Hello all. Great Forum! First post but have been lurking for a while.

I have a '68 Land Cruiser with a SBC 350. A while back I converted it to TBI with a junkyard donor. The improvement in performance has been wonderful. However, I have a lingering problem: cold starts.

It fires up beautifully and for the first 3 seconds runs like a dream. Then it starts to sputter and tries to die. It seems to be running way too lean. As the engine warms the problem fades until it reaches normal operating temp at which time it runs great.

I have tried a number of fixes but believe it is related to my 02 sensor. I run WINALDL and the voltage reading hovers at .451 to .459 (if I recall correctly) and never moves outside this range. Is this a normal reading? I thought the O2 numbers should bounce around a lot more. BTW, this a three wire heated sensor.

Thanks in advance for your help!

-Ed

 

sounds more like a lack of fuel upon startup

 

On start you are in open loop. runs off VE tables and the OL RPM/A.F/MAP tables. .45 is neither lean nor rich but considering you are "cold start" cool coolant temps it should be .75-.90 or rich. Once coolant temps are 150-160F it goes closed loop and then the switching of NB02 sensor occurrs(over .45) as seen in your datalogs. then you get BLM feedback to alert you to need to change VE tables accordingly.

What is your fuel pressure? If you dont have a gauge consider borrowing one at autoZone.

 

Thanks for the input so far guys.

I do have a fuel pressure guage and an adjustable regulator. I have it running about 12.5 psi. I replaced the coolant temp sensor just in case, even though it seemed to be working fine. I have also replaced the O2 sensor but I still get the same voltage readings. I have verified it is getting 12v power and tried grounding to different locations to see if that would help but no change.

Would my unchanging O2 sensor input cause the ECM to not richen the fuel mix while the engine warms up? Or am I barking up the wrong tree?


Thanks again!

-Ed

 

Make sure the egr isn't opening at idle, or that its stuck open alittle.

 

That is a sign you are not in CL. When I am OL I see a static 02mv. Typically I see .7to .85 as my VE fat(yet). I am OL at idle and closed throttle and under 15 MPH.

Check the settings for CL to be allowed to occur. I am and always was nonEGR so you may want to do search on faulty EGR and its affect on CL-OL and BLM.

 

Tried the EGR. No change. It does not seem to be stuck.

Forgive me as I'm not very savvy with winaldl or PROM editing, but I should be in open loop on start up, right? When I start it, after the first three seconds, the idle speed drops and it runs too lean to stay running w/out me giving it gas. Shouldn't it the RPM's flare on cold start and drop steadily with increase in operating temp? The ECM is not getting the message that the engine is cold. Since my coolant temp sensor seems to be functioning properly where else would the ECM normally get this information? That's what led me to look at the O2 sensor and its seemingly strange behavior.

Thanks for the advice so far guys. Any additional thoughts and advice are welcome!

-Ed

 

Yes on cold start the engine(mineanyway) idles about 1000 and hangs there till about 140F and then drops to commanded 850(manual trans). My engine only flares up when warm. You need to witness the IAC functioning. Key on it will cycle full closed to full open. When started it should remain open and then when engine warm>160F will be nearly closed (95%).

I agree. Have you installed a FP gauge? Maybe you need to increase FP? If no gauge I would add and see what FP you are getting 11-13 is what I would suggest is adequate to run OK.

I understand when a coolant temp sensor fails it adds too much fuel. But you replaced the CTS.