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Stumbling, backfiring 1500-2000 rpm, Renix

AIbandit

NAXJA Forum User
NAXJA Member
Location
Chico, CA
87 4.6 renix stroker
Runs great at idle great above 2000. Only stumbles under load (uphill, quick accelleration)

Runs great with IAT disconnected (IAT reads correctly, tried a different one same thing)
TPS at 17% at idle. smooth increase all the way through throttle
MAP 27.5"HG engine off at 2300'.
O2 sensor replaced- no change
Dipstick grounds and firewall cleaned.
 
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Every time mine got that mid range bucking (detonation) it was fuel related. Might want to check your O2 sensor wiring.

One give away when something was wrong in my O2 sensor or circuit was mid range bucking (usually around 1400 or so while cruising and moderately accelerating) and then it would crap out again above 3500 RPM.
 
It doesn't stumble under load above 2000 RPM?

no once it gets out of that range it runs great.


I'll check my o2 wiring. It reads fine at the ecu though, atleast at idle.

Some notable crap regarding fuel delivery.
99 intake
H.O fuel rail (including regulator)
4 hole injectors
93 Throttle body bored to 63mm

Maybe the regulator isn't allowing enough in that range.

I was also thinking distributor index.
 
no once it gets out of that range it runs great.


I'll check my o2 wiring. It reads fine at the ecu though, atleast at idle.

Some notable crap regarding fuel delivery.
99 intake
H.O fuel rail (including regulator)
4 hole injectors
93 Throttle body bored to 63mm

Maybe the regulator isn't allowing enough in that range.

I was also thinking distributor index.

Check the dizzy indexing and monitor the O2 while this is happening.
 
What year ECU, O2 sensor and TPS does it have???

What fuel pressure is it set for, 49 or 31-39 with the vacuum FPR???

If it is a Renix TPS have you tested the IDLE to WOT voltages on both sides of it? One sde can be bad and the other good, causing the engine to bog down at WOT in too high a gear, like 1200 RPM at WOT in 4th gear at 15 MPH, LOL.

no once it gets out of that range it runs great.


I'll check my o2 wiring. It reads fine at the ecu though, at least at idle.

Some notable crap regarding fuel delivery.
99 intake
H.O fuel rail (including regulator)
4 hole injectors
93 Throttle body bored to 63mm

Maybe the regulator isn't allowing enough in that range.

I was also thinking distributor index.
 
What year ECU, O2 sensor and TPS does it have???

What fuel pressure is it set for, 49 or 31-39 with the vacuum FPR???

If it is a Renix TPS have you tested the IDLE to WOT voltages on both sides of it? One sde can be bad and the other good, causing the engine to bog down at WOT in too high a gear, like 1200 RPM at WOT in 4th gear at 15 MPH, LOL.

Ecu/sensors are renix.
TPS Checks out all the way through the range.


So my distributor doesn't have a fixed tie down like my spare and every one I see online. Though I'm 90% sure it's the one that came with my old renix motor.
 
Then it definitely sounds like the Dist needs indexing, Cruiser54 's link site has the blow by blow steps for it. Do not skip any steps, even a 1/16" off makes a huge difference. I strongly recommend making a cut away Dist Cap for nailing down the sweet spot precisely!!

Being off just a tad makes a huge difference, in spite of rumors that the ECU can compensate!!! Also need to make sure it is 100% dead on at TDC!!!
 
new distributor
sBEkuMP.jpg
 
Harmonic balance notch should be at 0 at TDC right?
I couldn't get to the 1 spark plug hole and get the balancer nut so I had someone else tell me when it blew. It appears to be incorrect.
 
Then it definitely sounds like the Dist needs indexing, Cruiser54 's link site has the blow by blow steps for it. Do not skip any steps, even a 1/16" off makes a huge difference. I strongly recommend making a cut away Dist Cap for nailing down the sweet spot precisely!!

Being off just a tad makes a huge difference, in spite of rumors that the ECU can compensate!!! Also need to make sure it is 100% dead on at TDC!!

Maybe my Renix is way more forgiving than yours. I actually installed my distributor one tooth off in each direction once just to see what happens. One direction, one tooth off and it was hard starting and when it ran it ran really bad. One tooth off the other direction and it ran pretty darned good. I tried mine set to spec and then moved it .030 each direction and it still ran well (enough). I even tried tuning by ear, micro adjustments of the initial rotor position.

If you have an after market cam or a really old (or new) timing chain, indexing is prudent.

The best (quick) way to find TDC, bend a slight curve into a piece of welding rod. Turn the motor over until it builds a little compression. Stick the welding rod on the top of the piston and feel when it goes all the way up, you'll feel when it starts back down again. It you go past the high spot back off a quarter turn on the balancer and try it again with the last movement to the right (facing the motor) to take up any slack in the timing chain. If done right, this is pretty darned accurate and you can even use it to double check your balancer zero. The whole process gets way easier with a little practice, the first time through it may seem awkward.

