Re: Tbi swap build thread
 

Hi Mark

I went a surge tank setup after reading conversion problems experienced by folks with non EFI tanks. Since our trucks are equipped with long saddle tanks fuel sloshing under low fuel levels can result in fuel sock aeration. When this happen fuel pump may experience instantaneous fuel cavitation resulting in fuel pressure loss and possibly inlet vapor lock. In other words - not good. Jeep guys face this problem all the time, but they have it easy by retrofitting to EFI tanks which incorporate fuel baffles to keep fuel sock covered under extreme angles. Alternatively, a small surge tank with low pressure lift pump is a workable solution. Noted, that this is not cheap nor is it simple to implement. There are couple advantages to surge tank system one being use of low pressure lift pump which can be conveniently mounted which can not be done with high pressure EFI pumps. Typically, low pressure lift pumps are self priming, so that if fuel sock aeration does take place pump re-primes itself while EFI pump keeps on delivering un-interrupted fuel flow to injectors. Low pressure pump fuel delivery can take awhile depending on fuel sloshing which plays into surge tank sizing - mine is about quart.

//RF

Re: Tbi swap build thread
 

Thanks for responding to my inquiry, RF. I don't use my truck off-road and/or operate it at extreme angles, so I don't have concerns about fuel sloshing in the old non-EFI tanks. I usually run each tank down to about an 1/8 full before switching over, but I have to admit to having gone below this level on occasion - I've had no starvation problems at any time with my generally sedate driving.

I mounted my Carter in-line pump on the inside of the frame rail slightly ahead of the transmission cross member. To minimize heat soak from the exhaust and possible vapor lock, I also fabricated an aluminum heat shield that I mounted to the frame rail. When I swapped out the lines trying to resolve the fuel pressure problem, as well as when I had to swap out the first pump that locked up, there were times the fuel in the supply lines gravity drained. Each time, the Carter primed fairly quickly afterward, which I attribute to mounting the pump at a level below the bottom of the tank.

Mark

Re: Tbi swap build thread
 

Ok guys I am having problems getting my set-up to run I have spark and fuel but it will not start with out dumpin gas into the tb I do have power to one side of each injector(should power be on both sides?) Is it possible my fuel pump puts out too much pressure and the tb is by passing it all?

Re: Tbi swap build thread
 

I do have power to one side of the injector while cranking but the other side does not flash?? (for some reason I cannot edit my posts)

Re: Tbi swap build thread
 

With ignition on, you should have 12V+ on both the red and white wires. The injectors do need a solid 12V, so if your battery is weak, they may not fire. The blue and green wires are triggered by the ECM to ground for firing each injector. There are ways to check the injector pulses at the wiring connectors, but require specialized equipment like an oscilloscope or trigger lights.

It is possible the injectors are stuck from having gummed up sitting around -this is what the problem was with mine when I first tried to start it and I was able to get one un-stuck by rapping the injector pod on the side with the handle of a large screwdriver. If you can get one to spray (the truck will run rough on just one injector), a good way to see if they are operational is to use a strobe from a timing gun. I ended up having to buy a new injector for one side.

I doubt that excessive fuel pressure is the problem - I'm pretty sure the bypass regulator is after the point where fuel is pressurized to the injectors. While I'm not sure what harm could be done since I've never tried this, you could try to momentarily connect a ground to the terminal of the injector that doesn't have 12V+ to see if it sprays (to try this, you have to have fuel pressure at the injector). If it sprays, there is either an ECM or wiring problem between teh ECM and the injector, otherwise it is probably the stuck injector I mentioned above.

BTW, I'm no expert on this, I've just been down this road before and I'm trying to give you the benefit of what little I know. Hope this helps and good luck.

Mark

Re: Tbi swap build thread
 

I lightly rapped on the injectors and nothing sooooo I guess I ll wait for a few others to chime in...

Re: Tbi swap build thread
 

While I get the sense that you want to figure this out quickly, these "noid" lights are the cheapest way (available on e-bay for $5-10) to see if all the wires at the injectors are getting the correct signal (i.e., determine if the lack of spray is due to the ECM/wiring or the injectors). Perhaps they are available at your local auto parts store.

BTW, I had to rap on my injectors pretty solidly before the one started spraying.

Good luck,

Mark

Re: Tbi swap build thread
 

Do you here your injectors clicking while you are cranking the motor? If you do they have the right voltage to fire them because that is the clicking noise. If they are clicking that probably means not enuff fuel is getting to the injectors.
I had this same problem and it ended up being a pinched fuel line.

