My 99 vortec 5.7 STINKS, has a subtle miss but no Codes or CEL

Reading further in the thread....

If the exhaust system temps are highest at the exhaust outlet, that seems to me to indicate raw fuel being dumped out of a cylinder. It's too rich to burn, and once that cylinder's contents are exhausted out the manifold that raw fuel continues down the exhaust system without burning due to the fuel air ratio being too far off (rich). Instead it evaporates and cools the exhaust system, but heating up itself, past the combustion temperature. Once it get's near the tailpipe, the extra oxygen available there lets it ignite in the tailpipe.
It's essentially turned into a Ford diesel doing a re-gen and turning the tailpipe into a flame thrower.

Earlier in the cycle of this failure, the amount of raw fuel being dumped was less and in that case it was able to burn once it mixed with the other exhaust, likely in the cats, cooking them off and making the funny smell.

IMO this truck is heading for major mechanical damage, if none has been done already due to lack of lubrication (thin oil) or over temperature exhaust. The cats are likely done. Something is leaking fuel at an increasing rate, and eventually you could face a huge backfire in the cylinder or manifold. One that could do serious damage. Even break a crank.

The symptoms and progression of this issue are almost identical to CSFI failure where the injector poppet gets stuck further and further open until it's open a lot, and all the time. leaking fuel into the cylinder. The engine will run rougher and rougher until the big badaboom.

Tachyon said:

Reading further in the thread....

If the exhaust system temps are highest at the exhaust outlet, that seems to me to indicate raw fuel being dumped out of a cylinder. It's too rich to burn, and once that cylinder's contents are exhausted out the manifold that raw fuel continues down the exhaust system without burning due to the fuel air ratio being too far off (rich). Instead it evaporates and cools the exhaust system, but heating up itself, past the combustion temperature. Once it get's near the tailpipe, the extra oxygen available there lets it ignite in the tailpipe.
It's essentially turned into a Ford diesel doing a re-gen and turning the tailpipe into a flame thrower.

Earlier in the cycle of this failure, the amount of raw fuel being dumped was less and in that case it was able to burn once it mixed with the other exhaust, likely in the cats, cooking them off and making the funny smell.

IMO this truck is heading for major mechanical damage, if none has been done already due to lack of lubrication (thin oil) or over temperature exhaust. The cats are likely done. Something is leaking fuel at an increasing rate, and eventually you could face a huge backfire in the cylinder or manifold. One that could do serious damage. Even break a crank.

The symptoms and progression of this issue are almost identical to CSFI failure where the injector poppet gets stuck further and further open until it's open a lot, and all the time. leaking fuel into the cylinder. The engine will run rougher and rougher until the big badaboom.

Click to expand...

Hey thank you for the reply and your input! Regarding the rear o2 sensors, they have not been removed per se but have been given a static value that Black Bear felt would be good which I believe was .45v but I would need to confirm. It was about the middle of normal cycles. So no other tuning that removes anything was done other than that static voltage on the rear o2s.

With the idea of leaky injectors, I dont really understand how this system works in depth. Could you help me understand these questions?

1. Does a leaky injector leak all the time or just when the engine is running? The reason I ask is because it did hold pressure down to 20 psi at hour 13 and stayed at 20 for 11 more hours. Is that a bad drop, normal, etc.
2. Would a injector leak because of incorrect voltage supplied to that injectors pin or is it more of a mechanical failure? I ask because I wonder how I can troubleshoot that, if I can measure for voltage or resistance or something on the wiring going to the injector plug?
3. Would a cylinder that had a leaky injector cause the spark plug to look different than one on the same bank that was not leaky?
4. Any other ways you can think of that would help me narrow down or confirm a leaky injector on a cylinder?

The new oil it has been running has a slight smell of gas but not near as strong as the oil I pulled out of it after it had the spark plug wire shift and touch the header until it arc'd bad enough to cause a misfire code on that cylinder (my wife was driving it while I was out of town so thats all I could tell on my call with her).

Well I did get some good news today. The shop that rebuilt my engine is going to get a new acdelco mpfi unit shipped to me and they will worry about the warranty themselves later. I have moved to another state since the rebuild early this year so they are calling to see if the labor can be warrantied since it was installed by a professional shop that I cannot take it back to now because of my move.

So if the labor won't be covered, any idea what it would cost roughly for install on such a part?

Call around, but book time is probably 2-3 hours. You could do it yourself, there’s not a lot to it.


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I did that MPFI upgrade myself, but it's not a simple job.
If you do decide to tackle it, for God's sakes take a crapload of pictures every step of the way so you can put it all back together. And label the various hoses and wires with tape or something. Pay particular attention to where each nut and bolt came from.

I did this job once, not sure I'd do it again. YMMV.

Tachyon said:

I did that MPFI upgrade myself, but it's not a simple job.
If you do decide to tackle it, for God's sakes take a crapload of pictures every step of the way so you can put it all back together. And label the various hoses and wires with tape or something. Pay particular attention to where each nut and bolt came from.

I did this job once, not sure I'd do it again. YMMV.

Click to expand...

I'm still fingers crossed that the mechanic/installer can warranty the labor because I really don't want to do it myself. I don't know how it compares regarding PITA factor of doing injectors on a 454 Vortec but I have done many many of those because of bad luck and continually receiving bad ones

Ugh it's been a long few weeks. I finally had to just bit the bullet and install the injectors myself. I also replaced the cat and throttle position sensor that was spazzing out occasionally. Yay, no more stink and my eyes don't burn at stop lights. Unfortunately on my 2nd time driving it since the injectors getting replaced I had the engine stumble to like 300 rpms and back up to normal sitting at a light. I start going and it's kind of stumbling still and I notice the check engine light go on, not blinking, just steady. I also notice I am starting in 2nd gear and have no OD also which is interesting because it did this transmission thing before during my engine swap and it was because the 12v supply to the transmission shift solenoid was too weak so a relay was added to provide more power which solved my trans issues. Anyway, I'm stumped and defeated. This is the list of codes that came up which are all new, it was totally clear on first test drive and part way into the second. Thoughts?

I don't know anyone in my area to consult either. Anyone in Henderson/Las Vegas or know a good mechanic in that area?

The GM diagnostic tables for each code is available online at alldatadiy.com which is a subscription service. It’s about $30/year and, if you’re inclined, it would be worth looking into in order to knock out these codes. It’s pretty much an online copy of the factory shop manual, so all of the repair procedures are in there

Here is the one for P1860.












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Im not sure my input will be useful, but at any sign of weird electrical issues, i would double check all your grounds, battery connections, etc. And i have worked on a couple foreign vehicles that had the tps, and map sensors reveresed.(honda) not likely the issue, since most of the sensors are so far away is impossible to do. Could be a bad connection. I Use dielectric grease.