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94' 454, my ignition timing story

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When traffic light turns green, I kicked the throttle pedal, finally, this time, I got the power that a 454 supposed to give me, I almost cried.



1994 Chevy Suburban Silverado K2500

454 L19 TBI


153K miles


Months ago, I posted several topic (2 or 3) about it stall and knock sound under the floor, while cruising on highway.

Well, the "highway" include GGB (Golden Gate Bridge).?

94' 454 stall while driving and knock sound under the cab

94'454 stall again, after change fuel pump


Take note that I am actually completely a newbie, new driver (2 years), new vehicle owner, and new to America.

So maybe some thing in my topic is wrong, but I don't tend to misleading.


Shattered catalyst


After the GGB stall, I found its power is weaker than before, and sounds like the exhaust is blocked, and when drive next to a vehicle or wall, I can hear air bleeding sound.

Then got MIL code 32, EGR, however I can't find any problem on EGR system. This 454 engine use Linear EGR system, the valve is controlled by ECM directly, no vacuum pipe. 

I tried to remove air filter, to make it performs better, then find the blocked-exhaust sound become louder.

Then one day the stall happened again, I found the knock sound sounds more like opening a soda can.

So I visited a muffler stop, turns out the catalyst is shattered, quite big loss. ?

Since I don't have enough money for a catalyst, and it may be shattered again, so I asked them to put a steel pipe instead as a temporary manner.

After that, the compressed air sound is disappeared, the blocked-exhaust sound is lighter but still there, and the performance is better but still weak.

      So shattered catalyst blocked exhaust, caused air bleeding sound.

      And caused extremely high pressure in EGR system, too much exhaust injected into intake manifold when EGR is open, caused ECM think EGR have problem, light MIL and sending code 32.


Fired chip in ICM (ignition control module )

The last time it stalls, at a quiet place, I finally figured it out that it feels and sounds like wrong timing, and when press throttle pedal, it back fires, and the harder press the pedal, the louder the sound is, very loud. And when it back fires, I can feel shock on throttle pedal.

I told this to my mechanic, he told me to replace the ICM. He said back to old days, he replaced many of it.  He suggested me to purchase new one, because it's cheap, even from ACDelco, and this thing usually break down for years parked vehicles, vehicles in junk yard usually parked for years.

I opened the metal cover of old ICM, find one of chips is black, oil or something around it is dark brown, the metal cover supposed to be glued to the plastic shell, but the gap near the black chip is open, so it's clear that the chip was exploded.

After I changed the module, 3K+ miles so far, including 2 round trip from San Jose to Yosemite, stall never happened, I think the stall problem is officially solved.

      So the broken ICM caused wrong timing, and stall.

      "Knock sound" is actually backfire, the exhaust is under floor, so I felt it's knock sound under floor.

      Back fire caused huge pressure burst in exhaust, then transferred to intake manifold and throttle body via EGR system, caused shock on throttle pedal. Thank god this didn't ignite the gas-air mixture, or my trouble gonna be bigger.?


Wrong base timing

That's NOT all folks!

I found it still very weak, on I680, the climb at east of Fremont, it even can't maintain 60MPH!  WTF??

At this time, what I have done on it:

    Fueling system:

        New Delphi fuel pump, capable of over 60PSI;

        New fuel filter, ACDelco;

        Fuel injector, tested and cleaned;

        Fuel pressure regulator, changed new spring, 30PSI;

    Air intake system:

        New air filter, ACDelco;

    Ignition system:

        Distributor cleaned;

        New ICM, ACdelco;

            Full assembly of distributor and ICM from junk yard as spare part.

        New spark plugs, wires and ignition coil, ACDelco.

    Cylinder pressure: I forgot reading, but within normal range.


I pulled out the distributor for cleaning and ICM change reason, but when I put it back, I tried to find the timing mark. However, only engine block have the mark, the distributor don't have mark from factory, only a mark made by the ex-owner's mechanic, and it turns out it's wrong.

So I tried to do base timing. I borrowed ignition timing light from my mechanic. But I can't find the "timing connector". At that time, I thought cold start and idle is running at base timing. So you guess it, runs over 20 degree ******.


Then one day, I read my shop manual carefully, find out cold idle is NOT base timing, and only when the "timing connector" disconnected, the engine runs at base timing.

However I can't find the connector, then after some dig on internet, I finally find it: inside the cab, passenger side, by the side of the blower motor, a single pin connector, tan with single black stripe lead, that's it. It's a bit far from "adjacent to the distributor".?

Then I borrowed the timing light again,  do the base timing, hit the road again, the result, on I680, maintain 70MPH easily, like I write at beginning of this topic, I almost cried!

Just recently days, it  even reached over 90MPH when climbing! Yeah it's speeding too much, but you know the traffic flow on highway is a bit crazy after reopen, probably due to people lock in their home for too many days.




So That's all folks, I currently focus on renew my truck camper, including solar panel, painting, bathroom convention, jack system rebuilt, then maintenance on the 1996 Ford F250xl, 350 engine, and convert to dually, create a "FAKE F350". ?


Then come back, I found the A/C compressor is dead, my mechanic suggested me to get one from junk yard, because most of them from car part shop are rebuild in China, you know what, even I am Chinese, I always avoid "China".?


Edited by Tom_1991
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On 6/27/2020 at 6:09 PM, CamGTP said:

Yeah, that's quiet the story for sure. Lots a little things can surely make it run poorly, at least it's all fixed up and running good now.

In fact, I've already expect something would happen, it's in very good shape, only 150K miles, but only sell $1750.

While other sellers on Craigslist, I remembered a 1995 C2500, bad paint and lost the 3rd row of seat, dare to price over $4000.

I have seen it on Craigslist for about 1 month, the SMOG check is 3 months ago, and their signature on title is 6 months ago, they have tried to sell it for long time.

But my mechanic is 100% sure there is no big problem, just buy it, it's a good deal.

He knows this engine very well. His shop used to serve American vehicles, but now mainly bodywork and Asia's mechanic .

I think I am very lucky to know my mechanic.

Edited by Tom_1991
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