rsanders

I have a '95 TBI truck... 7427 ECM, 0Dh mask. I just installed a Comp XE 250 cam (.432"/.453", 206/214 @.050, 111 centerline, 32 degrees overlap) and the performer TBI intake. I was (probably incorrectly) thinking that the stock binary would be good enough to fire the engine and start work. Long story short, I have spent two weeks of looking at the mechanical and trying changes to the code the engine to idle. I have read almost everything in the sticky list and I have read tons by doing searches, but I can't seem to get the first step done in getting this thing to run. When I quit tonight, I had it almost idling. The main issue I see is that the vacuum is pathetic. The cam should be showing 19" at 850 RPM, but I am measuring 3-5".

The cam timing, base ignition timing, valve adjustment are all correct. There are no obvious vacuum leaks (intake has been resealed once already). New IAC, temp sensor, O2, MAT, PCV, hoses. The MAT voltage in datalog corresponds to a mechanical vacuum guage.

I have uploaded the TunerproRT datalog of the engine idling and the modified rom I am working with. Anyone that feels like throwing me a life vest please jump in. I am almost at the point of reinstalling the old cam/intake just so I can drive something besides my motorcycle to work.

http://www.moates.net/files/6)%20Mis...rely_idles.zip

Z69

Did you degree the cam?
You wouldn't be the first person to get the wrong
cam with the p/n you ordered stamped on the end.

Check your egr.
If the valve is hung open if will idle like doodoo.

I don't recall if that intake has a warmup passage.
But if it got cross connected to the plenum. You'll get lots of egr. This isn't really possible on a lot of manifolds though.
But I did it once on an intake that was.

Check your plug wires for firing order.

Feel exh for dead cylinders if possible.

You have to have a big vac leak to drag it down that far.
Or some other big mistake.

You might want to change the subject header.
It sounds like a different question currently.

Grumpy

If you have something mechanically wrong none of this will help, but, it may help to get it at least idling.

Take and jumper A->B in the ALDL connector like you're trying to get codes. But, just turn the key on, and after a minute unplug the IAC. Then key off. Doing this will close off the IAC, and remove one variable. Then open the min idle setting like 1/2 a turn. You might have to play with the pedal, and min air but after a few attempts it should at least idle.

Quadruple check that you have stabbed the distributor right.

The second you get it turning try to get the base timing set.

Oh, and fouled plugs or almost fouled can make it a losing situation.

Might also look to see that the injectors are spraying during crank, and first run.

HTH

rsanders

I did not degree the cam except to use a dial indicator to make sure it was installed correctly after I could not get it started (ended up pulling the timing cover and checking the marks anyway).

EGR was blocked as part of the debug, firing order has been checked (and checked and checked). It runs for long enough that I got the base timing to 0 (pulled the set timing wire). I have also dropped the cat to check for restrictions.

The injectors are firing... actually pouring until I pulled almost all the fuel out of the idle table. I am getting crosses at the current settings, but I am not sure if that's just the NB lying or what. If I pull more fuel out it will not run at all. 57 in the VE table seems way too high just to make it idle.


I will zero the IAC and change the plugs after I get this posted. I have pulled the plugs and cleaned them before... they were pretty bad shape from the injectors dumping fuel on them. I hit them with degreaser and sandpapered the electrodes... but hey, 8 bucks after however many hundred is not going to kill me.

One thing I forgot to mention last night is that once it does get started, if I bring the RPMs above about 1800 the vacuum comes up (15" @ 1800-2000) and it cleans up pretty well. Runs like I would expect it to with the airflow changed that much anyway. I can see the signal drop when revving and rebound when closing the throttle quickly. It's only around-idle RPM that's the problem.

Doesn't the fact that the vacuum comes up that high at a still relatively low RPM pretty much rule out a vacuum leak? At least one of the magnitude required to cause almost no vacuum at idle? I have sprayed carb cleaner around all the gaskets, plugged the EGR/CCP/PCV/booster, and cracked open the valve covers listening for the leak but I have nothing.

I'll borrow a degree wheel tonight/tomorrow and check out the cam if the plugs don't work.


Thanks for the ideas guys! This is the first intelligent input I have had.

Grumpy

The ecm has some *stall saver* pieces of code in it. So if the ecm things the engine is going to die, it will try to prevent that, once you raise the RPM up, you get past that, and the engine can be somewhat normal.

With EFI, you need to have EVERYTHING close to right, less then that and you have to go item by item to get them there.

