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Hey Eric! How are *YOU*? I’m fine thanks 🙂
About the Jimmy (for a second I thought it was about a *Suzuki* Jimmy 😆 ) , I have a question.
Did you check the spark plugs? Maybe they are worn or incorrectly gapped, and the problem happens only when it is very very cold.
I keep thinking “if this was a carburettor engine I’d check the correct functionality of the starter/choke”, but in a fuel injection engine it should be the ECU that enriches the mixture when it senses the engine is cold.
So my other question is: seeing all that yuck inside the coolant, maybe that same yuck is on the coolant temperature sensor, and this fools somehow the ECU which in turn does not deliver the correct amount of fuel…However, to avoid speculation and stick with facts, your scanner did indeed tell the long term fuel trim for bank 2 was waaaay off.
So the ECU is detecting something and acting upon it, and this leads me to think the following: could it be the O2 sensor (or its heater?) for bank 2? (If there is one, I admit I don’t know a thing about GMC engines, for me they are like aliens, never seen one here in Italy 😆 )Hope this helps Eric!
Live long and prosper (and stay dirty!)
10nico
+5 LTFT does not seem like that drastic an amount. Over 10 I would be concerned, but alas I don’t know GM’s that well.. FWIW Some Toyotas have a tolerance of +- 20.
Here is my other question. If it was a vacuum leak caused by the spider injection system seal being bad on an intake manifold (glued), why was the LTFT only affecting one bank?
I get it that there was a vacuum leak causing an issue, but the LTFT being off on one side (and not both) is what puzzles me. It seems to me that it is not the LTFT causing the issue, but a vacuum leak and you just found the vacuum leak around the Fuel Injection Assembly…. The LTFT seems like a red herring….
Karl
When you look at short term and long term fuel trim it tells you a great deal about how the engine is running. In the case of the Jimmy, it was running lean on one bank and we found a vacuum leak to back that up. As for the spark plugs, I did check for an ignition misfire along with checking for vacuum leaks. I did not see anything to indicate a problem with the ignition system. If there was an ignition system problem it would likely show up under load, not at start up. If it had an ignition misfire that was bad enough to effect start up, I would think it would occur all the time. I saw nothing to indicate that the O2 sensors were having issues. The scanner showed they were switching just fine. If there was a heater failure there would have been a code for it. Besides, the O2 is not active at cold start up anyway. As for the coolant, I advised the customer that they would need to flush out the old coolant and possibly replace the intake gasket as well as the spider injection system. Yes, that ‘gunk’ would be on the coolant temp sensor but once again, I had known problems with vacuum leaks and coolant contamination. For me, that’s a good start. If there were other problems along the way I would have addressed them them.
I stand by my diagnosis and my assessment.
[quote=”ToyotaKarl” post=65027]+5 LTFT does not seem like that drastic an amount. Over 10 I would be concerned, but alas I don’t know GM’s that well.. FWIW Some Toyotas have a tolerance of +- 20.
Here is my other question. If it was a vacuum leak caused by the spider injection system seal being bad on an intake manifold (glued), why was the LTFT only affecting one bank?
I get it that there was a vacuum leak causing an issue, but the LTFT being off on one side (and not both) is what puzzles me. It seems to me that it is not the LTFT causing the issue, but a vacuum leak and you just found the vacuum leak around the Fuel Injection Assembly…. The LTFT seems like a red herring….
Karl[/quote]
It has to do with the design of the intake. It’s actually a collection of runners twisted together. You can have a vacuum leak that only effects one runner or side of the engine. If the vacuum leak is in a runner for that side of the engine, the the fuel trim readings will be off for that side. It just depends on where the leak is.
Not trying to get into an argument or call anyone names, but I didn’t think the intake manifold plenum on 4.3’s had runners. It is pretty much an open area… Hence why the FI lines can go to each cylinder. The runners are much further down in the manifold…. Any leak up around the opening for the fuel injector system should affect the whole system (hence both banks)… See other attachment below for the actual intake manifold…
Just Sayin…
Id say the vacuum leak is a good start.
