Farm truck refresh

[MTCK]

Nice you are getting after it.

[Mavis79]

Front half of the frame painted, replacement cab on, engine/trans mounted

[Mavis79]

Engine turns over, now I have to finish the TBI/4L80e swap...any tips on the speedometer? Can a digital speedo from an r/v be easily swapped into this dash (wiring wise)?

[MTCK]

Looking real good. The gauge clusters look the same on my 91 as the older trucks. You'll need the proper DRAC for your gear ratio and tire height as well.

[Mavis79]

Got everything wired in except for the speedometer. I crossed my fingers and tried to start the truck...only to find I'm not getting any fuel out of the injectors. Tested the fuel feed line after the filter and the pump is putting out fuel. Cracked the feed line at the TB...getting fuel there too. Pulled the return line at the tank and only got a few drops even while cranking...

My thoughts are either a bad pressure regulator or a weak pump. How do you test the pump pressure? My old ford had a Schroeder valve.

[MTCK]

Did you put a new pump in when you modified the sending unit on your old tank?

[Mavis79]

No, it's the pump from the donor truck...

[Mavis79]

Well, swapped pumps and no change...so the possibilities are:

1. Both pumps work, but do not produce enough pressure (I would think this is highly unlikely).

2. The Fuel pressure regulator is bad (however, I have not seen the fuel return to the tank, this seems to suggest not enough pressure).

3. Bad ECM (i.e. the ECM is not telling the injectors to "fire")

4. Clogged Injectors

Any other ideas/possibilities?

[Mavis79]

Just about ready to swap intakes, slap on a carb and go back to the TH400 Trans....

[MTCK]

I agree two bad pumps is unlikely. The trickle of fuel doesn't sound right. I have gotten in the habit of double and triple checking all my grounds in a situation like this. That has bitten me before. Also are you using the jumper for testing at the fuel pump relay or just cycling the key? Pumps making healthy noise? Is your gauge behaving correctly or pointed at 3:00? I'll try to think of some more things to check.

[daddyjeep]

So, you are getting some amount of fuel pressure to the TB. The fuel is not coming out of the injectors or going back the return line. Seems to me that something is blocked up. I'm no expert on Throttle Bodies mind you, I'm just throwing out ideas. It is possible that the injectors are not firing, but if they are not the fuel should get returned back to the tank. It would be nice if you had a way to measure the fuel pressure too.

[MTCK]

http://67-72chevytrucks.com/vboard/s...light=tbi+swap

This thread is really long, but I found some great info when I swapped the TBI onto my 77 K10 in here. Lots of troubleshooting ideas.

[Mavis79]

MTCK, I am cycling the key. I can hear the pumps run, and on the first pump discontented the fuel line after the filter to ensure flow. Once I verified flow past the filter, I "cracked" the line at the throttle body and verified flow to the TB (although it is all new lines/filter).

I'm not sure I can jump the pump relay...I haven't really looked into it as I have verified the pumps run when the key is cycled. Could the relay be the cause even though the pumps are running?

I haven't hooked the gauge up yet...as I put in a "new" drivers side tank. I only had a passenger side before...and will eventually have dual tanks. I will be running a single drivers side tank for now....

I'll look through your thread...Thanks for the help, as usual you are an excellent source of knowledge...

DaddyJeep, I agree...my first thought is a plugged FPR...but like you I'm not an expert on the TB's...yet...I think I'll be very well versed by the time this is fixed....

[MTCK]

If you have a stock style fuel pump relay, there is a single red wire coming out the bottom of the housing. Put 12+ there and pump should run continuous. Could help with trouble shooting.

[Mavis79]

Well looks like I'm not getting a pulse signal to the injectors (at least as best as I can tell).

[Mavis79]

Got a noid light to test the injector pulse and confirmed that is the problem. I guess that means my ECM is bad...

Harness is a new swap harness, ECM has power as confirmed by the check engine light.

[daddyjeep]

the injectors pulse so fast that you really can't verify if you are getting the electrical pulse without a noid light as previously mentioned.

[Mavis79]

After doing more reading I see that the injectors won't pulse unless there is spark. I'll start chasing the spark side and see where that leads...