I think the injectors get there signal from the ignition moduel in the distributor. If it is bad you might have spark but the injectors will not fire or vise versa.

keep us posted and good luck,
Jamie

Re: Tbi swap build thread
 

Perform the following check.

Turn ignition key into RUN position (do not crank). With a DVM measure voltage (with respect to engine ground) on both injector terminals - you should have voltage (11.5 to about 12Vdc) on both sides of the connector. Repeat for for both connectors.

If only one side has voltage you have injector with open winding (highly unusual) or injector connector that is not properly seated and engaged with injector pins.

Note the color of wires that have voltage.

When you pour a bit of gas into TB do you get engine firing up???

//RF

Re: Tbi swap build thread
 

Sorry, RF, but I respectfully disagree. Again, I'm no expert (I'm worse - I'm an engineer:lol:), but my understanding is that one side of each injector always has the 12V+ and the ground is switched/pulsed to the other terminal/side of the connectors by the ECM. Thus, testing for voltage across both injector connector terminals as you suggested will not show 12V (I just checked my truck and confirmed the lack of 12V across the injector connector terminals when in RUN).

With the key in RUN position, you should be able to measure 12V from the red wire on one connector (or the white wire on the other connector) to an engine or chassis ground, but not to the other connector terminal.

In regard to pouring gas into the TB, he said it would start in post #186.

cjracing: The relationship between the ignition module in the dizzy and the injectors is that the module tells the ECM that the engine is spinning (and at what RPM). The ECM needs to check that the engine is spinning because it is a potentially very dangerous situation if the ECM allows the injectors to fire (i.e.,release fuel into the TB) when the key is in the RUN or START positions and the engine isn't spinning. Since FB72 said his engine would start when he poured gas into the TB, the ignition module is working fine and it is my belief that his problem is (1) an ECM problem, (2) an open in the wiring between the ECM and the injector connector, or (3) a stuck/defective injector.

Since the injectors are basically solenoids, I reiterate my earlier suggestion to apply a ground to the non-12V+ terminal of the connector to see if the injector will fire. With a confirmed 12V+ on one injector terminal and a ground to the engine or chassis on the other, the solenoid/injector should click and allow fuel to flow. If fuel doesn't flow, either (1) the injector is stuck or defective or (2) there is no fuel pressure in the injector pod. If fuel does flow, then the problem is upstream of the injector connector in the ECM or wiring. While I've never tried this test, I don't see why it wouldn't work, nor do I think it risks harming anything.

That is my $0.02 and please understand that I am not trying to offend anyone or debate their advice - I'm simply trying to help.

Mark

Re: Tbi swap build thread
 

That's what I said. Kindly re-read my post (engine is not turning).

Furthermore, measuring voltage drop across 1.1 Ohm injector with a common DVM is fruitless. However, with a dual trace O-scope and A-B function one can measure voltage drop across operating injector. But that's not an issue here. In TBI system (same technique is used in many other injector systems as well) one pin of injector is tied +12 volt bus, while the second pin is being tied to a switching circuit inside ECM. Typically this switch circuit consists of high power Bipolar or FET transistor. In case of 1227747 ECM GM used a high power NPN transistor with collector tied to floating injector pin, while emitter is shunted to ground with 0.1 Ohm resistor. A custom (Delco) injector transistor driver IC is used to current limit current drawn by injector - by monitoring voltage drop across 0.1 Ohm shunt.

Missed that one, sorry.

OK = 2 cents accepted (in this economy)
//RF

Re: Tbi swap build thread
 

The batt in my voltage meter has decided not to play today so I quickly probed the wires and I have at least some power to one side of the injector connection on both sides injectors the other wire does not have any voltage(at least not that the test light shows) with the key in any position or while cranking the engine... Looks like i'm off to town for a battery for the meter.. Again guys thanks so much for the many good points of view..


Also on a side note I have a friend bringing over his scanner for the diagnostic port will this tell me anything ???

Re: Tbi swap build thread
 

I'll put together a basic measurement diagram later tonight - this should help you to troubleshoot. I hate guessing and once you have check list it will make it simpler to troubleshoot further.

Scanner
The ALDL will not tell you why injectors are not firing. On the other hand 7747 ECM will give you sensor data. Injector functionality is not monitored by early ECM - we are talking '80 high tech here (PC-AT, remember those 8086??)

//RF

Re: Tbi swap build thread
 

rfmaster - those diagrams you post up are great, and a bunch of help for someone who hasn't looked at a TBI since the early 90's! :lol: I take it you are making them?

