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Hot 355 runs awesome but won't idle..?

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dirtwarrior17

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I finally got this thing tuned up and timed today. Had a master mechanic that is a friend of my dads come and see if he could figure it out. We timed it and got it running like the beast that it is. You stab the throttle and its at 4000 before you can let off. the motor runs great and fires up and can just tell its gonna make big numbers but i have to give it throttle to start it and keep it running. He says its just real rich when it starts up cold and i have to get it running for more than 2 min to let the temp gauge register. I have yet to get it out of my driveway because of cali registration/smog laws so the temp sensor has probably not even moved. Is it just the temp sensor or do i need to get my psi to the tbi down... i have about 35 psi goin to it right now because im attempting to make 375-400 hp with a tbi 355.
 
You making enough vacuum to keep the MAP sensor happy? Barring a vacuum leak of course, which is always evidenced by a problem with starting/idle.

I haven't messed with the MAP setups yet, but I know vacuum at idle is critical to good idle.

I'd head over to thirdgen.org and peek at the TBI forum, and see what others have come up with if you are positive you have no vacuum leaks.

winALDL is going to be your friend if you haven't done squat with the PROM and trying to run a monster motor.
 
Do you know where to get winaldl? The computer is stock... pretty sure you know what i have on the motor. I have been told that the prom will affect how it runs but it should still idle.

I guess im gonna try and burn my own chip. Do i HAVE to have a labtop?
 
Stoopalini's post

There's a link to winaldl there.

Like I said, no experience with MAP myself, but I guarantee idle quality is governed by the ECM.

IAC tries to keep the engine idling, if the MAP reading changes wildly from a large cam, it can't compensate fast enough, but TRIES.
 
DW17,

I am having the same problem. I am currently running a 670 Holley TBI and a Holley Projection manifold.

When cold, the TBI runs too rich, so rich, black smoke pours out the exhaust. I have replaced the emission coolant temperature sensor because the old one didn't test correctly, but it didn't help. The engine will run fine after 2-3 minutes.

In order for the engine to run normal when cold, I need to disconnect the coolant sensor, then it runs fine, then I can connect it when the engine is warmed up.

I have given up trying to determine what the problem is so I wired a switch to the sensor, that allows me to disconnect the switch from inside until the engine is warm, then flip the switch. I know, kinda stone age but it works.

I am now wondering if it's inherent with the Holley 670. BTW the engine is a stock 350.
 
Sounds like it is having issues until the computer gets a reading from the o2 sensor... Maybe installing a heated o2 sensor will help solve the problem since it will send a signal to the ECM much faster than a regular one?
 
Sierra,

You know I never even heard of a heated o2 sensor until a few days ago on this forum. I didn't make the connection until now, do you think that may be my problem as well?

Where do I find one of those?
 
I think in my case its the o2 sensor and the fuel map becasue i have headers and a lot of psi going to the tbi. I will Try to disconect the temp gauge and see if she idles tomorrow still too loud. I got to wait awhile until i can run this thing all the time because my neighbors are pissed from 2 weeks of open headers.

Did it run alright when it was cold... when you gave it gas or it just didn't run?
 
throw a vaccum gauge on that manifold somewhere. Just to test it. That camshaft might be just a bit too large and messing with the MAP sensor. I told you, if TBI has any kind of lope, its gonna be messed up. My 89 burb with 355, only has 1 wire O2 sensor and the temp sensor takes a while to register but it idles pretty darn well. The only issue is when you impose a load while its cold it spits and sputters a little.
 
dirtwarrior17 said:
Is it just the temp sensor or do i need to get my psi to the tbi down... i have about 35 psi goin to it right now because im attempting to make 375-400 hp with a tbi 355.
Click to expand...

Stock TBI runs at 10-14 psi tops. The intank pump only puts out 14ish. I think you have waayy too much pressure going to the TBI. The temp sensor is irrelevant until the motor is up to temp and running in closed loop anyway as I recall.

John
 
Yes, sounds like the O2 sensor input is really helping control the motor.

Too much change in the engine for open loop operation it sounds like.

Changing to a heated O2 sensor will likely help, because it will speed the closed loop process up, but it won't solve the inherent open loop issue that exists now. Can't be good for the engine to be running that rich really....lots of carbon developing on the plugs, chambers, etc.

I suspect that with the temp switch you have rigged up, the engine thinks the temp is extremely high, cutting the amount of fuel it's getting by a large margin. Only major diff for this particular issue between cold/hot temp for the ECM is amount of fuel dumped for cranking.
 
Yes, really bad to run in such a rich condition, especially on a brand new engine. It only ran twice that way and only for short periods of time.

Once the engine is warmed up and the sensor is switched on it runs fine. I used the winaldl program and it's pretty close, the ecm could be tweaked a tiny bit, but close enough. BTW DW17, winaldl is a super product.

I do have headers and the only reason I put the Holley intake on because the stock manifold was junk, the water jacket sealing surfaces were totally corroded away.

I am thinking about going back to stock or using an Edlebrock TBI intake with the smaller TBI bores, so I can use the stock injectors.

For $90, I am not sure if I want to try the heated o2, unless it's 100% the solution.
 
got to to agree. I will have about $400 in 2 weeks to thro at my truck and It sounds like i will have to get a chip burned in order to get this thing to idle... Cam specs are at .050 .272 dur, .447 lift with a bone stock PROM. I don't understand how it doesn't idle but then runs pretty damn close to perfect as soon as you bring up the rpms? too much lope at idle for the map? Already turned up the idle.

