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.
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
Originally Posted by 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
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.
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
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
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.
Are you using a Vehicle Speed Sensor?
dave w
Yep the standard one out of original pickup using pickup transmission aswell , so nothing has been changed.
I am curious, is there Vehicle Speed Sensor Buffer (VSSB). I've been thinking maybe the aftermarket harness might not have wiring for a VSSB? I doubt not have a VSSB or VSS is causing the codes you are experiencing. Just checking to see the computer is getting a vehicle speed signal.
dave w
I don't think it has vssb I haven't seen one or anything about one. It is getting a signal to ecm its just 250 mph ish in park but unplug it and goes to 0 .
Has either of the original chips come loose in the ecm? Was either of the chips removed for any reason?
Routing speed sensor wires near spark plugs or coils can create a varying voltage which the ecm interprets as speed. How is the harness to the speed sensor routed? Vans with TBI used fairly long harnesses.
High MAP codes can be set when the ecm has the IAC fully opened in an attempt to keep the engine idling. You will often hear the a very different sound, possibly a whistle, if the IAC is fully opened at idle. High RPM can occur if there are vacuum leaks. Multiple MAP codes can be set if the wiring harness is routed to closely to spark plug wires or coil.
High and low O2 codes can also be set simultaneously if the wiring is too close to a secondary side ignition component.
A quick and easy check might be to compare scantool readings with engine idling against readings when key is on and engine is off.
Also, silly question, what are you using for a scantool? What are you selecting for a vehicle when you connect the tool.
Hi I never removed any of the chips from ecm .
My harness goes from behind engine to bellhousing area , tranz wires go back and engine wires go forward . I pretty confident none are near any ignition stuff, I will check it out though.
Have done scantool readings running and not to compare . things are crazy in both . here's a couple I remember off hand. Engine off map is sitting at 25 inhg and 4.6 v running 8inhg .8 v , but with VAC gauge its 16 -17 inhg. o2 sensor sits at 4 off with a consistent spike to 450 ish in a pattern dono if that's normal? When running values look OK and switches as should. Speed way wrong . tps looked correct . temp looked good . think the IAC was reading 69 from memory at idle , but was idling around 1000 rpm. a few other things that were a bit off aswell. Got to be a common problem somewhere. Was using a snapon scantool , selected 88 GMC c 5.7 pickup that's what it is all out of.
Warrick
Sounds like most everything's covered. I might open the cover on the ecm just to make sure "what I know" is true... that chips didn't get knocked out during swap.
Ground problems can cause some very strange readings. Is the engine to battery ground intact? Engine to frame? We have a fleet of vans and we used to see some really strange readings when the ground straps from the back of the engine to the body rotted away. You probably did this but make sure new wiring harness grounds are all attached, too.
Just trying to hit all the "gotcha's."
Been through all the wiring all looks good . where does the vss wiring go to? as I'm not running a instrument cluster, and still getting 250 mph in park. Also my map vaccum is backwards is 25 inhg 4.1 v not running but at 8inhg 1v when running , what's up with that?
I seem to have fixed the surge that is not happening now . main issues now are information on scan tool is all backwards and wrong, and idle will not go below 1000 rpm, IAC won't let it. I have a spare set of all sensors and ECU they are all doing the same thing . any ideas??? Oh and I have no codes now, even after a drive down highway.
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