Or the quicker method turn the motor over until you build compression on number one then turn your balancer to zero, last motion always to the right so you take up the slack in the timing chain. You have to be a little careful it may build a very little compression on the exhaust stroke, not much, but it may fool you. On the compression stroke it will build much more compression. I always use a compression gauge, which eliminates any confusion.

Yours being a stroker, you may have an after market cam and/or a new timing chain and/or gear. So things may not be exact.

What you want basically is the number one piston all the way up on the compression stroke. The harmonic balancer mark lined with the zero. And both valve rockers completely relaxed, you can actually jiggle them sideways a little ( a few thousandths) with no push-rod pressure on the rockers.
 
Yours being an 87 presents a special set of issues. The timing of the OEM cam, the timing chain gear and rotor position was a little off from the factory. There is a TSB about this.

After market cams, timing gears, can present some special issues.

Your bucking being mid range doesn't indicate to me it being a valve train/distributor (rotor) issue, I may be wrong. The typical cure for mid range detonation is to retard spark, hard to do in a Renix. Next best is more fuel.

Sounds more like it is running lean and you are getting some detonation at mid range. In effect too much air and not enough fuel. Try unplugging the O2 sensor and see what happens. Try the stock TB again. Renix (and pretty much all 4.0 injected engines) run pretty close to the edge of detonation anyway.

Vacuum leaks can also be a contributing factor.
 
8Mud, lots of very good comments. Mine has 290,000 miles on the rig, may be the OEM timing chain on mine.

If that photo is at #1 TDC, then the the rotor is too far to the left.

AIbandit, you cut too much off the Cap, you need to keep the #1 pin on the cap, so you can see precisely where the #1 pin is located in setting the rotor. With it cut out, you could be off by a massive 1/4" on position.

At TDC, IIRC, the leading edge of the rotor edge ( Left edge) needs to be almost at the right edge of the #1 pin from the cap. Yours looks like it is at least 1/2" too far to the left.

My HB is aftermarket and has no notch for o* degree timing :( :rattle:

The Renix ECU is programed for a stock engine, so at WOT/acceleration in a mid range, it looks at a data table based on the stock OEM RENIX hardware, and or at the data from the O2 sensor telling it after the fact if the ECU made a good or bad guess on fuel rates and spark timing.

I think some people that put in strokers switched to an adjustable MAP sensor to fine tune the fuel rates???

But you should fix the Dizzy indexing issue first. Then make sure the MAP sensor has a solid vacuum seal end to end on the Vacuum hose line.

I think Old_Man has a stroker in his Renix, you should ask him!!!
 
After market cams, timing gears, can present some special issues.

Comp cam, replaced timing chain/gears (positive I did that right)
I'm on 41's

AIbandit, you cut too much off the Cap, you need to keep the #1 pin on the cap, so you can see precisely where the #1 pin is located in setting the rotor. With it cut out, you could be off by a massive 1/4" on position.

At TDC, IIRC, the leading edge of the rotor edge ( Left edge) needs to be almost at the right edge of the #1 pin from the cap. Yours looks like it is at least 1/2" too far to the left.

My HB is aftermarket and has no notch for o* degree timing :( :rattle:

The Renix ECU is programed for a stock engine, so at WOT/acceleration in a mid range, it looks at a data table based on the stock OEM RENIX hardware, and or at the data from the O2 sensor telling it after the fact if the ECU made a good or bad guess on fuel rates and spark timing.

I think some people that put in strokers switched to an adjustable MAP sensor to fine tune the fuel rates???

But you should fix the Dizzy indexing issue first. Then make sure the MAP sensor has a solid vacuum seal end to end on the Vacuum hose line.

I think Old_Man has a stroker in his Renix, you should ask him!!!
Damn I saw some forum image that showed cutting it like that.

I believe my renix reader can adjust the map but I haven't gotten that far yet.

Indexing is definitely priority right now, if it wasn't off before it is now :)
 
Off a tooth?
This seems to be as close as I can get it. I've gotten it further away on both sides.
wui7W4C.jpg
 
There's about a 1/8" gap between the rotor and the #1.
 
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It's on the wrong side of the #1 post. You need to move it to right side, then try for 1/16" gap is possible (based on mine, but timing chain may be a little worn) I had to cut the location ears of my Dizzy and rotate it to get it in the sweet spot. In that location in the picture, mine had low power and back fire-miss fired over 3000 rpm with a brand new Dizzy. The I found the photo/instructions (Cruiser54's maybe that said I had it on the wrong side).


The crazy thing is it runs, just not well that far off.
 
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