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Old 11-26-2007, 10:56 PM
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Default 350 TBI Problems & Questions

tbi nI'm helping a guy here at school, it's an '89 K5 Blazer w/ TBI-350/700R4.

Brand new ~$2,000 350 crate engine with an rv-cam in it. Throttle body spacer (I know, they're worthless). Also has headers. New distributor (assembly), cap, and rotor. Also has 4 core radiator and electric fans.

Cam is an Elgin Pro Stock: E-923-P
Specs: Elgin Industries : Online Catalog

As far as I know the PROM/ECM is stock. What it's doing is starting and idling fine, if I ease onto the accelerator it revs fine. If I hammer it, it stumbles bad. From idle, put it into R, it stumbles and dies. From N put it into OD (or anything) stumbles and dies. If I keep the rpm up a bit it won't stumble and die. Engine also heats up rapidly.

This is the one error code:

CODE 42

Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system.

During cranking, the timing is controlled by the ignition module while the ECM monitors the engine speed. When the engine speed exceeds 400 RPM, the ECM sends a BYPASS signal to the ignition module which switches the timing to ECM control. The ECM calculates what the timing should be then "tells" the ignition module via the EST circuit.

An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be re-started but it will run on ignition module timing.

The conditions for setting this code are:

* System in BYPASS mode but the ignition module is still controlling timing

- or -

* Engine speed > 600 RPM with no EST pulses (ECM controlled timing) going to the ignition module for 200 msec.


Typical causes for this code include:

1) BYPASS line is open or grounded
2) EST line is open or grounded
3) PROM or CALPACK not seated properly in the ECM
4) Poor connections between ignition module and ECM
5) Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise)
6) Faulty or incorrect ignition module
7) Faulty ECM


So...I'm looking for a definitive yes or no on whether or not the rv-camis fubaring the computer. If not, what else?
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Old 11-30-2007, 01:46 AM
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Hot , 44 views and zip-****-nothing for replies.

This was ordered for it:


A local parts shop with an owner who has a predilection for Chevys strongly urged the owner to get a custom PROM made up for it, so he'll do that too. We'll go from there.
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Old 12-20-2007, 03:46 PM
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yup, prom needs to be changed. these guys have helped me i nthe past Affordable Fuel Injection - Affordable Fuel Injection you might check with them. they seem to know their stuff. they sure know more than i do.
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Old 12-21-2007, 12:13 AM
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Thanks u4ia4, the guy still needs to get a chip. That new MSD dist made a world of difference, it'll actually run down the road and shift without dying now. A chip will just finish the job.
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Old 12-21-2007, 08:02 AM
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yup, it does make a big difference in these "new fangled" vehicles. The way I figure it...if you've got to tuen a carb after every modification, then a PROM is about the same. of course the computer can handle some of the modifications, but it can only do so much.

Good luck
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