I’m looking for some help with an engine swap project. I’m transplanting a 1994 5.7/350 from a Suburban into my 1990 Toy rock crawler. The install has been a bit of a challenge but the engine and drive train are in the truck. I’m happy to share the mechanical learning points on this swap with anyone interested.

I have a reasonable amount of mechanical experience but this is my first bout with a fuel injection swap.

The current problem I have is that the engine won’t start. I’ll describe what we have done so far and would appreciate any guidance or hints that may help me get it running.

Facts:

. 5.7/350 TBI engine from a 94 Suburban
. Factory wiring harness in excellent shape
. ECM from same vehicle.
. Engine has spark and will run for a few seconds if primed with gas through throttle body
. Injectors will “pre-spray” for a few seconds but there is no injector spray (pulse) when cranking.
. I have 12v at the injectors.
. Fuel pump is wired to 12v ignition on.
. I have not hooked the Chevy fuel pump relay into the ECM circuit as the in tank Toy pump is wired to 12v ignition on.
. Fuel pressure is 11 psi.
. I have traced every engine circuit from the connections to the ECM and all the wiring is sound.
. I have checked the ignition module and it tested ok.
. I have wired the Toy signals such as 12v constant, 12v ignition and 12v ground into the wiring harness as instructed in the conversion manual. I’m pretty confident the basic circuits are wired correctly
. The battery ground goes to the engine, the engine is grounded to the frame, I ran a separate ground from the ECM “box’ to the engine.
. I have an after market VSS to convert from Toy to GM specs wired in correctly. I’ve double-checked with manufacture to ensure wiring is correct.
. I have not hooked up the knock sensor or the VSC (vehicle spark command) as I plan on not running them.
. Oil pressure cranking is +25PSI

Bits and Pieces:

I have full wiring diagrams from Chevy’s tech computer I got from our local dealer and from Mitchell’s electronic diagnoses software so I can trace and discuss the circuits in detail if need be.

The problem appears to be that we are not getting the ECM to provide the ground pulse to the injectors.

Questions:

Does the fuel pump relay need to be wired into the ECM to make the ECM “think” it has fuel and send a signal to the injectors? Or does the ECM just trigger the relay to turn the fuel pump on?

Following the GM wiring diagram for the oil pressure, fuel relay circuit it appears that line 120 / gray pin number B12 is the fuel pump signal. Does this circuit into the ECM need to be 12v with the ignition on?

Do you need the VCS to make the engine run? Researching the test procedures for the knock sensor and VSC has lead me to believe they are not required to run the engine.

I live on Guam and I don’t have access to a bench ECM tester. I can get my hands on an ECM from a 305 TBI if I need to “try” another ECM. How do I identify if the ECM from the 94 5.7 is compatible with the 5.0 TBI ECM?

The vehicle is a pretty extreme rock crawler, full tube bed, tube doors, coil over suspension, roll cage, 38’s ect., and barley street legal, I’m not striving for a daily driver, street or show vehicle just a cleanly wired, reliable, solid swap. I’m not opposed to tricking the ECM if needed as I don’t need any of the ECM driven accessories.

Any and all assistance will be greatly appreciated.

Fred from Guam

Fuel pump does not have to be wired into the ecm, it doesn;t care if the pump is on.

The oil pressure wire only cuts the power to the pump if oil pressure is lost. I'm running mine without that hooked up

VSS and knock are not required to make it run




The only sensors i have left are the TPS and IAC in the throttle body, coolant temp, MAP, and o2 sensor.

Mine wil run without the o2, coolant temp, and will run crappy without the map but will run.
Start your search at the ignition moduale, they are prone to failure, and they signal the computer to control the timing and trigger the injectors to pulse. If it's faulty it will go into limp mode and still spark, but may not fire the injectors.
I'd also check the voltage drop while cranking, if it's loosing too much voltage while cranking, the computer may not be able to function properly, possibly just from a bad ground.

I can't speak specifically to your ECM
but
On the ECM's that I deal with the fuel pump does need to send the signal back to the ECM. The ECM will turn the fuel pump on for about 3 seconds when the key is initially turned on and will then turn it back on once it has recieved the ignition signal.
(Basics for GM)
red=batt 12V
org=fused 12V
pink/blk= switched 12V
Blk/wht=ground

If you look at this C/K diagram you will see orange fuse 12V coming in on the top going to the FP relay pin A and also over to pin B1 of the ECM, and it sets on one side of the oil pressure sw. This is a constant 12V.

The relay is controlled by the ECM applying 12V to from the ECM pin A1 to pin F of the relay.
The other side of the relay is grounded at pin D.

When the pump turns on the connection is made from pin A to pin E and 12V goes out to several places.
to the fuel pump thru the fuse
to the ECM pin B2 to tell the ECM the pump is on
and to pin A of the fuel module for some models.

So what about the oil pressure sw?

Well noticed it has done nothing up to this point.
But it does have 12V setting on one side of it. Well once the engine develops oil pressure the sw will close and the 12V will be directly applied to the fuel pump.
This is more of a back up for the relay then some kind of safety feature and will not keep the engine from running.
I have cut it out on every swap i have performed.

Now you will need to compare this diagram to yours and trace it out.

http://www.binderbulletin.org/photopost/data/531/1534CK_fuel_pump.jpg

Here's another truck diagram.

http://www.binderbulletin.org/photopost/data/531/1534fuel_pump_wiring-med.jpg

Now also the ECM must recieve the DRP-distr ref pulse in order to provide the ground to fire the injectors.(same as the FP)
Make sure you have good spark while cranking and also verify your voltages for the 12V batt and the 12V sw. I have seen people wire straight to the ignition sw instead of using a relay to power the system and the ignition.
Then you get a huge voltage drop when cranking.
I have also seen people think the used the ignition 12V but will not have 12V during cranking. You must have the proper power and relays.
The pink on the coil and the pink/blk going to the system should all get power from a relay.
The 12V side should be fed from the batt terminal of the starter or the alternator for full voltage.
The wire to energize should come from the ingnition switch that is powered in the start/run position.

Fred,

Sent you an email.

James

You guys must be at Andersen and not Agana!



Here is a link to the diagrams.

Autozone diagrams (http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/08/79/51/0900823d80087951.jsp)

or BIG
http://www.binderbulletin.org/photopost/data/531/153495_GM_truck.gif

or little

http://www.binderbulletin.org/photopost/data/531/153495_GM_truck-med.gif

is only 11lbs. enough fuel pressure? i thought FI was much higher? 30-40ish lbs?

11 will work fine.
I normally set all of mine at 13psi.

TBI operates at a much lower pressure then MPFI.