Another wrench thrown in the loop could be something like: What if the rings are just worn? Lower compression when the engine is cold, causing a hard start. Verify with compression testing, or even leak down test.
Checking the fuel pressure when it’s cold versus when it’s hot would be a good place to look too. Older chevys like this are notorious for fuel delivery problems.
I think that the bad part too, was that you couldn’t duplicate the problem. That seems to happen a lot and, all you can really do is just what you did: address the known problems and tell them to bring it back when the problem is more frequent, or maybe just on a cold day.
[quote=”ToyotaKarl” post=65031]Not trying to get into an argument or call anyone names, but I didn’t think the intake manifold plenum on 4.3’s had runners. It is pretty much an open area… Hence why the FI lines can go to each cylinder. The runners are much further down in the manifold…. Any leak up around the opening for the fuel injector system should affect the whole system (hence both banks)… See other attachment below for the actual intake manifold…
Just Sayin…
[/quote]
I suppose it’s possible that there might be an issue with the injection system itself then. If fuel delivery was not even then you could have one bank that got more fuel than the other. Couple that with a lean condition cause by a vacuum leak and you could have one bank that doesn’t get enough fuel. In addition, it could have a leak where the intake meets the cylinder head. That would cause one bank to be lean and the other not.
My point is as I said in the video. If you have known problems, address those problems. Don’t go looking for more problems until you’ve fixed the ones you know about. Remember the rule of K.I.S.S.. We know we had a vacuum leak and crappy coolant. We also know that someone had been messing with the injection system and they could have screwed something up. It’s also well know that spider injection system is known for problems and GM intake gaskets are the worst on the market. Sometimes it’s best to start with the low hanging fruit and take it from there.
[quote=”study4ase” post=65037]Id say the vacuum leak is a good start.
Another wrench thrown in the loop could be something like: What if the rings are just worn? Lower compression when the engine is cold, causing a hard start. Verify with compression testing, or even leak down test.
Checking the fuel pressure when it’s cold versus when it’s hot would be a good place to look too. Older chevys like this are notorious for fuel delivery problems.
I think that the bad part too, was that you couldn’t duplicate the problem. That seems to happen a lot and, all you can really do is just what you did: address the known problems and tell them to bring it back when the problem is more frequent, or maybe just on a cold day.[/quote]
When I started out doing diagnostics, I tried to pick apart every single part of a problem. Over time I found that most issues have simple causes and therefore simple solutions. When doing diagnostics in particular, stick to the easy stuff. 9 times out of 10 the solution is right in front of your face. Don’t waste your time on the small percentage of problems that require more advanced diagnostics. Only go there if the situation warrants it.
Eric, I am in complete agreement about finding the known problems, and you did find a vacuum leak indeed.
So did you seal up the leak (what someone was probably trying to do before when they glued it together) and flush, fill and bleed the cooling system?
I don’t know if you noticed but when you shot the video there were definite differences in the readings of the O2 sensors. O2S21 did not look like it was moving in a full range (as compared to O2S11). Now, I know that both upstream will never match but they should be fluctuating between .1 and .9. O2S21 did not appear to go below .295, where O2S11 went to .135. This would cause me to check the O2 sensors. Perhaps a different type (brand) of sensor was being used, or Bank 2 O2 sensor is getting lazy…. I know that not using DENSO O2 sensors on Toyotas can cause issues as well as mixing brands of O2 sensors.
I know I only saw a couple of seconds of the O2S21, so maybe it did move full range… Suppose we could get into the chicken and egg discussion that the O2 is richer because the Bank 2 LTFT was increased! :woohoo:
As always, thanks for all you do.. and disagreement isn’t disrespect!!
Karl!
[quote=”study4ase” post=65037]Id say the vacuum leak is a good start.
Another wrench thrown in the loop could be something like: What if the rings are just worn? Lower compression when the engine is cold, causing a hard start. Verify with compression testing, or even leak down test.
