Need some help with my 4.3 CPI

ain'tstuckjustresting · Apr 12, 2011

Installed this motor in my Yota and just haven't been able to get it running right. Engine was newly rebuilt when I got it. It's a 4.3 Vortec CPI out of a 94 S-10 Blazer.

Pretty much everything is new. I kinda started with new stuff since it's a new engine.

NEW: CPI, Nut kit, fuel lines, filter, fuel pump, cap, rotor, plugs, wires, coil, MAP, IAC, IAT, PCV, Howell harness & Prom.

TPS and ECT are not new but tested good.

Fuel pressure steady at 60Psi

Timing set at 0deg

The problem is it runs really rich and won't idle. It surges up and down about 5 times then dies. If you hold the rpms up it'll stay running but runs very rich. Seems to do it warm or cold.

Here's the thing, if I pull the vac line off the booster and use hose pinchers to have a regulated vac leak it runs really well. If i pinch off the hose about 90% the idle comes down to 800rpms steady and smooths out. It will sit like that for an hr running great exh smells pretty clean. After about ten min of running I checked the field service mode and it was in closed loop w/ no CEL. A few min later the CEL came on (Code 35 IAC fault).

With the vacuum line hooked up it runs like ****, almost like the IAC is closed too far and it's not getting any air.

I read that after IAC replacement you need to drive 40mph for the PCM to command the IAC to fully closed and reset itself. Well ****! I don't have the VSS or DRAC hooked up because I'm running a TH350. How the hell do I get the IAC to reset? OR, is this even my problem?

Thanks Guys............................

GaryTJ · Apr 13, 2011

This is going to be a fun one. You need to see what the computer is seeing to be able to do any good. Without a scanner, I would try 2 things. Check all the powers and grounds to the computer first and do a voltage drop test on them, NOT an ohms test. Second would be to try and see into the intake (hard I know) to see if there are any leaks at the connections for the fuel lines inside the intake.

beyond that you need a scanner to see actual info.

Binder · Apr 13, 2011

ain'tstuckjustresting said:
Here's the thing, if I pull the vac line off the booster and use hose pinchers to have a regulated vac leak it runs really well. If i pinch off the hose about 90% the idle comes down to 800rpms steady and smooths out. .....

The IAC resets itself every time you turn the engine off. No need to drive it anywhere.
You may have the wrong IAC. Put the old IAC back in and try it.

JOOP · Apr 13, 2011

If the TPS is not calibrated/adjusted correctly it will surge. It's looking for an idle RPM.

I'm trying to remember how to do this. But unplug the IAC, adjust the TPS for 0.54 volts? With the key on. Then start the vehicle and plug in the IAC.

I think thats how you do it. You can look online and see if thats the correct procedure but it's something like that.

Binder · Apr 13, 2011

JOOP said:
If the TPS is not calibrated/adjusted correctly it will surge. It's looking for an idle RPM.

I'm trying to remember how to do this. But unplug the IAC, adjust the TPS for 0.54 volts? With the key on. Then start the vehicle and plug in the IAC.

I think thats how you do it. You can look online and see if thats the correct procedure but it's something like that.

You have to drive the IAC closed before unplugging it. If possible adjust both the IAC and TPS at the same time.

Here is all the adjustment information. This site is specific to TBI but should work fine for what you're doing.:awesomework:

JOOP · Apr 13, 2011

Binder said:
You have to drive the IAC closed before unplugging it. If possible adjust both the IAC and TPS at the same time.

Here is all the adjustment information. This site is specific to TBI but should work fine for what you're doing.:awesomework:

I was close, just trying to remember off the top of my head. :awesomework:

Hip · Apr 13, 2011

I gots the scan tool for this.

i just went through this and figured it out on my own with these guys input, but im pretty knowledgable about this system now.

who did the harness?

start there pin by pin. make sure thats right.

if you can get it to my shop im sure i could help ya get to the problem.

ohh i had just bought a new harness and prom also

IAC and TPS are not adjustable.

ain'tstuckjustresting · Apr 13, 2011

I bought the harness and eprom from Howell EFI. I got a copy of the pinouts and haven't found any discrepancies yet. Not serious supply voltage issues like you had either. My TPS is dead nutz .6v at throttle closed as per spec, so I don't see why that would need to be adjusted to .54 as listed in the link from Binder.

They guy at Howell was a douche when I called him, pretty much no help. He said they test all the harnesses and chips before they leave so there must be a problem with the engine or ecu

.

