Re: Tbi swap build thread
 

I should have read the posts before mine. I see you recommend the following test for EGR solenoid function...

"Depending on calibration EGR valve is enabled when truck is in motion and certain other parameters are met. To check for EGR vacuum control side operation I use a vacuum hose and T with a vacuum gauge temporarily mounted on the windshield (duct tape can be used). The vacuum take of point is between solenoid and EGR valve. If you see vacuum while driving - solenoid is supplying vacuum to EGR valve. Check EGR diaphragm first. Check supply vacuum hose as well (between TB and solenoid input)."

I'll give this a try next.

Re: Tbi swap build thread
 

Ok, just test drove the car with a vacuum gauge hooked up to the EGR valve vacuum line. Solenoid appears to be working. Gauge showed 0" in/hg while coasting (foot off the accelerator) and parked at idle. Between 15-20 when cruising (maintaining speed with accelerator slightly pressed). Under harder acceleration, the gauge was down near 10. Does this sound right?

Re: Tbi swap build thread
 

Yes, it is about correct. So it looks like control side of the EGR system is working as designed. The question where the slight stumble is coming from.

Can post your engine configuration (if known) such as compression, cam, over bore, CID, heads (casting numbers, reworked, etc) etc???

From the notebook....
A a slight stumble of idle usually due to to little fuel delivered by injectors. This is usually due to a low fuel pressure - common in high mileage cars or trucks. A new fuel pump usually solves this problem. I usually go further and rework TB, clean injectors, etc. Stock TBI system calls for 9 to 13 PSI operating fuel pressure. That's a very large range, percentage wise, which can affect acceleration enrichment (AE) significantly. A drop of 1 PSI of fuel pressure under light acceleration indicates weak fuel pump or clogged fuel filter.

//RF

Re: Tbi swap build thread
 

The engine is a bone stock 305 from a 1991 Firebird. It was a fairly low mileage engine when I got it (87k). It was a budget rebuild so I just freshened it up with new gaskets, bearings, and rings. The ECM is #1228746 and currently has a PROM for an automatic trans, but the '56 has a 4-speed. I just bought another #1228746 ECM with the AXKU PROM for a manual trans. Do you think I'll notice a significant change in drive-ability?

Thank you for your help thus far. I'll see how it runs with the new ECM and go from there.

Jason

Re: Tbi swap build thread
 

That's a good question. I do not have BIN file for '91 Automatic F-Body, but I was able to locate stock AXKU and compare it against ANTS ('89 F Body automatic). The main spark advance table has some differences.

Notable differences:

Knock retard values
EGR on/off threshold values
Close loop CTS threshold
Over speed threshold
DFCO RPM threshold
AE wall wetting vs. differential MAP
AE pump shot vs. differential TPS
VE table #1
PE thresholds and AFR mixures
BPW - injector constant multiplier vs. IAT

In other words there are numerous small differences. I am assuming that you have a functioning VSS - if not that may explain a stumble.


//RF

Re: Tbi swap build thread
 

Yes, I have the JTR #2PRS VSS installed, however I occasionally get a code 24 which I don't understand. I'll report back when I get the AXKU installed.

Re: Tbi swap build thread
 

One more question for you guys (sorry this is all new stuff to me)

I again basically have a 1991 suburban but have a 208 TC behind the 700R4. I bought a JTR #2PRS so the computer is now happy. I thought this would fix the speedo as well but it doesn't (was assuming this VSS adapter had a reluctor in it).

Why wouldn't this new signal that is being sent to the computer reach the speedo as well?

Thanks for the help guys/gals.

Re: Tbi swap build thread
 

The 1990-1991 truck should have the Digital Ratio Adapter Controller (DRAC) module found behind glove box. DRAC converts the input AC signal from the VSS to a calibrated digital DC signal. The DRAC sends 2,000 digital pulses per mile to the ECM (Electronic Control Module), 4,000 digital pulses per mile to the cruise control module, and 128,000 digital pulses per mile to the ABS (Anti-Lock Brake) computer. DRAC is configured from the factory to match vehicle's stock gear ratio, and tire size, but, it can be changed by moving jumpers around.


For more in depth info see this thread:

http://coloradok5.com/forums/showthread.php?t=124012

//RF

Re: Tbi swap build thread
 

Update: I got the new ECM installed with the manual trans PROM. Not a drastic difference overall, but helped with what I referred to as a stumble. Before when I'd accelerate from a stop, I had to work the clutch (more than what should be required) so it wouldn't stall. Now, it seems much easier. Also, the idle speed seemed higher with the other ECM. So, I'm happy with the overall improvement in drive-ability.

