I would appreciate some others experience on a gen 2 350 tbi conversion. I have just completed it and it is so lean it flags o2 lean and kicks out of closed loop. For those who have performed a similar conversion (stock motors), how far off was the stock 350 chip? I just want to know whether I should look into burning a new chip or not. I would have thought the 2 motors would have been close. I just dont want to waste a bunch of time and money on a new chip and find out it was not the problem at all. I am frustrated. I would appreciate some help.

 

When you say Gen II I assume you are talking about an LT1. If that is true then you HAVE to get into chip burning.

LT1's are the source for the lt1 cam of course and those cams in a stock motor need tuning. So throw in some better flowing heads and you have a tune that isn't even close to what the engine needs.

You mentioned a lean flag, are you logging? If so what do your BLM's look like?

How about a complete description of your whole combo?

 

BMmonteSS

I do not think that he has LT1. From earlier post it looks like 88 truck motor.
https://www.thirdgen.org/forums/tbi/...onversion.html

ECM 7747 with ASDU.

Again, a complete description is needed to debug.

One more idea, even though you may be seeing 13 psi of fuel pressure, do you have enough volume????

How big are your fuel lines (3/8" would be OK)???
How big is return line???
Which FP are you using (in-tank, in line)??
Do you have AIR injection exhaust manifolds?
What type of exhaust system do you have (headers or stock)??
Which O2 sensor do you have (model number 1, 3, 4 wire)?
Where is O2 is located (how far is it from engine)??
Do you have 65 LB injectors (Orange-Black)??

 

Excuse my ignorance of chevrolets. I am much more versed in ford blocks. It is a gen 1 motor with open chamber heads normal compression and early 1980s stack cam from camaro I believe. I acquired teh jeep in a swap and the motor was already there. I did not build it so thatis the reason I am a little vague. The fuel volume should be fine. 3/8 lines both sides. It was a MPFI jeep and I am using the the intank pump. The specs on it show it should be more than plenty. the exhaust is shorty headers with o2 bung just below collectors. o2 sensor is bosch 13077 3 wire heated. they are 55 LB injectors. The intake is a stock tbi manifold from 88 truck. When I initially started engine afeter install the timing was at 8 btdc and I had a regular o2 sensor. It would actually go into closed loop then and the blms were in the 150s and o2 was .1v. I thought maybe problem was lack of heated o2 sensor. So I changed the sensor and reset timing andnow blms will read 130s but it will not stayt in closed loop. I have removed plugs and made sure it was actually lean, real lean. Lean enough to miss and run like crap.

I realize I am not as advanced as many of you are. I am sorry to bother but the help is appreciated.

 

Just to verify, when you checked the timing was it with the EST wire disconected? If not then most likely your timing is way retarded. You should see around 20 degrees with the est wire hooked up.

A severly retarded engine will put lots of unburnt fuel and air into the exhaust which will show up as a lean condition.

We're never bothered to help, just need all the info to make an educated guess as to what the problems is. Do you have a log of the engine kicking in and out of closed loop? We might be able to spot something you would miss.

 

beardb

There are a lot of guys on TGO that can help you figure this problem out. Transplants and retrofits can be challenging at times.

Since you have a heated NBO we can assume that O2 is at operating temperature. To make sure can you verify that O2 sensor is drawing current - with AMP meter.

Timing is definitely worth checking - BMonteSS is right. Your engine with timing connector open should be around 0 to 2 degrees - good enough for just about any stock to mildly built SBC.

I would also check ground path resistance between O2 sensor bung and O2 sensor ground - Pin D6, Tan wire, Circuit# 413. I do not trust headers to provide low resistance path back to ECM sensor ground. Ground loops are always tough to figure out, hence I run four wire O2 sensor 15732 which has a dedicated ground return wire.

Can you data log (WinALDL or TP)??

 

the timing was set with wire disconnected. It is sitting around 20 now reconnected and fluctuates as should during rpm change. THe ecm will only go into closed loop once. It will start and run for a minute or so and then kick into closed loop. the blm will start climbing up and then after about 30 seconds or a minute it will flag o2 lean and never try again, unless keyed off. The web posts I got the heated o2 info form said to put one white to hot and one to ground and of course the black wire to ecm. THe o2 seems to be working correctly. Before when the regular o2 sensor was in it would never bump above liek .01, but now it fluctuates like it is supposed to and reads usually around .25. I dont really understand why it kicks out of closed loop now with the o2 working correctly but before when it read severely lean, it would go into closed loop and the blms would go all the way to 150's. I will check the ground path. i am out of town now, but will check this weekend. I am using winaldl and can log data. Will it log blms in open loop? THanks again for the info.
----------
do you guys think it would be plausible that the chip is that far off?

 

The O2 malfunction code is causing it to drop out of closed loop. The ECM thinks the O2 sensor is bad. Codes 13, 44 & 45 will do this.


If they are truely 55 #/hr injectors that will be an issue. Can either raise the fuel pressure or use a larger injector (61 to 68 #/hr are stock on 350's).

RBob.