Re: Tbi swap build thread
 

cjracing: The relationship between the ignition module in the dizzy and the injectors is that the module tells the ECM that the engine is spinning (and at what RPM). The ECM needs to check that the engine is spinning because it is a potentially very dangerous situation if the ECM allows the injectors to fire (i.e.,release fuel into the TB) when the key is in the RUN or START positions and the engine isn't spinning. Since FB72 said his engine would start when he poured gas into the TB, the ignition module is working fine and it is my belief that his problem is (1) an ECM problem, (2) an open in the wiring between the ECM and the injector connector, or (3) a stuck/defective injector.

Ok the way I understand how the cranking sequence works is the cpu gets a signal from the starter (C-9 prpl wire that goes to the selinoid on the starter)to turn on the fuel pump while it is cranking. When the engine has oil pressure the oilpress switch is what tells the cpu to run the pump and I understood that the module is what fired the injectors in time with the engine while it is running.
Am I wrong? If I am I would like the right sequence.

By the way FB-72 you have checked to see that you have 12 volts to the pump right? If you have and I missed it I am sorry I am just trying to help ya out.

Re: Tbi swap build thread
 

Cj if your talking about the fuel pump no I have not checked but the return line is filling up the 5 gallon can quickly... I have 12 volts dc to both injectors on one side only...

Re: Tbi swap build thread
 

Ok then your fp is ok then. How did you make it run so that it filled the gas can? Also when you crank the engine over do you here a clicking noise from the injectors?

Re: Tbi swap build thread
 

No clicking...... I did however find this wire unhooked any ideas on where it should go? It has power when the key is on??? Filled the gas can that im using for the return line while tring to start the truck....

Re: Tbi swap build thread
 

FrenchBlue72

Please Refer to figure below

http://67-72chevytrucks.com/gallery/...ctorWiring.jpg

Background Information
Basically, GM implemented a very simple TBI injector circuit. In this implementation ECM acts as a switch pulling Pin B of injector connector to ground completing the circuit energizing injector - fuel is delivered. Ignition switch supply is provided via two circuits 481, 482 (red and white wires) and are always on (as long as ignition key is in run or starting position).

Checks
Requires a functioning DVM - no excuses now, alright???
Injector coil
1) Everything is off, disconnect injector connectors from injectors by gently squeezing release tabs. Set DVM to measure resistance (Ohms), set to lowest range available <300 Ohms. Ignore this if you have a fancy auto ranging DVM. Measure resistance of each injector. Depending on your DVM and test lead resistance you should be able to measure individual coil resistance - about 1.1 to 1.5 Ohms for typical GM injector. If you are reading very high resistance - time to cry. If injectors check out then step 2.

2) Verify ignition voltage supply
With both connectors disconnected make sure that they do not come into contact with anything in the engine compartment. Once secured, turn ignition into run position and measure voltage at Pin A off each connector. With a good battery you should see 11.5 to 12.0Vdc with respect to ground (bat negative terminal). If there is no voltage verify ignition fuse.

3) Re-install injector connectors if step 2 is good.
With ignition on, engine stopped both Pin A & B should measure 11.5 to 12.0 with respect to ground. If Pin B fails to measure same voltage as Pin A then it is possible that connector is making a good contact with injector pins or there is an open injector winding when connector is installed on injector.

4) ECM PWM verification (this requires NOID or un-powered 12 volt test light)
For this test DVM a typical DVM response time is to slow (there are units that can measure frequency or pulses specifically for PWM circuit troubleshooting) and a simple un-powered 12 volt test light will do the trick.
Connect ground lead to engine ground and probe Pins A & B of each injector connector - light should be one for both as long as ignition is on, engine stopped. Get a helper to crank engine while probing Pin B of each connector - the light should be blinking off periodically. This is normal. Otherwise, if it remains solid that may indicate that ECM is not pulling injector circuit 467, 468 to ground. This may be caused by brake in harness, bad injector pull down circuit, etc. Manual shorting of injector control circuit - Pin B is not recommended, but this can only be done once supply voltage pind has been verified (red/white) and only for a short time.

//RF

Re: Tbi swap build thread
 

RF - thanks for the latest diagram. I now realize that the your statement about "both pins measuring 12V" that I originally disagreed with was because you were measuring the voltage with the connector attached to the injector. I normally disconnect things since it can be tough to get a probe on the terminals when connected - I assumed (the old ass out of you and me adage is correct in this instance) you were probing the connector when disconnected, which would show only 12V on the red or white wires of the terminals and an open circuit across the connector terminals like I stated. So, in retrospect, your statements are correct when measuring with everything connected and mine are also correct when disconnected. BTW - all your diagrams do ROCK!