Checking the fuel pressure when it’s cold versus when it’s hot would be a good place to look too. Older chevys like this are notorious for fuel delivery problems.
I think that the bad part too, was that you couldn’t duplicate the problem. That seems to happen a lot and, all you can really do is just what you did: address the known problems and tell them to bring it back when the problem is more frequent, or maybe just on a cold day.[/quote]
Hiya! 🙂
IMHO, after reading all replies I think these two hypoteses hold the better chance to explain the problem.
Also, this is the classical “ghost problem” , since it is not reproducible it cannot really be observed.
As an IT techician myself I hate these problems; all one can do is all Eric has done.And all that remains is the whole bunch of “what if”?
Well, for the sake of the Jimmy I really hope the owner did flush out and change the coolant and replaced the spider.
I would be curious to see the results of a compression test and of a leakdown test 😉
The thought comes to my mind to another GM truck (Chevy tahoe anyone? 😉 ) which had mechanical engine problems, especially cylinder compression problems.
By the way, to answer Eric, I have most definite experiences on older cars that had cold start problems which, in turn, could be resolved by tuning up the ignition system.
That’s way I pointed my finger to that possible problem.
Of course it’s experience that relates to old cars, which still had points and capactitor ignition, and they all seemed to show cold start problems that “magically” resolved by tuning up the ignition system.These were ignition systems made to work with almost no “safety margin”, and when they started to deteriorate the very first symptom was the cold start problem. (and maybe and increased fuel consumption)
I’m very sorry that the customer didn’t want to fix the problems, as this leaves all of us very very curious about the “possible what ifs” of this truck.
Let’s hope it hits Eric’s shop again 🙂
To all of you, my best
Live long and prosper (and stay dirty!)
10nico
[quote=”EricTheCarGuy” post=65028] If there was a heater failure there would have been a code for it. Besides, the O2 is not active at cold start up anyway. As for the coolant, I advised the customer that they would need to flush out the old coolant …[/quote]
Did the customer at least agree to the cooling system flush ? Seems odd that that maintenance item was skipped, especially when the rest of the engine compartment seemed reasonably clean !
Side question. New or repeat customer ? Do you think they will be back ?
I never heard of a “spider injector” so I did some research. The original looks like this
The current Delphi replacement part looks lie this
[quote=”wysetech” post=65139]WoW It’s been a while since i changed a “spider” It sure has evolved since the first one i saw.[/quote]
When the replacement part is so different it tells me that the engineers have said “Oh, well. That design did not work. Let’s go back to something more conventional !”[quote=”ToyotaKarl” post=65061]Eric, I am in complete agreement about finding the known problems, and you did find a vacuum leak indeed.
So did you seal up the leak (what someone was probably trying to do before when they glued it together) and flush, fill and bleed the cooling system?
I don’t know if you noticed but when you shot the video there were definite differences in the readings of the O2 sensors. O2S21 did not look like it was moving in a full range (as compared to O2S11). Now, I know that both upstream will never match but they should be fluctuating between .1 and .9. O2S21 did not appear to go below .295, where O2S11 went to .135. This would cause me to check the O2 sensors. Perhaps a different type (brand) of sensor was being used, or Bank 2 O2 sensor is getting lazy…. I know that not using DENSO O2 sensors on Toyotas can cause issues as well as mixing brands of O2 sensors.
I know I only saw a couple of seconds of the O2S21, so maybe it did move full range… Suppose we could get into the chicken and egg discussion that the O2 is richer because the Bank 2 LTFT was increased! :woohoo:
As always, thanks for all you do.. and disagreement isn’t disrespect!!
Karl![/quote]
O2 sensors don’t operate at full range when idling. To get an O2 sensor to switch properly, you’d need to rev the engine up to 2k RPM. That’s how I tested my O2 sensors. And even with a lazy O2 sensor, that wouldn’t cause start troubles. The O2 sensors don’t come into play until the ECU goes into closed loop, which is when the engine is warm.
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