I know this doesn't quite fit on a truck forum, but here are some pictures of my project car. It's a 1956 Chevy 210 Series 4-door station wagon:

http://dl.dropbox.com/u/12200294/195...%20Wagon_1.jpg

Before with the original 265 V8:

http://dl.dropbox.com/u/12200294/195...%20Wagon_4.jpg

After, with a 1991 305 TBI:

http://dl.dropbox.com/u/12200294/IMG_3364.jpg

Re: Tbi swap build thread
 

Very nice - 56 station wagon still qualifies as a truck (well sort of)! The 12 SI alternator upgrade is a definite improvement - since it can supply 92 AMPs of current to power most common electrical circuit (there were lower rated units as well).

Do you have BCC code from 5 speed ECM????

//RF

Re: Tbi swap build thread
 

BCC code is AXKU

Re: Tbi swap build thread
 

what are the improvements with the TBI system

Re: Tbi swap build thread
 

That's a loaded question!

In a summary - stock TBI system was designed to support 180 HP LO5 (350 CID) motor. With a combination of EPROM reprogramming, larger injectors, higher fuel pressure, better camshaft, heads, exhaust a 300+ HP level can be achieved. Naturally 700R4 needs to be beefed up if truck is equipped if this type of trany.

//RF

Re: Tbi swap build thread
 

thanks
www.chacalanay.com

Re: Tbi swap build thread
 

OK...I am going to bring this to the top as I now have a problem...Today I was jump starting a truck...1987 GMC 3500 with a 6.2. I was using my 1989 Chevy Suburban R2500 w/454 TBI,TH400 2wd to jump the '87. My suburban ran GREAT all day. while hooking up the jumper cables, I got a pretty good spark from the '87's side of the jumper cable(negative side of the jumper cables) My 'burb started having problems staying running. it would run for about 30-45 seconds and die. But start right back up. Did this repeatedly....and still does it.
I had it towed home(about 70 miles). I still have power to the 'Burb,but it just stops like the key was turned off....Did I pop the computer when I saw the "spark" while jumping it? What should I look for? Thank You AGAIN.

Re: Tbi swap build thread
 

Tough to say.
1) There are several EFI related fuses - they may have been stressed, but not blown. Enough current was pulled to heat up the fuse metal but not long enough to fully melt it. As you start pulling current fuse opens after 30 seconds. IRC there should be BAT fuse, IGN and injector fuses - just simply R&R.

2) Check fuse links at the firewall BAT terminal - where alternator +BAT wire is connected - make sure non of the fuse links are melted and all bolts are tight. Loose bolt or corroded lug will cause weird things to happen.

3) If it stop like the key is turned off I would check +B to ignition coil with a DVM. In other words put DVM to read DC volts and connect and secure leads to read voltage right at the coil plug (pink wire). If voltage drops out when engine stops you found it. The other voltage test is injector circuit power (red wire). If both check out then ECM swap would be my next step.

//RF

Re: Tbi swap build thread
 

Check or replace your HEI ignition module. A bad one will act just as you describe.


Shawn
Posted via Mobile Device

Re: Tbi swap build thread
 

Thanks guys!

Re: Tbi swap build thread
 

ok, I am back with my results....no loss of power to the coil(pink wire) and no loss of power to the injectors(red wire...actually all the wires for the injectors have power)....I don't have a burnt fusible link....ECM?

Re: Tbi swap build thread
 

My money is still on the ignition module.
Posted via Mobile Device

Re: Tbi swap build thread
 

Module tested fine. So I picked up a reman ECM. I replaced it 2 yrs ago this month...wife reminded me it was doing the very same thing. SO I will replace it in the morning.

Re: Tbi swap build thread
 

Re: Tbi swap build thread
 

Based on this posting - our wife's know everything and they remember everything! ;)

Darn - sorry to hear that it end up being ECM! They were designed to handle surges, but if enough sparks fly one is asking for it..

//RF

Re: Tbi swap build thread
 

Hello all. :new: My TBI swap build is about to commence in about 2 weeks, one basic question i have while i am gathering parts is, can i use the harness out of a 89 c20 van with the 1227747 ecm? Will the harness out of the van be the correct length to reach all of the sensors since it will be going into a squarebody c10? The one in this van is the only one i can find in the local boneyard that is intact and untampered with. Will this harness require extensive modification in order to work in my squarebody?:help: This is an awesome thread BTW!!!

Re: Tbi swap build thread
 

Welcome to the thread Max

In the past I have looked at using VAN harness for conversion. I have looked at Astro van and later 94-95 full size vans as a possible source of harness's as they tend to be the last to be looked at by JY marauders. The van harness and 1227747 ECM from the same van should work, but expect to spend time going over each circuit as they tend to run longer than usual C/K harnesses. The 89 C20 van EFI harness should be more a less stand alone harness with few extra circuits tied into the main bundle. The later, post 1990 harnesses were fully integrated with the rest of the engine bay circuits and require extensive 'skinning' (just like a deer) to extract EFI only circuits. It generally takes couple of hours, plenty patience to clean and extract needed EFI circuits. See photo's posted earlier in the thread. Make sure that donor has the same engine type (V8) and CID as the transplant recipient. If it is a direct swap - it should be a straight forward operation. There are couple of gutcha's but there are easy to traverse.