I'm pretty sure all the TBI info in the link is for the older ecu with the black plugs mine has the red and blue plugs. I'm not sure that info will work on a Vortec.

I just had the plenum off last night to double check everything. It was oily in there from the very rich exh being pumped in by the egr but there was no fuel pooling around the lines or regulator. I cycled the pump a few times to make sure there were no leaks.

I made a block of plate for the egr just to eliminate a stuck pintle. I'll remove it once I get it running decent.

I'm pretty much at a loss here.

ain'tstuckjustresting · Apr 13, 2011

Hip, did you have to use the DRAC or VSS? When I bought the harness they said none of that was needed for the engine to run, but when I talked to the douche at howell Friday he said he thought the DRAC needed to be hooked up.

ain'tstuckjustresting · Apr 13, 2011

Piss, I just walked outside and open the hood, now it's blowing about 30mph and hailing...................................:booo:

Binder · Apr 13, 2011

ain'tstuckjustresting said:
I'm pretty sure all the TBI info in the link is for the older ecu with the black plugs mine has the red and blue plugs. I'm not sure that info will work on a Vortec.

Yes that's correct. Don't use that page for pinout or pin voltage info......
From what you described it sounds like your IAC may not be working properly which could be defective or the system could be giving it the wrong signal. You said you replaced the IAC. If you installed a IAC meant for a big block the wires are swapped around in the connector. Common problem. Try your old IAC.....

Binder · Apr 13, 2011

Hip said:
IAC and TPS are not adjustable.

Both are adjustble but they weren't intended to be adjustable from the factory.:;

ain'tstuckjustresting · Apr 13, 2011

The IAC was one of the only things I hadn't changed but I pulled it out Monday to clean the port and was f-ing with it and the pintle shot out:eeek: So I figured I better go get a new one. The problem was occurring before replacement. This IAC is specific to the CPI motors. The passage is way different than on a tbi. You can't actually see the end of the pintle through the intake.

ain'tstuckjustresting · Apr 13, 2011

Well the procedure to set the IAC didn't work, when I started it with the IAC unplugged the pintle must have been retracted because it idled @ 3000rpms and I could feel massive air flow into the IAC passage.

Binder · Apr 13, 2011

ain'tstuckjustresting said:
Well the procedure to set the IAC didn't work, when I started it with the IAC unplugged the pintle must have been retracted because it idled @ 3000rpms and I could feel massive air flow into the IAC passage.

You mean you tried to drive it closed but this didn't work? Good chance it isn't working right.

You didn't just unplug it and try to start the engine did you? When the engine is off the IAC is part way open.....

JOOP · Apr 13, 2011

Hip said:
IAC and TPS are not adjustable.

My TPS is adjustable. (GM TBI system) The IAC just calibrates to the TPS.

Binder · Apr 13, 2011

Is this a screw in or bolt on IAC? If it's bolt on I don't know if the big block vs small block thing still applies...

zukkev · Apr 13, 2011

Thing about the IAC is....whether it's full open, or full closed, isn't gonna cause a rich run condition like you describe...all it does is allow more or less airflow bypassing the throttle plate to adjust idle speed....---the rest of the sensors used in the system will (or should) calibrate your air/fuel ratio based on the IAC's position....something else is goin' on here.:;

Binder · Apr 13, 2011

Also make sure you have a full charge on the battery.....Low voltage can make it do strange things....

ain'tstuckjustresting · Apr 13, 2011

I did the procedure as stated, jumping the aldl, key on, unplug IAC, key off, remove jumper, start engine.

This is a bolt in IAC. The pattern is just a hair different that the TBI manifold I have in the shed so I don't think you can screw it up.

So this is what I tried: I created a metered vacuum leak (Booster line and clamp) and closed it down to achive the lowest smooth idle w/o surging (about 900rpms). I put my finger over the IAC port and can't feel any vaccum so the pintle must have closed. I open the throttle a bit and can feel the IAC start to pull vacuum on my finger. It must be reacting to the TPS command and allowing more air in to increase rpm. If I continue to block the IAC port with my finger and open the throttle more it will pull even harder through the IAC port. In a correctly operating system this is what you would expect right?

So now I guess I need to figure out why the hell so much fuel is being commanded at idle. I don't think the IAC can add enough air to keep it running w/o the idle reving up. As soon as the idle increases the IAC trys to get back to base rpms and the engine floods. :scratchhead: