Re: Tbi swap build thread
 

Oy. So, best to keep fairly close, year to year? Seems a bit of a mess. I'm fine iwth swapping the housings, but the rest is a tad muddy. Thanks for the info, though, answered a lot of questions.

Re: Tbi swap build thread
 

I have a question regarding the EGR solenoid.My CEL comes on spuratically.
I have checked vacuum at TBI=0 at idle,increases with throttle.
no vacuum at egr side of solenoid with engine on or running with throttle.
I can move the egr valve manually and the idle changes,but doesnt stumble.
Does this sound like i have a BAD solenoid?
Vehicle in question is 1989 Suburban R2500 454 TBI(2wd),automatic.
Thanks!

Re: Tbi swap build thread
 

Follow up questions:

1) CEL comes on sporadically - which DTC codes are set? Get wire jumper across pins A & B of ALDL and count CEL flashes (groups of 3 starting with 12)

2) If you apply vacuum to EGR valve with a vacuum pump you should see the valve move and there should be some change in idle quality. Too much EGR and the engine should stall. On high millage trucks there is a lot carbon and oily crud build up in the EGR passages restricting amount of exhaust gases reaching intake manifold plenum. The best thing to do is to carefully remove EGR valve and take a small brush and carb cleaner and try to remove, clear the offending crud.

Depending on EGR type you have it may hold vacuum or slowly bleed it of. A blown diaphragm will leak instantly - use a hand held vacuum pump to check EGR diaphragm.

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).

If you do not see vacuum then I would check ECM control circuit. The EGR solenoid connector should have two wires - pink-black and gray. The pink-blk should have +13.8 Vdc when engine is running (IGN is on). The gray wire is a control circuit - ECM will pulse this line on-off to control amount of EGR. Most DVM's averaging is too slow, but higher end DVM's may have a frequency function and can pick up the PWM waveform. Naturally Oscilloscope is the a weapon of choice!

//RF

Re: Tbi swap build thread
 

At the moment I cant remember the codes,but I do remember it saying the EGR system,check for operation of the valve,check the solenoid,check the plug to the solenoid.
The CEL light comes on at very strange times. I have driven half way to Sacramento(200 miles) with it NOT coming on,then I have driven down the street about 5 miles and it comes on.
I do plan on cleaning out the EGR passage,so a new valve may be in order anyway.

Re: Tbi swap build thread
 

Well, lets get some basic information squared away before jumping to any conclusions. Pull codes - they should stay put in ECM memory unless battery was disconnected. We'll go from there on.

//RF

Re: Tbi swap build thread
 

Code 32 comes up. I checked the pink/black wire at the solenoid,on my DVM it reads 12.01. I dont have a vacuum pump (other than my wife!lol),so I have to draw vacuum the old fashioned way. When I do there is NO movement n the egr valve when the vacuum source(me) is hooked to the manifold side of the solenoid with the key "ON" engine "OFF".

Re: Tbi swap build thread
 

I hooked a vac gauge up to the egr port(between solenoid) and drove it in town and freeway. Vac reading never got above 5" and would stay there for about 10-15sec and then drop to 0.

Re: Tbi swap build thread
 

EGR solenoid acts as a proportioning device - metering amount of vacuum that reaches EGR valve diaphragm. The fact that you see about 5" inch of vacuum between EGR control solenoid and EGR indicates that control circuit is functioning, but EGR valve diaphragm bleeds off vacuum very quickly. Not being a betting man I would say that you may have a leaky EGR diaphragm. You can temporarily connect EGR valve directly to a manifold vacuum port and if there is no movement - it is time to replace EGR valve!

In the absence of the handheld vacuum pump I would take it off and take it to a parts store - most of the time they have handheld pump handy.

//RF

Re: Tbi swap build thread
 

Thank you very much.

Re: Tbi swap build thread
 

An - unrelated question! On your '89 454 Burban you do not have an AIR pump, right? Is it CA or Federal certified (do you know). The reason why I am asking there was a post recently with a question when GM stopped using AIR on BBC TBI trucks.

//RF

Re: Tbi swap build thread
 

It's a CA truck w/A.I.R.

