codes but don't make much sence. Codes are 32 33 34 42 44 45. Any ideas would be great.

[dave w]

Code 32:
EGR open command did not change MAP sensor signal. Normal EGR flow should cause slight decrease in manifold vacuum which would change MAP sensor signal.

Code 33:
MAP sensor signal voltage was too high (low vacuum) for 5 seconds when throttle opening was under 4%.

Code 34:
MAP sensor signal voltage was too low (high vacuum) when engine speed was under 1200 RPM or the engine speed was over 1200 RPM with a throttle position angle above 21%.

Code 42:
The EST signal did not change when the ECM applied bypass voltage to the ignition module.

Code 44:
Oxygen sensor voltage was under 0.2 volts for 50 seconds of closed loop operation. (Lean Exhaust Indicated)

Code 45:
Oxygen sensor voltage was over 0.7 volts for 30 seconds of closed loop operation with a throttle angle between 2% and 20%.(Rich Exhaust Indicated)

I've never experienced a sequence of error codes like this, so I'm only guessing at what the problem / problems are.

Trying the following steps will help remove some / all of the guessing at what wrong.

Maybe the swap loom is for a different engine or computer? Did the swap loom come with a wiring schematic? I know you have been over everything, yet this sequence of errors is SCREAMING wiring problems!! If you don't have the wiring schematics verify pin for pin; what are the voltages going to the MAP sensor, possibly no 5 volt reference? What happens to the signal volts going to computer when a hand vacuum pump is used to "Fake" a vacuum source to the MAP sensor when the ignition key is in the "ON" position / Engine OFF / NOT RUNNING? What is the "Bypass Voltage" when you try to start the engine with the High Volts Wire (the wire that goes from the coil to the distributor) is connected to the coil and the other end of the High Volts Wire is connected to a GROUNDED spark plug instead of being plugged into the distributor cap?

dave w

[Warrick]

Code 32:
EGR open command did not change MAP sensor signal. Normal EGR flow should cause slight decrease in manifold vacuum which would change MAP sensor signal.

Code 33:
MAP sensor signal voltage was too high (low vacuum) for 5 seconds when throttle opening was under 4%.

Code 34:
MAP sensor signal voltage was too low (high vacuum) when engine speed was under 1200 RPM or the engine speed was over 1200 RPM with a throttle position angle above 21%.

Code 42:
The EST signal did not change when the ECM applied bypass voltage to the ignition module.

Code 44:
Oxygen sensor voltage was under 0.2 volts for 50 seconds of closed loop operation. (Lean Exhaust Indicated)

Code 45:
Oxygen sensor voltage was over 0.7 volts for 30 seconds of closed loop operation with a throttle angle between 2% and 20%.(Rich Exhaust Indicated)

I've never experienced a sequence of error codes like this, so I'm only guessing at what the problem / problems are.

Trying the following steps will help remove some / all of the guessing at what wrong.

Maybe the swap loom is for a different engine or computer? Did the swap loom come with a wiring schematic? I know you have been over everything, yet this sequence of errors is SCREAMING wiring problems!! If you don't have the wiring schematics verify pin for pin; what are the voltages going to the MAP sensor, possibly no 5 volt reference? What happens to the signal volts going to computer when a hand vacuum pump is used to "Fake" a vacuum source to the MAP sensor when the ignition key is in the "ON" position / Engine OFF / NOT RUNNING? What is the "Bypass Voltage" when you try to start the engine with the High Volts Wire (the wire that goes from the coil to the distributor) is connected to the coil and the other end of the High Volts Wire is connected to a GROUNDED spark plug instead of being plugged into the distributor cap?

dave w

Thanks Dave yes very strange , I was thinking wiring too I just can't seem to find anything wrong. Wiring did not have schematic just instructions, was all labeled and and quite easy . only wire I have found it doesn't have is the crank signal for starting. I will check out those things you mentioned today. Another strange thing is on hot start up it will idle with timing at 16 deg advanced as should then after about 10 seconds will drop back to 13 ish deg and starts surging, so the hole system is going crazy.

[dave w]

Here is a link for '7747 wiring schematics. http://www.gearhead-efi.com/Fuel-Inj...Information-42

Maybe you have an OHM Meter to verify pin to pin wiring? I know, checking pin to pin is a chore.

I find it very odd an aftermarket '7747 wire harness does not have the crank signal wire.

dave w

[Warrick]

Hi yes I find it strange that wire was missing aswell. According to all the paperwork it is the correct loom. So I went through all the pinouts the other day and the crank signal was the only one missing , so I wired one in, I cleared all the codes again, upon start up was exactially the same , no quicker to start and surged as usual. I gave up for the day and have been driving if for the last couple days and its been running perfectly no surge , haven't been on highway yet but still got up to temp every trip and its been good . now the only code is 34 . I'm not convinced that wire was causing all of that but who knows. Just got to figure out what's causing 34 for now

[Warrick]

So quick update . plugged scan tool in to see if it was any better , it is not . still only code 34 but values are strange like in park at idle says its doing 250 mph , map is like 8inches VAC at .84 volts its all wrong don't even know how its running. So I'm going to have to pull loom off and go through wire by wire to see if anything is in wrong spot.