I just completed a significant restoration on my 89 C-4 engine 5.7L. It wasn't a complete rebuild. In hind sight maybe should have been, but only 50k original miles and garage kept until now.

I had the heads machined and trued locally due to a head gasket breach at cylinder 7. it caused an over temp and water pump leak issue, so I bought into everything. So, here's the list: rebuilt heads, piston tops cleaned, new stock head gaskets, new high output water pump, new headman LT ceramic headers, lower intake tanked and ported, plenum cleaned and ported, new plugs, accell wires, new cap and rotor, throttle body disassembled and cleaned, new idle air cont valve, new 02 sensor, TPS adjusted to .54v, and all new gaskets and seals for the above. I also recently installed all new injectors.

The problem is: I can idle at about 700 rpm, but when I add pedal it stalls. I can't seem to get above 1700 rpm (by nursing the throttle) . It doesn't smell of fuel, and no fuel leaks anywhere.

The exhaust is open at the header collectors, (no cats or pipes or anything after the collector flange reducers)

Is it possible that the open exhaust is preventing me from getting rpm to increase?

Thanks in advance.

 

Is the O2 Sensor installed and connected? Is the timing set correctly?

 

Check the timing. Are the valves set correctly?

 

Thanks:
Yes, O2 sensor is in the collector on the drivers side and hooked up. I ajusted valves for zero lash at TDC and then added 3/4 turn more for each.

 

Also, I don't have any fault codes displayed.

 

What is the fuel pressure at idle and when attempting high rev ?

 

As stated recheck the timing. How's the fuel pressure? Do you have access to a scantool?

 

I agree with Agent 86 here...there are good posts out there on what it should be.

We rebuilt my son's '88 this summer and did a lot of the same work; however fuel rail pressure ended up not being the issue.

One more thing that could be causing your problem if pressures at idle and rev are ok...i'm not sure if you are a TPI intake system but the Throttle Body position sensor could be sticking. We had a similar problem but not to your extreme and this was definitely the culprit.

You can pick up one of these reasonably from rock auto or other on-line vendors....

 

Thanks everyone for the help. Timing is at 6 deg BTDC. The throttle position sensor moves fine and produces varying voltage throughout it's range. I need to check fuel pressure again. I checked it prior to the rebuild and it was fine, but I suppose sitting for a few months may have caused an issue.

 

Paul Rugerri,
What kind of scantool are you referring to? I guess the answer is no since it's not OBD2. I may be able to get my hands on one though if you think it will help. Are you thinking laptop software type?

 

Oh, I guess that you all believe that I should still be able to develop HP even without the back pressure from the missing exhaust? In other words, missing exhaust after the headers should NOT make a difference on my ability to rev.

 

Having it un-caped shouldnt cause any problems.I had this problem before and it was a ploblem with the mass airflow sensor.Good luck and keep us posted.

 

Thanks everyone. I should be able to check fuel pressure, mass airflow connection, throttle pos sensor again, O2 sensor connection again, tonight. I'll post what I find.

 

I vote MAF. Disconnect maf and see how it runs

 

Coolant temp sensor ..............

 

You obviously have a timing light, check to insure you are getting spark advance when you ask for more RPM. I am guessing here but you should get about 36 degrees of advance at 3500 rpm. If you are not seeing some similar advance there is an issue in your EST system.

 

My first thought was TPS.

Did you check to make sure there was no sudden jump(s) in voltage readings when you tested the TPS using a digital volt meter?

The voltage numbers should slowly increase as you open the butterflies with NO sudden jumps and/or skips in the readings. Sudden jumps and/or skips means the TPS is bad.

Starting the engine at WOT puts the system into Clear Flood mode and turns off the injectors.

Jake

 

Thanks all for your inputs. I've been traveling and hadn't had time to touch the vette until last night. I bought the ALDL cable and using data master 32 software and an idle run found that the car stays in open loop from the beginning. I also have an Err 13 wich is O2 sensor fail for the DTC. The maintenance word confirms the same thing. At no time during the 3 minutes or so run, does the sensor fail go away. Wierd since its a new sensor (Bosch) left side only, seems to be connected right and gives ml voltage values between 350 and 560. Once or twice I have values in the low 600's.
The TPS voltage is spot on at .54 and good output to 4.0 + throughout the range. Spark advance changes from 25BTDC to as high as 40 or so. Knock sensor has activity, but I'm guessing it's not tremendous. I do have an ETS error code also, but I'm not sure how much stock to put into that.

Like I said it looks like the O2 sensor must be keeping me in open loop. What would cause a failed sensor and yet output normal ml values? and xcounts? The o2 sensor is mounted in open LT hedman headers, in the reducer (2.5") off the collector. There is no other exhaust at the moment. How long should it take for the O2 sensor to heat? Does anyone know where I can get the logic behind the faults IE this err 13 for the C-4? Thanks for the help.
BTW I do have the recorded file, and whenever I nurse the throttle to increase past 1600 rpm, the car just won't advance in power past the 1600.

 

I think you have a few problems.
how do you feel about your mother...........oh wait... different forum!

J/k

1. first, I think the coolant temp sender in the front of the manifold may have been installed too tight, ruining the calibration. That is what keeps it in open loop.
You need another CTS.
2. put the old oxygen sensor back in. If it worked before, it will still work, just don't tighten it too tight.
3. Fuel pressure may come into play. Your FPR may have gotten dried out and cracked, or fuel residue may have somehow restricted a port in the fuel rail to the regulator.
4. Your symptoms appear to be all fuel related. My 86 accelerates just fine in open loop.
Try checking the grounds at your fuel pump mount plate on the fuel tank.
5. try changing the fuel filter or pulling the pump and cleaning or replacing the sock on the fuel pump.
6. Just for grins, try unplugging the spark control module. it will go in limp home mode, but it may fix your rev problem.

 

Thanks coupeguy2001
The CTS gave me a steadily increasing value in my plots as the water temp rose, but I'll try it anyway.
The old Os sensor was trashed removing the old exhaust, so it's no longer an option. I am thinking of trying a new one, but I still dont understand the fail code if the output valtage is good and varies.
I do still need to check the fuel reg. I recently had the pump out and the filter sock was pristine. It was fine when I put it together and ran normally until I started this partial rebuild.
Do you mean unplugging the spark control module on the dist cap? if so which wire? I must be thinking of something else since I'm not sure it would even fire if no volts from coil etc.

Oh yeah about my mother...