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Old 05-02-2006, 11:45 AM
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Intermittent Stalling Problem

I installed a speed-density TPI system from my 91 GTA into my 94 Suburban. For a very long time, it ran very well. But it has recently developed an intermittent stalling problem for about 1 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. This morning though, I tried to restart it and I had to wait about one minute. It ran for 10 minutes before shutting down again. It restarted immediately and I made it to the office without it shutting down again.

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 cap & rotor and coil. 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.

If it were a bad EGR, I would think stalling while cruising is not a symptom. Am I correct?
If it were a bad O2 (not throwing a code), it may run rough, but not stall. Am I correct?
  • 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.

I almost think I may have a very bad tank of gas. After removing the gauge last night, the gas smelled odd. But my wife has gotten gas twice since the first stalling episode. One reason I think this may be the problem is that when driving, if it sputters I can put it in neutral and rev it up and it will not stall. Or I can floor it and it will not stall. If it were a fuel or spark related problem (ex. Bad relay, module, sensor, etc.), it would seem that reving up the engine would make no difference.

Any ideas what else to look at?

Thanks, Ed

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Old 05-02-2006, 01:28 PM
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Quote:
If it were a bad EGR, I would think stalling while cruising is not a symptom. Am I correct?
Yes you are correct.

Quote:
If it were a bad O2 (not throwing a code), it may run rough, but not stall. Am I correct?
Correct again, I haven't seen a GM oxy sensor cause a dead stall.

I would suspect the ECM, (what ECM # do you have). GM had a big problem with there ECM's in those years. Try taping on the side of the ECM case, sometimes you can cause it to wig out if it is the problem.

I can assume that the new distributor came with a new pick up coil and module??

Is this a stock engine or is it modified?
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Old 05-02-2006, 01:42 PM
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Yes, the new distributor came with all new components.

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.




The engine is a stock 350 for the Suburban. I custom 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.

Since I have to visit a jobsite tomorrow, I can pretty much burn out what is left in the tank. I will put in some new gas and change the filter again and see if that makes a difference. Hopefully this problem will remain intermittent while I am on the road.

Any way to test the ECM?

Thanks, Ed
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Old 05-02-2006, 05:14 PM
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As I believe this is more of a question for the engine section ... I am moving it there ... so you will receive more views and possibly THE answer.
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Old 05-02-2006, 08:29 PM
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Originally Posted by 1931 steve
I would suspect the ECM, ...
Now I am beginning to think it may be the ECM. I noticed on the way home from work this afternoon when it cut out that 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 was fine. When it finally restarted, it had communication and was reading voltage as normal.

But no codes. Any way to check for sure if the ECM is bad, short of trying another unit?

Thanks, Ed
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Old 05-02-2006, 08:32 PM
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Edge, low voltage can cause the same problems. Can you monitor your system voltage with a volt meter? If so , you could see if there is an intermittent voltage problem. For grins, I would revisit all my grounds to make sure they are tight and sound and no signs of corrosion. A bad ground on my alternator caused me some stumbling early on with my Pro Flo.

By the way, I ended up with a Pro Flo 3503 in my coupe. It sure is nice. The only tuning I have done is reduce the Global Fuel by 6%. I played with the Global spark by going up 1% and Down 1% and it seemed to drop slightly in performance so I stayed with the preset settings. The 2barrel air valve on the 3503 is mis leading. It flows 750 CFM which is plenty on the little mild 327. I do kind of miss the Quadra Jet howl, but like the gas milage so far. I have driven 159 miles on less than half of a 14 gal tank.

Trees
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Old 05-08-2006, 01:31 PM
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Quote:
Originally Posted by trees
Edge, low voltage can cause the same problems.
How about 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 T-tap 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

Last edited by edge; 05-08-2006 at 04:17 PM. Reason: Found a picture of cheap T-tap connection
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Old 05-08-2006, 01:41 PM
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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.

In the trade, these are called "comeback connectors" for just this reason, . Most command start issues I have seen are directly caused by these things.
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Old 05-08-2006, 04:38 PM
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Just to make you feel better edge, I will share an equally embarrasing thing with my TPI. I was chasing down a weird problem of it the engine popping and acting wierd at a certain throttle position and above. I immediately suspected the TPS but was wrong. I chased down everything I could and tested every sensor. I come to find that there was a bald spot in the fuel pump wire. When a certain amount of throttle was applied (enough to move the wire), it would get close enough to the valve cover hold down to spark out, and cause loss of volts to the fuel pump. I had this problem for a long time and even posted frustrations.

I am glad to see you got it figured out .

Take care.

Dylan
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