The motor has only been run for about 15 mins tops in this condition but is brand new never even been on the road. Carbon buildup is not an issue right now but will be if i don't fix this. I need to run block seal through it for 20 minutes at idle to seal up the water leaking into my oil(bad intake seal) IF i open the throttle it seems to run just fine at about 900 rpm. Can i run the block seal for 20 min or wait until i get a chip?
 
why not fix the prob? pretty stupid to run a block seal type product thru a brand new motor imho... i hope you haven't been leaving milky oil in that thing...
 
The only problem is the manifold water jackets didn't get rtv. Block seal will do the same as the rtv. without taking off the coil, dist., temp sensor, cps,vaccum lines, belt bracket, and exposing the combustion chambers.

As for the water.... it's bad but not corrosion bad. It's been tan(not milky) I really didn't have a choice but to leave the water in there for a little over a week becasue i already tried torquing the manifold with a torque wrench then did an oil change and still had water in the oil. I have run it for about a min everyday of the week so i am sure no corrosion has taken place YET. I am maxxed way out on money and literally can't afford another 6 quarts of 10w-40. I have 6 qts of cheap crap but i need to make sure i get the water out before i put the new oil in but..... the block seal needs to be run through the motor for 20 mins and my foot throttle is not hooked up because holley wants me to buy a 50 dollar adapter. I need my brother to hold the throttle while i top off the tranny fluid then put the block seal in then change the oil and oil filter. Hopefully it will all be done tonight.
 
DW17

At the risk of repeating what some one else has written, because I haven't read the thread completely; I will say this. You computer is still programed for the stock cam and TBI. This engine demands MORE than the computer is programed to give. Sounds like it's time for you to learn how to burn your own chips, or at the least, talk to Brian at TBIchips.com. He can get you in the ballpark, but YOU will have to finish it off.


SS396

You are having the same problems that I had when I mounted my 670. You WILL have to make some changeds to the chip too. Here's why. You chip still thinks that you have the stock TBI with the stock injectors on it. The Holley uses Delphi injectors that flows MUCH more than the stock GM units do (and NO they will NOT interchange...BTDT:mad: ). Because of that, the injectors pump out WAY more fuel than the stock injectors with each pulse. Now, here's what needs to be done: shorten the base pulse width, lean the ENTIRE fuel curve out, lean the cold-start mode out, and add a bit of timing to take advantage of the Holley.

I had Brian (www.tbichips.com) burn me a chip that got me really close (that same bin *should* get you really close), and learned to do the final tweaks myself thru a third party who burned the changed I made into the chip. I have a few more that I want to make, but I'll wait until I get my Prominator.

If y'all don't already have it, download yerself a copy of WinALDL (it's a freebe) and do some datalogging to see what is really going on. Also head over to www.thirdgen.org and take a peak at the DIY PORM board. A word of warning though, DON'T ask for somebody to give you a bin or burn you a chip. These guys are VERY admanit about burning YOUR OWN chips. Now with that out of the way, do some searches and reading over there. They have a wealth of information and there are some real experets who hang out over there.
 
DW, I think you really need to remove the intake and reseal, I think you are going to do serious damage to that engine. If you have anti-freeze in your oil, chances are you are going to wipe out the bearings.

It really wouldn't take that long to R&R that manifold, I know it's a PITA but you would be better off IMHO.

Good luck.
 
Ok Heres what im goin to do....


Pull all that **** off tonight and seal the water jackets up with blue rtv then when i get that done i will have to get a chip burnt as soon as possible... one problem tho I can't afford to buy a laptop or the software to burn my own chip and just got this truck a year ago (17 years old) and had my license suspended for possesion of marijuana so i have only been on the road with this thing for about 6 months and don't have the resources to burn my own chip. I did but the guy moved 3 months ago. I really want to put it on a chassis dyno and get it down to the tenth on my air/fuel because this thing wants less fuel down low but im gonna guess its gonna want a lot up top. I can't drive it that far unless I get some $$$ from my dad to get some temp registration and i still don't know how this thing is gonna pass smog but i got to figure somethin out.

appreciate the help.... im off
 
Whats happening with your motor is due to the fact that you upgraded quite a few parts on the motor without upgrading your prom. You added a cam and new tbi. Just the cam alone would need a prom re-program. When you added the new tbi, you have over pushed your limits with the stock chip.

The reason its running crappy when cold is because the stock chip cant keep up. The new tbi will deliver a lot more fuel. When the engine is cold, it cannot read info from the oxygen sensor (the computer cant read the o2 sensor until it warms up to about 150-160 degrees), so it uses a set cold specification. With the stock prom, it still thinks that your motor is getting the 11-13 psi that the factory used when in actuality it is probably getting more like 14-15ish. When the oxygen sensor warms up enough to allow the computer to read it, it adjusts to your running conditions. This smooths the motor out. I dont even think 35 psi like you stated it was getting is even possible. If your pump is stock, then it will stall around 15-16. If it is aftermarket, 35 psi would be far to much for your engine to run. Where did you get this pressure reading?

Anyways, to alleviate this problem you can do two things. You can either burn a new chip or buy an adjustable pressure regulator and guage, and turn the fuel pressure down. If you buy a chip, it will solve your problem while giving you maybe 10-20 extra hp. If you buy a pressure regulator and turn the pressure down, it will run better when cold, but you will compromise some of the power when hot. The pressure regulator and guage will run you about half of what the chip will.

As far as the block seal is concerned, why would you use a $3 bottle of cheapo block seal on a brand new engine? There are times when you can do things cheap (if the motor had 200k on it) and there are times you have to do it right. Take the few hours its gonna take you to take the intake off and do it right with some orange or grey rtv. A couple hours to do that will be a lot less than putting in a new engine when you smoke a bearing due to having water in your oil. If your getting $400 in a few weeks, buy a new chip, fix the intake, and buy some nice oil. That should solve your problem.
-Harrison
 
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