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1990 renix fuel problem

P

pmartinez

NAXJA Forum User
Location
nor cal
I have a 1990 renix that was just overhauled, new head, rings,rod and main bearings, oil pump, water pump, radiator, cps,tps, map,plugs cap rotor. Before it was overhauled it was running rich at idle.Now after all of these parts it still runs rich. I have a 1989 renix that I have swapped all the sensors back and forth from one to the other. The 1989 runs fine but the 1990 still runs rich. I have even swapped out the ecm.But still the same. My question is does anyone know what would cause this thing to go full rich at idle. Once you drive it down the road it runs good anything over 1000 rpm and it will clean up pretty good. It doesn't matter if its hot or cold. ANy help would be great. Thanks, Pmatinez.
 
fuel pressure regulator? Pull the vacuum line and make sure you don't have fuel coming out of it.
Check your pressure at idle and at speed.

Nick
 
Fuel Pressure Regulator isn't getting the vacuum signal from the intake.
Fuel Pressure Regulator not functioning (bypassing excess pressure to return.)
HEGO failed, ECU skipped into Open Loop mode (which runs awfully rick - around 13.0:1, IIRC.)
HEGO wiring failed, not passing signal.

I'm assuming your "all of the sensors" includes the primary sensors for fuel metering with RENIX - MAP, IAT, and TPS? TPS properly adjusted? Never hurts to verify, y'know...
 
There is one sensor no one ever mentions that will cause it to run rich. It is the air charge temp sensor. It is mounted on the intake manifold just to the rear of the throttle body. Surprisingly enough they go bad quite frequently.
 
Last edited by a moderator:
Yes ALL the sensors were changed over. The fuel pressure does go up with the vacuum line removed from the regulator. But I haven't swapped it with the one on my 1989. So maybe I will try that next.
 
old_man said:
There is one sensor no one ever mentions that will cause it to run rich. It is the air charge temp sensor. It is mounted on the intake manifold just to the rear of the throttle body. Surprisingly enough they go bad quite frequently.
Click to expand...

I mentioned it (IAT,) but didn't cover it in any detail.

The primary IAT problem with RENIX is that the sensing tip gets crapped up with carbon from the EGR system - and it can't often be cleaned off.

And people wonder why I don't like the EGR idea...

(@Tom - I didn't edit your post - I just hit the wrong button. Sowwies!)
 
pmartinez said:
Yes ALL the sensors were changed over. The fuel pressure does go up with the vacuum line removed from the regulator. But I haven't swapped it with the one on my 1989. So maybe I will try that next.
Click to expand...

So, you have approximately 31 psi with vac/39 psi without vac at the rail?
 
pmartinez said:
I will put the pressure gauge back on and will post the pressures.
Click to expand...

Good. Failed pressure regulator mode is normally higher pressures, so we need the numbers.
 
Swapping the sensors from a 89 to your 90, including the ECM, and the problem remains.

That indicates a open in the wiring harness from the IAT or something - good part or not, the computer isn't getting the signal.

Checking the continuity of any suspect wire from sensor to the plug may discover the problem, and I don't envy you the job.
 
How do you know it's running rich? Was this why you rebuilt the motor? Who did the rebuild (you or a shop)?

Since you have spares to try swapping. Could try the injectors. Also carefully check all of the harnesses in the engine bay for kinks, pinches or cuts.
 
The egr is working,that I know. I also changed the injectors with the ones out of my 1989. I rebuilt the engine myself. I am a diesel mechanic and have been in the field for 26 years. It is running rich without a doubt black smoke at idle. I will put a pressure gauge on it tomorrow Have to go to work and get my gauge.
 
So the fuel pressure is good but you are running way rich.

What thermostat are you running? If you run less than the 195 you will run rich.
 
joe_peters said:
So the fuel pressure is good but you are running way rich.

What thermostat are you running? If you run less than the 195 you will run rich.
Click to expand...

Not necessarily. I've pulled the operating temperature of my 88 down to about 195 with no ill effect on fuel economy and no ill effect on emissions.

If pressures are good, I'm leaning toward a sensor issue - MAP, TPS, IAT, or HEGO (the first three are basic inputs, the fourth is a feedback loop trim.)
 
Did you also swap out the coolant temp sensor on the block by the pass side motor mount?

If you did, I suggest you go back to the basics. Check each and every sensor using a multimeter (forget swapping), and verify each sensor is function properly.

Also check the big connector on the firewall. Make sure all of the contacts are clean.

Next, you may need to start checking the harnesses to see if there are any breaks/shorts.
 
Couple other things to check:
If a vacuum hose comes off of the EGR control thing that is mounted in the inside fender by the air cleaner, it will run rich.
So will a bad O2 sensor.
Good luck.
 
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