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Sporadic dip or surge in idle


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Fingers crossed on the intake temp sensor. I ordered the GM one recommended by Ohm and it’ll be here Friday. Picking up a tap set. Do you recommend taking the throttle body off to keep shavings out of the manifold? Or does the manifold need to be taken off for the install?

 

anyone have a renix butterfly valve stopper bolt they would sell? It seems that renix jeeps don’t make their way down to Durham NC junkyards. I'm going to measure my valve gap with a spark plug gapper to try and get it to 0.004”. I’m thinking of just adjusting the bolt by grabbing the extruding part of the bolt with a wrench and rotating. I’d like to get a new one, but thinking temporarily. 
 

 

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15 hours ago, cruiser54 said:

They rarely fail and are easily tested. 

 

I've got a bunch of them. Used

 

15 hours ago, PhilisDiller said:

what’ll you let one go for? 
I just double checked and it is a 1/4” NPT.

 

 

1 hour ago, PhilisDiller said:

Fingers crossed on the intake temp sensor. I ordered the GM one recommended by Ohm and it’ll be here Friday. Picking up a tap set. Do you recommend taking the throttle body off to keep shavings out of the manifold? Or does the manifold need to be taken off for the install?

Myself, I'd deal with @cruiser54. Wouldn't want no metal filings in my intake manifold unless you remove and steam clean it.

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I tapped my intake and swapped in the correct sensor. I made a nifty contraption that utilized my brake booster vacuum line, a random brass pipe fitting, a cut up beer can and some tape attached to the shop vac nozzle to ensure no shavings could get past.The temperature is now correct - ambient air temp when cool and stupid hot heat soaked air when hot - just as the engineers designed it. 

Also, I looked at my ECU to make sure i had the correct one and found that this is a remanufactured ECU. IDK Who remanufactured it but it looks pretty new. See attached image. 
 

i went through and retightened my intake/exhaust bolts/nuts. They were all snug, but I got a 1/8 turn out of some of them.

 

overall, the car doesn’t run any different. I took a long video of me driving around today and it’s really interesting watching the O2 sensor. It’s acting quite strange. The O2 reading after warming up was around 0.4v. while driving around at lower RPMs it stays pretty constant, but when doing heavy acceleration, the O2 starts fluctuating between 1 and 4. When I let off the throttle and fuel is cut, it reads a 4.8v. So it is able to sense the fuel cut immediately, but seemed to be finicky about when it wants to have the O2 swing. Watching my video again, it seems to only want to swing when it’s in closed loop driving and ST is bouncing around the low 10-50 range, but it also sometimes doesn’t bounce at ALL when in closed loop. 
 

you can see in the video - at 6:10 that as I’m accelerating in closed loop, the o2 doesn’t start swinging until the ST is quite low and then when I let off the throttle to shift the ST goes back to 128 and the O2 stops swinging. As the ST drops below 50 the O2 starts swinging again. During this time I have relatively constant throttle and driving conditions and you can see my duty cycle drop from 17% to almost 13% before the O2 levels are  lean enough to be registered. It seems like the O2 is just stuck reading stupid rich until the fuel is trimmed a bit to be within more normal A/F ratios. 
 

Makes me think it’s getting way too much fuel. I even double checked my Injectors were opening/closing properly by placing a screwdriver tip against the body of the injector and the handle up against my ear. Can hear the little ticks on all them. Fuel pressure again is 31/39. Any chance these injectors could be knockoff ebay injectors? I’ve attached a photo.
 

 

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I ordered some remanufactured Bosch 746 injectors that will be here next week. The ones that are in there now are no-name 700 injectors. my hope is that the no name 700s are just junk, because it seems like the difference in these two units are negligible. Is there a reason why 746s are the go to injector to install, but not 700 or 710 from the fords? I've seen a few people installed the 710s, but I keep hearing that 746s are the way to go even though they seem similar enough...

 

Also, pardon my ignorance, but how does the resistance difference between these two injectors impact the performance?

 

b0280155746.jpgb0280155700.jpg

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1 hour ago, PhilisDiller said:

but how does the resistance difference between these two injectors impact the performance?

 

Let me try and make a fool of myself here. Difference in ohms determines current flow. Current flow through INJ coil determines magnetic strength. Magnetic strength determines the UP/DOWN, ON/OFF for the slug within the INJ. I do believe that the INJ must be a match set with the INJ driver mounted on the ECU. Remember I can justify anything to myself.

 

Assumption: Different INJs solve your problem.

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@Ωhm I like the explanation! I hope the different injectors solve my problem too. 
 

does anyone know what the specs of the OEM injectors on an 87 4.0 are?

 

edit - the renix FI manual says it should have 16 ohm resistance. Well looks like The ones in there currently are definitely not 16.  I just hope I haven’t fried anything on my ECU yet with the different resistance. It’s a remanufactured ECU already. I wonder what f’ed up the old one...
 