 

Why would th 55 LB injectors be such a problem for a stock 350? They were used on the truck 350's. I guess they just dont have any room for any extra? Would it be better to increase the fuel pressure or just increase the constant in the chip? I am certainly a novice at the chip stuff, so excuse errors. I guess the increase in FP is easy and free, except for gasket. Does any one know a NAPA or Oreilly P/N for the gasket needed when regulator changed?

 

The 55 #/hr injectors were only used on 305's. The 350's received the 61 through 68 #/hr injectors.

Do you have the numbers and/or color codes of the installed injectors?

RBob.

 

I got the following info from diy-efi web site tables. is it not correct? I have the 5206 orange black injectors. I will confirm again once home, but I already checked this once when I first started lean.
Color codeApplicationFlow ratePart #Black/White1-3/8" bore 2bbl, from 2.8l truck???GM 5235430 *RPDYellow/Blue4.3L???GM 5235203 *RPDGreen/White5.0L40 lb/hrGM 5235279 *RPDOrange/Black5.7L pickup55 lb/hr GM 5235206 *RPDYellow/Brown5.7L Cop Car65 lb/hr???Blue/BlackLate big block pickup80 lb/hrGM 1708430 *RPDDark Red/Dark Bluebig block pickup90 lb/hrGM 5235231 *RPD

 

The TBI injector flow info on the diy-efi.org board is incorrect.

The ORG/BLK '5206s are 61#/hr at 13 psi. If it is as lean as you say, then either the fuel pressure is dropping off, or the tune is way off.

RBob.

 

fuel pressure is 11 all the time. Not dropping off. What would you start with, new tune or just bump fuel pressure. WOuld it make since for the truck broadcast chip to be that far off. My engine is stock, just earlier heads. If it is the tune would it be likely that bumping the fuel pressure would be enough to get it close enough for the computer to fix in closed loop, or would it still need a new chip. In that case couldn't I fix both problems in the new chip by increasing the base constant, or is it already maxed with those injectors.
Brook

 

Try fuel pressure first - change spring in the regulator or go to AFPR. I am running 14 PSI which appears to be ok for my disco era 350. 11 PSI is on a low end of acceptable pressure range.

//RF

 

How are you checking your pressure under load? Fuel demands will be the least at idle, even bliping the throttle will not recreate the fuel loads you'll get going down the highway.

With that said, ccracin has quite a lean condition on the bottom end with his setup as well. We aren't completely sure why but the BLM's level out by 2400 rpm and he's as much as 20% lean down low. The more TBI vehicles I mess with the more I realize that even the smallest differences can require huge changes in VE to make right.

If you plan to ever modify the engine any more than it would pay to get into chip burning. You just can't beat having complete control over the engine.

 

rfmaster,
which injectors are you running? I am going to try upping the pressure this weekend. I saw the instructions for the afpr in the archives I believe. Is that a reliable modification? can I just by the gasket, I am sure mine will fall apart, or do you have to buy a whole tbi kit? thanks for all the suggestions.

 

I'm running a LO-3 setup on my L-98. with a LO-3 prom and it does fine

 

Beardb

I am using 61 LB '5206 injectors. I had them cleaned and flow tested before putting my TBI system together. I have to go and dig up flow test data but they were within 5% of each other and around 62 lb at around 13 psi and much more at 47 psi.

I am using JET AFPR 61500 - see pictures of my TBI setup during mock-up stage.

Some people prefer V-AFPR which was used on BBC engines. It is advantageous when used with 90 lb injectors on SBC TBI, but requires VE mapping, tuning and consequently PROM burning. For all its worth once you bump that pressure up a bit that lean flag will most likely be nothing but history. BTW, TBI injector flow rates are not linear with pressure. So a little bump may have a huge effect.

//RF

 

what about the article where you make the stock one adjustable?

 

Yea, I recall that DIY VFPR article:

http://350.streetracing.org/tbi.htm

I took the easy way out by buying kit.

 

Well you guys were right. I dont know how i was even getting 11 psi. THe spring in fpr was in 5 pieces. I replaced it and bumped fp tab 1/8 inch. It runs much better, no more lean flag. It will run in closed loop. It still has a hesitation when accelerating. The blms at idle read around 143, but as soon as you bump throttle they go back down to 128 even 123. The o2 is reading rich at idle around .7 or .8v. A short log is attached. I will log more later. Do you think it is too much fp causing the hesitation now?

 

Your BLM's are saying lean (above 128) and if you are in closed loop (O2 sensor in use) your O2 voltage will be swinging wildly as this is how the ECM works. The O2 can switch back and forth over .450 volts several several times between each snapshot of data. So in other words if the closed loop flag is checked don't bother looking at the O2 voltage, just look at your BLM's.


You might try adding some more fuel pressure and see what you can get your BLM"s down to at idle. Then go for a road test and see where you are at. What you are doing is globaly moving your fuel curve up and down. You can only hope that the shape of the curve fits what your engine needs. You may find that x pressure gets you perfect 128's at idle and pig rich 108's at part throttle. Then the only way to correct the situation is to jump into chip tuning.