I installed a speed-density TPI system from my 91’ GTA into my 94’ Suburban. The conversion is documented Here

The engine is a stock 350 for the Suburban. I tuned a stock AUJP bin to work with the truck engine. It actually required more fuel and a lot less spark thoughout the various load/RPM ranges. But for the most part the fuel table was not far off from the stock AUJP bin.

For a long time, it ran very well. But it has recently developed an intermittent stalling problem for about 2 weeks now. When it stalls during idle, it shuts down immediately, without notice. When it stalls during a steady cruise, it will jerk and sputter for a second or two, then shut down. There does not seem to be any pattern to the duration of run time before shutting down, or the time between episodes.

It does it at any temperature, ambient or engine. It makes no difference if the AC is on or off. Nearly each time it will restart immediately. However, it has started taking longer between restarts. But usually takes at least five minutes after the first start of the day for a stall.

Thinking it is either a fuel or spark problem, I did the following, in the order listed below:

• I suspected a clogged fuel filter, so I replaced it and added a can of Seafoam to the tank (last week). No change
• I installed a new distributor with all new components, including cap & rotor. No change
• I installed a new coil with the distributor swap. No change
• I installed a new IAC. No change
• I verified fuel pressure is fine and when it shuts down while idling, there is no loss in FP and the reading remains steady.
• I have checked for vacuum leaks, but have not found any.

And please note the following as well:

• The TPS was replaced only a month ago and is reading within range
• The fuel pump was replaced with a new AC Delco pump maybe 6 months ago.
• It is not throwing any codes.
• Spark plugs are maybe six months old, and plug wire are in good shape.
• MAP sensor is reading within range.
• VSS is working.
• Timing is adjusted within specification.

Since it is stalling at both idle and cruise, I do not think the EGR is a factor. Even though I have no codes, it would seem if the O2 sensor is bad it would not cause a stall as I have described.

The ECM is a 7727 out of a Corvette and is mounted under the hood. The original PCM is not controlling the engine, only the transmission.



Now I am beginning to think it may be the ECM. I noticed on the way home from work yesterday that when it cut out the volts displayed on my Auto-X-Ray dropped to zero, then came back up almost immediately. The engine did not stall, but it stumbled and jerked as before during this event.

Then it finally cut out and would not start for like a minute or so. During this time I noticed that my Auto-X-Ray could not communicate with the ECM. I checked the fuses and connections and everything appeared fine. When it finally restarted, it had communication and was reading voltage as normal.

I am considering getting another ECM, a remanfactured unit from Advanced Auto Parts. They range from $75 to $102

• $75 - 3 month warranty: Cardone
• $84 - 1 year warranty: Neihoff
• $102 - 1 year warranty: Borg Warner

Does it appear that the ECM is bad? Any advice concerning which ECM to buy? Any input is greatly appreciated.

Thanks, Ed

 

Sorry to hear of the problem.

Replacing the ECM sounds like something to try - if all your grounds and power connections
check out tight and clean. As you've been running for a while it doesn't really sound like
a wiring issue...


The ECM on my test bench (junkyard pull) developed a mental defect last summer. Replaced
it with a Cardone unit from Rockauto for ~$70. While it doesn't see a lot of use, that one runs
with no issues.


There are even discount codes around for Rock if you do a search - for example here's a 5%:

"This email is just a reminder that your RockAuto discount code will expire on May 16, 2006.

To take advantage of your discount:

- Please visit Auto Parts Fast at RockAuto and put the parts you need in the Shopping Cart.
- Use the following discount code:
391186278683
- If you are using our Java Catalog, enter your discount code (and no other characters or
spaces) in the "How did you hear about us" line of the shopping cart.
- If you are using our non-Java Catalog, place the discount code (and no other characters
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- Your discount will automatically appear, subtracted from your order total."


HTH

 

Thank you for the reply.

I bought a remanufactured unit this morning from Carquest for $75. I have friend there so I basically have a lifetime warranty. I will install it tonight and see how it goes. I sure hope this solves my problem.

Thanks, Ed

 

Looks can be deceiving. I discovered that my problem was NO voltage.

I replaced the computer and after 10 minutes it stalled again. It wasn't until then that I discovered no voltage to the ECM's fuse block directly after the stall. When retrofitting the TPI into the Suburban, the 7727 ECM needed a start & crank 12v source. I only found one wire under the dash that fit the bill, so I tapped into it using a clamp style fitting with a male plug.

The clamp must have wiggled loose and the intermittent stall was nothing more than random loss of power to the ECM. I ditched the clamp style tee for a more secure connection.

As embarrassing as this is, I am posting the result for closure to this issue.

The upshot is with a new distributor, coil, IAC and hooking back up the MSD 5 unit the idle is now smoother than ever before

Thanks for the input, Ed

 

That's a gottcha alright.

I bought one of those battery-powered soldering irons finally, for just such occasions.

It works (sometimes) in hard to reach spots. Based on my experience with boats, the best way
to approach an outdoor wiring situation is to crimp it, then solder it, then put on a little of that
liquid vinyl goop, then heat-shrink it. That seems to make a weather-tight seal that holds up even
around salt-water... at least so far.

Is that an MSD 5200 box?