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So I received the injectors and installed them today... she can maintain closed loop at idle now! Still not perfect though because the ST has to drop down to 10-30 to maintain idle. The swings in o2 voltage are a bit long... I haven’t taken her for a drive yet but I’m happy i made some progress. Can Anyone make sense of why I’d be at the ST level? 
 

ive attached a video of her idling where I had warmed her up already and then shut her off. I reset the LT to 128 by holding the battery cables together. The video I took is right after I started her while warm and was still in open loop. 
 

 

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"Better VAC,      hell ya"

 

9 minutes ago, PhilisDiller said:

Can Anyone make sense of why I’d be at the ST level?

746 INJ's I believe delivers more fuel so STFT needs to cut back on INJ PW time (mS), but well within the Range of Authority for the ECU to control.

 

3 minutes ago, cruiser54 said:

Go drive it!!!

:yeahthat: 

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Mine will drop like that also if my battery gets disconnected. I also have the 746 injectors. After a nice long drive it learns the injectors and the ST stays around 90. After that everything works correctly.

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Hahaha it was dinner time with me lady, so that took precedence. 
 

well, I took her out for a spin and it looks like it’s able to maintain closed loop decently while cruising at a steady speed and throttle. But if I am going up or down in speed, a lot of the time it fails to keep closed loop. 
 

Also, it’s now failing to keep closed loop at idle again... I can see right as ST is approaching 0, the o2 sensor start to swing but it’s too late and it fails into open loop.

 

okay, since my fuel pressure is good, the issue shouldn’t have anything to do with my fuel pump right? 
 

I am going to try and reindex her tomorrow, but other than that I’m stumped...

 

I know I post way too many videos, but this little REM is helpful and I had me lady take a 2 part video driving with and then I took another one idling after the drive (Don’t mind my comments at 30 seconds on the idle video. I forgot open loop was 6.9mS pulse width before the drive too.)
 

 

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15 minutes ago, JMO413 said:

Mine will drop like that also if my battery gets disconnected. I also have the 746 injectors. After a nice long drive it learns the injectors and the ST stays around 90. After that everything works correctly.

Good to know! I’ll have to take her for a long cruise on the Highway then. I can get some mpg numbers too for reference. Just got to get temporary registration... been test driving her around with a farm plate. Haven’t tried registering/emissions yet, knowing I’ll fail. 

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Idle after the drive video:

Engine VAC at idle hovers around 16.2-15.9"hg (should read 18"hg and above). Your VAC reading tells the ECU to add fuel or increase INJ PW time.

 

If you can, get a mechanical vacuum gauge and see if it correlates with your REM VAC reading. Like a MAP test.

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Hey all, I cut the window in my distributor to index it and it looks like it’s waaaaaay off. Almost 180 degrees off. See picture 
 

I wanted to verify exactly what top dead center should look like. I can’t fit my finger over the spark plug hole to feel the pressure from the cylinder, but through the spark plug hole I can see the top of the cylinder rising up as the timing mark on balancer approaches the 0 mark.
 

Here’s my issue, as I’m watching cylinder#1 rise, it actually reaches true TDC when the balancer mark is between the 10-12degree mark. As I continue to rotate the crankshaft bolt clockwise towards the 0 degree mark, the cylinder actually travels downward a bit. Is this normal? I thought true TDC should be when the crank balancer mark is at 0? 

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I’m not sure why the photo is upside down. It’s right side up on my phone when I upload it.  

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Okay I think I answered my own question. It was at TDC exhaust stroke. I did another rotation to compression stroke (hence the pressure test) and as expected I’m still 10-12 degrees off. It’s more like 12 degrees. 
 

The trailing edge of the rotor is lined up perfectly with 1 when it’s at the 12 degree position. My guess is the PO already indexed it.

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23 minutes ago, cruiser54 said:

Not .020" past?

I’m not sure what you mean here. I didn’t see anything in the write up about it being .020” past. 
 

I checked the rotor at the 12 degree timing true TDC and the trailing tip of the rotor lines up exactly with the beginning of the spark 1 metal piece. 


with the degree timing mark set to 0, the trailing tip of the rotor is lined up at the middle of the spark 1 metal piece.

 

I don’t understand why my 0 crankshaft balancer mark wouldn’t line up with true TDC... is it possible the PO messed with the timing or is this normal? Everything I’ve read leads me to believe it should be 0 when at TDC

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12* is not true TDC. It's possible that your harmonic balancer is failing and the outer ring has moved. 

 

From the write-up:

 

  1. Reinstall the distributor cap with the cutout “window”. Rotate the distributor housing until the trailing edge of the distributor rotor tip is just departing from the #1 spark plug wire post terminal .
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Ah dang, is there a reliable way I could tell that it had slipped before I buy a new one? Looking at the mopar 33002920AC and they are about $130. I need to reference the fuel injection manual but I thought it used the flywheel teeth to determine timing. so aside from a risk of the harmonic balancer failing, am I wrong in thinking that a slipped harmonic balancer shouldn’t be causing any of the issues I may be having?

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I just confirmed true TDC using a screwdriver and got an average mark between the marks I made with the screwdriver maxing out both CW and CCW. The notch in my harmonic balancer is at 20 degrees. 
 

there’s nothing else that would cause it to be off that much right? It’s gotta be the harmonic balancer

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