BTW, if anything you used in the engine assembly had silicone in it, you may have killed the O2 sensor, and that adds another layer of headache. Setting the Closed Loop Temp Enable to some ridicuously high enable temp would help with that.

Brent

iTrader: (1)

My bet is on a mechanical issue.

I looked at a '95 Suburban that had a cam with 212/212 duration @ .050 & 110 LSA installed in it. Without any tuning it idled and drove. Not very nicely, quite rich, but it was not disabled. Seems to me your cam should atleast run similar.

Not wanting to be insulting but are you sure the rockers aren't adjusted too tight?

Brent

HaulnA$$

O.K., this is right up my alley. I am VERY familiar with the $0D mask and TBI trucks. I looked at your .bin and log. First, I will start by saying that your stock chip should be fine to get you going, your cam is nowhere near big enough to give you the problems you are having. You have a mechanical problem and assuming that you have the cam and distributor are right, it seems vacuum related. From your description you either have a serious vacuum leak or the MAP sensor is conected to a ported vacuum source. It should be connected to the back of the TBI. Secondly, your .bin. I see that you are using the BDWM BCC which is for a '94 350 2wd 4L60e truck yet you show that you are running a '95 4wd 5spd truck. What is the BCC in your original Memcal? You should start with your factory .bin and tune from there. As I mentioned, your stock .bin should be good to start with. The timing and fuel tables in your posted .bin are all jacked up. Start over. Lastly, your datalog. Grumpy mentioned stall saver yet I never see the stall saver bit go true in your log. Your idle MAP stays around 85 kpa, not good. To me this says vacuum leak, possibly around your EGR block off. Assuming your O2 sensor is working properly, the O2 volts seem to support this as the idle PW is near 2mS (should be around 1mS) yet the O2 volts show way lean but this could also be a damaged O2. IAC counts aren't bad, they start out normal and drift high in conjunction with low O2 volts. IMHO you should pull the plugs and check 'em, re-verify all mechanical items and start over. HTH

rsanders

Changing plugs and zero/unplug the IAC helped a ton. Now it 'idles' at .59 TPS, 1400 RPM, 2.6ish MAT. Now at least it acts like a vacuum leak, even if I can't find one anywhere.


Trust me guys, nothing is insulting at this point. The rockers were adjusted to 1 turn past zero lash as per GM manuals. During all this I readjusted them to 1/2 turn past zero lash on a suggestion from a Comp Cams rep.

The MAT sensor is attached to the back of the TBI unit. The MAT voltage readings match mechanical readings taken from the EGR port, so I know the no-vacuum is real. I blocked the EGR during the debug... it acts the same with a real sensor attached.


The stock bin will barely start the engine. I have to floor the accelerator to get it into flood-clear to get a start, but the low vacuum reading is causing the ECM to dump fuel in. Emough that I have raw fuel and soot blowing out the exhaust. I realize that the tables in my current bin are all screwed, but I was starting from these instructions:

http://www.diy-efi.org/gmecm/papers/tunetip.html

The bin as it stands will start a hot engine immediately and it will run almost good. Well enough that I can run experiments that require the engine started.

As for the code, the truck started as a 4L60e with the BJYK BCC. I downloaded the BDWM code, because that was the only HAC available, and modified the tables to match the BJYK when I assembled it. Then I set the AFR Mode Word 5 (or Digital I/O Mode word depending on who you want to listen to) at offset 400Fh, bits 6&7 to disable the transmission control. That was my 'base line' bin... it got to the mess it is in now out of desperation.


I am starting to lean toward a casting flaw in the intake. If you guys don't think that additional experiments with the code are in order, then I am going to reinstall the stock intake tonight. It acts like a vacuum leak, but none of the normal check procedures is finding anything.

tail

I had a very similar problem with my first build. I had multiple problems, but I will tell you what they were in hopes you can rule them out.

My car wouldn't start and we kept messing with the timing. I would verify it was set to 6'btdc, but it wouldn't run. If we advanced it to about 12' to 15' it would start ok, but would adventually start having problems. I was constantly messing with my timing and VE tables, but as it turns out, the block I used (roller block) had a flat tapt cam. My cam retrainer from my 305 wouldn't fit the block. Like an idiot, I left it off. My cam was walking back and forth and I ate up two timing gears on my distributor.

I also know that it idled like crap, ran ok around 1200-2000, but towards 3000, it would bog and die. Try adding some timing at the distributor, see if it will at least start and run.

Other than that, I have to agree with them, sounds like a vacuum leak, maybe a bad valve, or possibly a faultly intake.