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TBI 454 runs like crap when hot

MTBLAZER89

MTBLAZER89

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TBI 454 pretty much stock rebuild. The motor runs pretty good cold with just a random noticeable miss at idle which seems to go away as it warms up ~2-3 minutes. Throttle response is good and everything seems fine until the motor gets up to ~200* then it develops a decent miss which is considerably worse under a load.

Towed with it a couple weeks ago and it seems fine running down the road, but if i stop getting going again the motor misses horribly and has very little power. How bad it runs seems to be directly proportional to how much of a load is on it. Normal driving it misses, but if you apply enough throttle it still moves pretty good.

I had this problem once with a code 45. I ruled out the MAP and changed the cap plug and wires. I also fixed a broken fresh air vent line on the driver side valve cover. Seemed to run fine for a long time, but the problem is reappearing. :confused:
 
Sounds like ther Distributor module or magnetic pick up coil to me. Both will will usually start acting up after the motor gets warmed to operating temp. The dist mod usually wont throw any codes except the usual 12. Sometimes the pick up coil will throw a 42.
 
Check the CTS (coolant temp sensor) this is the one the ECM uses to know how cold/warm the engine is. If the engine is up to operating temp but the CTS is telling the ECM that the engine is cold or vice versa this will affect how the engine runs.
 
Well it looks like its about $7 at Autozone so I'll just replace it. Intake gasket is getting done on Mon, and maybe the TB gasket as well.

Scott I saw a link in your post once for a TB riser and injector riser both to increase TBI performance, but they were for a 5.7. Do they have those for the 7.4? Not a TB spacer, but the ring that the air cleaner sits on I believe.
 
MTBLAZER89 said:
Scott I saw a link in your post once for a TB riser and injector riser both to increase TBI performance, but they were for a 5.7. Do they have those for the 7.4? Not a TB spacer, but the ring that the air cleaner sits on I believe.
Click to expand...

Everything that works on the 350 TBI is the same for the 454 even though they spec a different part number for the injector pod spacer. I am running the 350 injector pod spacer on my 454 TBI. The velocity stack spacer also is the same for any TBI or 4bbl carb.
 
The injector pod spacer moves the injectors up out of the TBI about a 1/4" which helps to increase airflow. The velocity stack is a definate help as it does 2 things at once, it raises the air cleaner assembly higher (more velocity) and since you have to cut the bottom side of your air cleaner for the much larger diameter mounting surface of the velocity stack (because of the "salad bowl" shape) which directs airflow much better than an abrupt 90* turn down into the TBI of the stock set-up.
 
X2 on the velocity stack. It really helps build torque sooner in the rpm band.
The stock air cleaner spacer does nothing but restrict and clutter up the air flow.
 
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