//RF

Re: Tbi swap build thread
 

Thanks for the reply! im hoping to find a c/k harness but they are all torn apart, connectors missing/ broken. Thank you for the input, im sure i will have more questions once the build begins.

Re: Tbi swap build thread
 

okay, I ended up finding a 87 c10 to pull the haness out of and a 1227747 ecm. Im going thru the harness now and I found a vacuum sensor that ive never seen before. it was mounted on the intake manifold on the passenger side. It is not the standard MAP sensor for these trucks, it has 3 vacuum ports and a 2 prong electrical connector. But the harness also has the standard 3 prong plug for the standard MAP sensor. Im confused as to if i need this weird vac. sensor. Wish I had a pic but i cant find anything like it on the web and am unable to take a picture at the moment. Any help would be greatly appreciated!

Re: Tbi swap build thread
 

Sounds like it may be the EGR solenoid or something for the AIR system. Post a pic.

Re: Tbi swap build thread
 

It is probably mounted on the back side of this bracket (you can see light gray and pink/blk wire sticking from connector - upper right) MAP and ESC modules are visible.

http://i226.photobucket.com/albums/d...Picture025.jpg

and looks something like this:
http://67-72chevytrucks.com/vboard/a...1&d=1250628500

It is called EGR solenoid.

//RF

Re: Tbi swap build thread
 

I found out what the switch was, it was the EGR solenoid. the MAP and ESC was missing so i will have to track one down. One question i have is, how do i merge the new TBI harness with the original harness? i pulled the entire harness from the donor truck, fuse box and all. What wires will i have to tap into to merge the two harnesses? Thank you

Re: Tbi swap build thread
 

Well if you have the entire truck harness, check it over real well and replace your entire harness.

Re: Tbi swap build thread
 

What year is your square body??

The 89 donor harness will require some work. Generally, I leave original engine bay harness intact. The EFI harness will require two separate IGN-on connections (in run and crank) - both should be fused, one direct battery connection - fused, park neutral switch, VSS input, fuel pump supply, starter cranking circuit, SES light and ALDL connector (I hope you grubbed that). The donor harness is reworked to remove unneeded circuits, but that depends on several factors - AC, TH350 or 700R4, etc. It would be a good idea if you post what you have and what you are planning to install. Also list ECM broadcast code (BCC) - four letter ID code on the tag. All of these connections have been previously described and schematics are posted in this thread.

//RF

Re: Tbi swap build thread
 

my truck is a 85 c10 305. and 700r4.the ecm i have is a 1227747, BCC is ARJT out of a 91 burban. i got the entire harness out of a 87 c10 and would like to retain cruise and AC idle compensation. i have the fuse block and bulk head connector but i dont know what will be necessary. will i just use fusible links to fuse the few circuits that need power? I would like to make the TBI harness completely standalone if possible and leave the truck harness original. I am all about original and factory options operable. Thank You all!

Re: Tbi swap build thread
 

To start

Lay down 89 harness flat on the garage floor and take a photo

//RF

Re: Tbi swap build thread
 

Ok i am about to pull my hair out, I have been going at this for a year and cant get my truck running. I have traced down every wire and down continuity tests umpteen dozen times. I am getting 12v everywhere i should, grounds are good, I have a couple diferent ecu's.

I found a flow chart on chevy thunder and used it. One thing it told me to do is to unplug the harness that goes to the distributor and give one of the wires 12v. I did and the fuel pump turned on and the injectors started to pulse. That tells me that the wireing and ecu are good but the ignition module are not.

With a new dizzy, cap, and coil I still have no spark.

Thoughts???

Re: Tbi swap build thread
 

Make sure that dizzy (pink wire) gets +12 volts during cranking - very common oversight. Also, make sure that injector supply circuit (two red wires) is ON (eg +12 volts is present) when ignition key is in cranking and run position!!!!

//RF

Re: Tbi swap build thread
 

The pink wire that goes to the coil, is that what you mean because yes it has 12v.

Re: Tbi swap build thread
 

and yes the injector supply has 12v also.

Re: Tbi swap build thread
 

Is there any way to test the distributor

Re: Tbi swap build thread
 

I am going to assume that you have an external coil, small hat HEI.

An HEI distributor, as a complete unit, together with ignition coil - must provide spark during cranking (under 400 RPM) and send DRP signal to ECM. Individual components in the HEI distributor can be tested => ICM can be tested at better auto parts stores, HEI coil can be checked with DVM, reluctor coil (inside distributor) can be checked with DVM. Another often overlooked item is a two wire harness between dizzy and coil, as well as electrical grounds. All of these may contribute to no start (no spark condition).

//RF