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Trans/Power holding gear issues


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Okay this is going to be a long post.

1987 Pioneer

4.0 reman longblock

Renix closed cooling system everything new but heater core (burped and filled properly)

new aux fan (cycles on and work properly) 

New TPS, CPS and all sensors 

 

I have a new 4.0 reman longblock installed and AW4 trans rebuild. After getting it all back together and some tuning, properly index dizzy, vacuum lines sorted, O2 sensor, new cat and down pipe, new mts fuel pump/filter, fuel pressure is good, only get a random REM warning for Lean condition. Truck idles at 800-900 rpm, vacuum at idle is 14-18 and map is solid.  and will rev to the moon in park or neutral. Once in rpms will not go above 3k. For some reason REM isn’t reading trans information (need to troubleshoot with @NickInTimeFilms. Only issue I can find are some very slight exhaust leaks, muffler is fairly new but does have a krinkel in it from before the engine and trans work. Old motor had bad compression and a broken valve when opened up and had backfired really badly a couple time after muffler install. 
I have tried two separate trans computers and seem to get identical results.
 

I have done 90+% of @cruiser54 tips including the C1 delete. 
 

What are you guys thinking? 

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1 hour ago, cruiser54 said:

Have you tested actual fuel pressure? 


Yes fuel pressure was spot on, 32 at idle with vacuum connected and near 40 with vacuum disconnected. Before the longblock swap. I’ll try testing it again, but the MTS fuel pump and filter are less than 4 months old. 

 

All my REMII readings are good, ST fuel trim is a bit high, but not crazy. 
 

Best description I can give is once in gear the truck reaches 2500 rpm and won’t climb above 3k after it shifts into 3rd or overdrive. In 1/2 it will, I definitely still have some exhaust leaks and am addressing those. 

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1 hour ago, Pete M said:

shouldn't the idle be a bit lower?

Are you saying my sitting idle should be lower?

 

 At 50mph ish I am showing just under 2k. I am running 32inch tires and 3.55 gears, so I know she’s not going to be a speed demon. 

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2 hours ago, Pete M said:

someone needs to actually check to confirm, but I think idle should be more like 700-750. 

I readjusted idle to 750-800 didn’t make a big difference. Also took advantage of the truck being cold this morning to burp the cooling system (rear temp sensor). Temp is good running right at 200-210 (via REMII) when warmed up. Temp gauge on my cluster doesn’t work. Aux fan operating as it should and I am running a 195 thermostat.

 

Tightened exhaust manifold bolts and best I could and tightened down pipe collector as much as I felt safe. Seemed to help exhaust leak. 
 

Went back through all the C1 delete splices and re-solder them. Found a few that were not as tight as I would have liked. I’ll be going back through all the other splices I had fixed before the longblock install. Mech that did the install wasn’t very careful with wiring. 
 

Now getting ready for TS FREDS impact. Hopefully it won’t be much more than some rain and wind gust since we are just west of the predicted landfall area.  
 

3 hours ago, Ωhm said:

Make sure you got full swing on your throttle plate or its not loose, in the throttle body. You'll need to look. Could just be a mechanical issue.

Throttle plate is good and moves through the full range.

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  • 3 weeks later...

So I finally got around to testing the fuel pressure again. At idle it sits right at 36 with vacuum line attached and bumps up to 40 when vacuum is disconnected. Here's where it gets strange if i disconnect the vacuum line and plug both the regulator side and intake side the the truck idle is more stable and the truck actually seems to run better. 

 

I have double, triple and quad checked all the vacuum lines, wiring, tps, cleaned the throttle body/IAC, and have a new (2weeks old CPS) instaled. I am having to push the gas pedal to the floor to accelerate when in gear. TPS shows mid to high 70's during acceleration. Once to speed 50-60 i have to keep 3/4 or more pedal to maintain speed and i have no kickdown when stomping on the gas. Trans was rebuilt and I've tried two different trans computers. Any thoughts?

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1 hour ago, CGCWO said:

At idle it sits right at 36 with vacuum line attached and bumps up to 40 when vacuum is disconnected. Here's where it gets strange if i disconnect the vacuum line and plug both the regulator side and intake side the the truck idle is more stable and the truck actually seems to run better.

 

At IDLE disconnecting the vacuum source to the Fuel Pump Regulator will increase the pressure (PSI), on the fuel, at the tip of the Injectors. Using your example 40-36=4psi additional PSI of pressure on injectors at IDLE. Spec would be 39-31=8psi additional pressure. Difference here could just be the pressure gauge you're using.

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Thanks for the info and confirming I am close to spec for fuel pressure. I absolutely believe the difference is due to the gauge I am using. 
 

Still trying to figure out the problem with having to use close to or full throttle to get up to speed and the kick down (passing gear) not responding. 

15 minutes ago, Ωhm said:

 

At IDLE disconnecting the vacuum source to the Fuel Pump Regulator will increase the pressure (PSI), on the fuel, at the tip of the Injectors. Using your example 40-36=4psi additional PSI of pressure on injectors at IDLE. Spec would be 39-31=8psi additional pressure. Difference here could just be the pressure gauge you're using.

 

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Update…found the mech that did my longblock swap connected main ground to the alternator bracket (of course this is aluminum). Rerouted directly to the side of the block, found a broken three prong connector to the coil, refreshed all engine compartment grounds. Reset TPS and swapped back to original trans computer she’s shifting and running like a bat out of h3ll now!!!!
 

Maintains speed and gear with 1/4-1/2 gas pedal. 
 

Thanks for all the advice and ideas. I knew it was going to be something simple. Not 100% sure it was one of the grounds, tps or the trans computer. Pretty sure the ground to aluminum was a part of the problem. 

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