cjracing: You are correct that that the ECM requires both a starter signal and oil pressure signal to fire the injectors, however, my understanding is that the oil pressure signal is not required when starting/cranking. That is, when cranking in START, the ECM sees the signal from the starter and doesn't look at the oil pressure as it realizes that the engine's oil pressure may not have built to a sufficient pressure as yet. Once started and in RUN, the ECM requires oil pressure to continue to fire. However, getting back to the start sequence, the ignition module signal to show the engine is spinning is also required by the ECM before firing the injectors. That is, if the ECM were to fire the injectors and the engine wasn't spinning, there would be a bunch of gas being introduced into the TB and manifold that could ignite out of the firing sequence - bad news. In summary, in START, the ECM requires the starter signal to tell it to ignore the oil pressure, but also requires an ignition module signal to tell it the engine is spinning before firing the injectors. In RUN, the ECM requires both the oil pressure and ignition module signals before firing the injectors. Hopefully this is now clear (as mud, I'm sure).

Mark

Re: Tbi swap build thread
 

Thanks - LOL yes, back probing injectors while they are connected is a bit tough but with skinny probes it can be done. Alternatively using small grabber style probe leads will do the same trick. Case closed - but we still have a problem with no start.

1227747 ECM uses starter motor (aka cranking) signal and DRP signal from dizzy to enable start up sequence, which includes enrichment sequence if CTS indicate cold coolant temperature. Now, the oil pressure signal is really a fuel pump voltage monitor. In these early EFI systems GM put a primitive back to keep fuel pump operating by installing (normally open - NO) oil pressure switch in parrallel with FP relay contacts. If FP relay fails, but as long as oil pressure is above 4-6 PSI the oil pressure switch will keep current flowing to the fuel pump.

FP relay (kinda) gets tested during POST sequence - ignition key off - on. SES light will go from on - off - steady on if all is well until engine starts. During POST ECM will try to power FP for about 2 seconds and shuts off. However, ECM monitors the FP relay switched side voltage when DRP are present and will set Code 54 if the voltage is low.

Official description------------>
Powertrain Controls - ECM/PCM
Code 54 Fuel Pump Circuit

CODE 54 - FUEL PUMP CIRCUIT (LOW VOLTAGE)

CIRCUIT DESCRIPTION :

The status of the fuel pump CKT 120 is monitored by the ECM at terminal "B2" and is used to compensate fuel delivery based on system voltage. This signal is also used to store a code if the fuel pump relay is defective or fuel pump voltage is lost while the engine is running. There should be about 12 volts on CKT 120 for at least 2 seconds after the ignition is turned, or any time reference pulses are being received by the ECM.

Code 54 will set if the voltage at terminal "B2" is less than 2 volts for 1.5 seconds since the last reference pulse was received. This code is designed to detect a faulty relay, causing extended crank time, and the code will help the diagnosis of an engine that "Cranks But Will Not Run."

If a fault is detected during start-up, the "SERVICE ENGINE SOON" light will stay "ON" until the ignition is cycled "OFF".


//RF

Re: Tbi swap build thread
 

FB72: that connector appears to be the EAC (electric air control) solenoid wire connector, which controls the air pump diverter valve. If you aren't running an air pump, no big deal - it can be left unconnected.

I say it "appears to be the EAC" since the connector in your picture looks exactly like the one on my '87 TBI harness (which has an operable air pump and diverter valve), however, your tan or yellow wire is not the same as my pink w/ black stripe wire - the color differences could be due to different model year harnesses. The yellow or tan wire (or pink/black in my case) should be the one with 12V+ with respect to ground when ignition is on (for clarity - I'm talking about probing the connector when removed). The brown wire is the same color as mine and you can confirm this is the EAC wire by checking continuity between the brown wire and terminal C2 on the smaller (24 pin, not 32 pin) of the two ECM connectors. Good luck.

Mark

Re: Tbi swap build thread
 

You know it is a good day when you learn something new... this statement struck me as odd, so I looked at the circuit diagram and you are correct. It looks like the only real purpose of the FP relay is to prime the fuel system at start up before oil pressure builds. This also explains my weird fuel pump "run-on" problem I mentioned back in post #177 - the oil pressure switch is connected to BATT 12V+ (as is a good portion of the rest of the FP relay circuit) and provides power to the fuel pump after I turn the ignition off until the pressure drops to the point where the oil pressure switch opens. Thanks for the education, RF... I just wish we could help find the problem for FB72.

Mark

Re: Tbi swap build thread
 

FB72: I made a mistake... terminal C2 is on the larger of the two ECM connectors (32 pin, not 24) - sorry.

Re: Tbi swap build thread
 

Well guys I just got off work im gonna roll the truck into the shop and lock myself in there..... Thinking cap....check....test light ...check....volt meter....check.... no kids check....yep good to go..