Re: Tbi swap build thread
 

Another question, would a leaky diaphragm also be the reason it will hold 5" for 10-15sec. and then drop off to 0,repeating that over and over. Or is that the way the system operates,open then close cycles?

Re: Tbi swap build thread
 

I basically have a 1991 suburban with a 208 transfer case with speedo cable.

I need VSS instead of the mech. speedo cable

From reading and research it sounds like I have 3 options:

signal generator - plugs into transfer case speedo cable (do I need Electronic Ratio Adapter??)
reluctor ring/speed sensor - plugs into tail housing of tranny
reluctor ring/speed sensor - plug into rear diff.

Can someone explain which would be the best option? I'm still confused here.

Thanks for any helps guys/gals

Re: Tbi swap build thread
 

What about the optical VSS speedometer used in the 87-89 square bodies with TBI? Mechanical speedo with an optical sensor on the back that feeds the ECM data after passing through the DRAC.

Re: Tbi swap build thread
 

???

Re: Tbi swap build thread
 

VSS produces AC wave signal - ECM expects a square pulse (digital like signal). DRAC module is a signal conditioner - multiplier, divider if you will. Another alternative to DRAC is a Dakota digital 'swiss army' knife ratio adapter. Pricey, but very flexible. I would expect a mechanical speedometer cable to turn 1000 times per mile travel - this is how conventional mechanical spedometers operate. But these hybrid early 90's systems are something else - need to refer to FSM to find out. Do not know.... Sorry.

//RF

I hope this helps

Re: Tbi swap build thread
 

This was in reference to fuel pressure regulator???? Or ??

Re: Tbi swap build thread
 

Would this be the easiest/best option? I really didn't consider this because I just finished building/restoring the gauge cluster out of the suburban.

thanks

Re: Tbi swap build thread
 

Sorry, I was meaning the EGR valve diaphram. The vac would rise to almost 10" and then fall to zero then back up to almost 10" and fall again...constantly. I keep getting the EGR system CEL code.
I have not driven my 'burb very much lately since I got my '82 diesel. But none the less I would like to get it fixed. Thanks

Re: Tbi swap build thread
 

This is normal operation of the EGR system. However, I suspect that you may have defective EGR control valve - it is being constantly being pulsed by ECM. Over time the vacuum switch (inside EGR control valve) may have developed an intermittent and just stays in a vent position until it gets its 'marbles' again. The duty cycle and frequency of the EGR control voltage pulse determines how much EGR valve opens and allows exhaust to enter into intake manifold plenum.

//RF

Re: Tbi swap build thread
 

THANK YOU! I will get a new one,but I also plan to remove the EGR valve and make sure the passages are clean/clear.
Thanks again rfmaster! You're the man!

Re: Tbi swap build thread
 

I believe it is. All the gauges other than the speedo from your 91 cluster will fit right into an earlier housing so the work you did is not wasted.

The optical VSS mechanical speedo clusters are pretty cheap and easy to come by too plus the wiring will be just like shown on the stock wiring diagrams for the earlier cable speedo TBI trucks, Suburbans & Blazers. No point reinventing the wheel here when stock parts will do the trick.

Re: Tbi swap build thread
 

not just TBI trucks,trucks with cruse control used a 3 wire buffer that outputs the correct signal,the 3 wire is gm#25007227

Re: Tbi swap build thread
 

Wow, this is a long thread! Lots of great information. I installed a 1991 TBI engine in my '56 Chevy last fall and was successful getting everything hooked up correctly. I'm having one issue though. The car stumbles slightly on acceleration. Tonight I performed some tests on the throttle position sensor. Gray wire is reading 5v, ground wire is good, but the blue wire isn't reading correctly. At idle, I'm not getting any voltage on the meter. I have to move the throttle quite a ways before I get volt reading on the meter and then it jumps up to about +1.6 volts. At full throttle I'm getting about 3.5 volts. From what I've read, I should see about 0.4 to 0.9 at idle and about 4.5 volts at full throttle. I bought a new TPS and got the same results. Any ideas why it's acting this way?

Re: Tbi swap build thread
 

Can you rotate / adjust the orientation of the TPS so it starts reading voltage at idle? Mine have slotted mounting holes to allow you to do this. If not you could slot the holes on yours to give it this capability.