Re: Tbi swap build thread
 

I thought about that, but it wouldn't help. If I test the sensor off the TBI and rotate it with a screw driver, it doesn't make much difference. The WOT reading is a little higher, but I still have to rotate it a little to get any voltage reading at all.

Re: Tbi swap build thread
 

That's odd to say the least. You should be getting voltage on Pin B (TPS signal) at all times (while ignition is on). The best explanation I can offer is that TPS sensor has a defect. It is not uncommon for a high mileage TPS to wear-out a certain potion of the potentiometer - aka TPS.

From your description you have a newer style TPS unit - with a slot (AC-Delco 213-895) vs. vertical level arm (AC-Delco 213-3859). Both types, electrically, should provide continuous voltage output at idle (between 0.3 to 0.9 Vdc) without any change in the throttle position. I would start by replacing TPS with another one.

//RF

Re: Tbi swap build thread
 

I already tried a new TPS and got similar results. I need to check the specs on my multimeter and see what the range is. May not read that low.

Re: Tbi swap build thread
 

Hmmm, if your DVM has a 20 volt range it should be able to read idle voltage. Alternatively, disconnect harness connector from TPS, switch DVM to read resistance and measure resistance between A & B and B & C. I always screw up these values that you should see (going from memory), but at idle A & B (black & blue) should read about 1.3 to 2.0 kOhm and B & C (blue to gray) should read between 6.5 and 7 kOhm and between A & C should be around 6.15 kOhm (verified) with TPS mounted on the TB (throttle shaft is engaged into TPS wiper arm slot.

Getting further into this problem I pulled one of these later model TPS sensor from my storage bin and sure enough if there no tension applied by the throttle shaft on the TPS rotor slot the DVM reads infinite resistance! So I can safely confirm that what you are seeing is no fluke. What needs to happen is that some rotational displacement must be provided by the throttle shaft to move TPS wiper arm coupler from its absolute minimum travel position. Playing with screwdriver and DVM, here at bench, it appears to be a very tiny amount of TPS wiper arm rotation. The two TPS mounting holes provide some slop - I would try turn TPS body about shaft centerline until correct TPS values are observed.

//RF

Re: Tbi swap build thread
 

OK, false alarm. It was the meter. With another meter with a lower range, I'm reading .54v at idle and 4.5 volts at WOT. The voltage increases smoothly as I move the throttle. So, the TPS is working as it should.

On to my next question, which is regarding the EGR valve. I don't think it is functioning. I performed the following tests, which I found on another forum. My results are in red.

Shut the engine off and connect the tester directly to the EGR valve. Pull vacuum (around 15 inches is plenty) and be sure it holds for a minimum of 20 seconds. If it does not build or hold vacuum, the valve could be held open by a chunk of carbon, which you could attempt to clean out – but most likely, the valve is bad and needs to be replaced. With vacuum applied, valve held open for well over 20 seconds.

If the valve passes the hold test - with vacuum still showing as holding on the tester, have a helper start the engine while you watch the gauge. The vacuum should bleed off immediately. Vacuum bled off when engine started.

Determine whether the EGR passages in the intake are clogged by carefully depressing the EGR diaphragm with your fingers. Take care to not burn your fingers or get them caught in the openings under the EGR. When you press the diaphragm, the engine should stumble noticeably, and possibly stall. If there is little or no response, the passages in the intake are likely clogged with carbon. Effective cleaning of these passages requires removal of the intake manifold. This is a recently rebuilt engine, so I know the passages are clear. When manually actuated, the engine did stall.

Check the vacuum source to the EGR solenoid. Connect a vacuum tester (Mityvac) to the line leading from the TBI unit to the front (single port) side of the solenoid. There should be full vacuum at idle, around 20 inches/Hg on a stock engine. If not, remove the line from the TBI and connect the tester directly to the TBI to verify vacuum. If none, the port itself may be clogged. Vacuum read 22 in/hg at idle.

Reconnect the line from the TBI to the solenoid and move the tester to the line exiting the rear of the solenoid. At idle there should be NO vacuum reading (be sure you purged your gauge if necessary so that it reads zero before connecting.) Snapping the throttle should show some activity on the gauge as the solenoid briefly commands the EGR open. DID NOT pass this test. Vacuum gauge needle did not move at all.

With the meter set on ohms, you can test the EGR solenoid coil across the two pins in the socket; any reading less than 20 ohms indicates a bad solenoid winding. Reading was 43 ohms.

With the meter set on DC voltage, or using a test light, check the EGR solenoid harness terminal A (pink/black) to ground. Key on, meter should read 12V or the test light should light up. Do not pierce the wire to test, simply unplug it and touch the test lead to the connector pin. Meter read 12.36v.

So, from these results, it appears that the EGR valve itself is not the problem. However, the solenoid may or not be working correctly or it may not be receiving a signal from the ECM. Any thoughts on this one? Do you know of any other tests I could perform on the solenoid before I go buy a new one?

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
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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.
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