New Engine?

[mark4000]

My mechanic says I need a new engine. I have a misfire in cylinder 4 of my OHV 4.0 6 cyl.(Mazda B4000) along with the various system Rich/lean codes-1151,1152 bank2 and 0172. I have had issues with this lemon of a car from the time i bought it over twenty years ago (each year of the first 8 years or so always having to fix the car to clear the check engine lights before passing emission; $1000's and $1,000's of $'s; inevitably each year the check light would always come back. I would always just wait till the next year to deal with it.
Also, Around this same time in the mid 2000's and trying to get to the bottom of this continuing engine light problem, I had a compression check and one cylinder (I guess 4-I don't have the receipt) was low. It did run pretty well for over 10 years-maybe having to replace the spark plugs, wires etc, sensors, egr etc etc. every two years ( I eventually was doing them myself).
Now, about 8 months back the check engine light came on again. In Sept, hoping just replacing the top end gaskets (also chasing a valve cover leak) would solve the problem, but to no avail the check engine light came back.
I wanted this issue resolved, so in November I took it to a mechanic and they did a leak down test(negative), smoke test(negative) and a compression test which showed cylinder 4 at #100 and 6 at #140; others at 160 or above- I think. They said I need a new engine.
Although the car ran fine for the first 3 months and into the new year after the diagnosis (even took it out of town 100 miles a few times), eventually starting in late January or February, a few times the car would just stop in mid rev-Yikes! I would just restart it and go on-things were fine like this for a month or two, but now in the last month I have no power. I stay on small roads because I cant stay above 50 or 60 mph.
Before I take the plunge to just under $2,000 for a used engine replacement, I just trying to get opinions if this sounds like a bad engine and not just something me or the mechanic is misdiagnosing. Any wisdom or advice would be greatly appreciated.
Thanks, Mark

 

[Dirtman]

Well, you can't judge what the engine needs by compression alone. You need to find out why its low. 100psi is still a functional cylinder but barely so it's been like that for 20 years? Thats kinda concerning and impressive.

They need to do a wet dry compression test to determine if its a ring/cylinder issue or valve/head issue. I would say it could possibly be a head gasket issue, but there's no way a leaking head gasket would hold together with a slight leak over 2 decades.

 

[dvdswan]

So ask yourself,
How long do I plan on keeping this vehicle?
Do I want to keep putting money into this vehicle?
What is this vehicle worth to me?

You call it a "lemon of a car" but you keep putting money into it. Do you really enjoy the truck that much or do you just not want a monthly payment?

IMO, don't band-aid the truck. If needs an engine, buy a new engine. If you want to throw a used engine in it, save your money and buy a good used vehicle to save yourself headaches down the road.

 

[RonD]

I wouldn't do a new or used engine

I would replace the heads or do a valve job on them which ever is cheaper
4.0l heads like to crack so they need to be tested for that prior to doing a valve job so..........when you add up the costs some times new heads can be a better option

Loss of compression in one or two cylinders is head gasket or valves, rarely piston/ring issue those tend to lose compression equally and nearer the 450-500k miles point

The low end, crank/rod bearings and pistons and rings, tend to last above the 400k miles so not seeing the benefit of the full engine swap
If your miles are under 300k then I would just do the heads because of the low compression
Now AFTER the heads are off and mechanic see signs of ring wear(marks) in the lower compression cylinder walls THEN and only then would you consider a full engine swap

And the difference in cost should only be 3 hours max, because most of the disassembly has to be done to get an engine out, pulling the heads is just a little extra work


Can't speak to the earlier problems or codes, but there are more than a few DIYers and Pro Mechanics than will happily swap out parts because its easier than "thinking" about what might actually be causing the problem, lol, its just human nature

Having the exact current codes would be helpful
Codes are not written in english, well the kind of engish you would think
Lean doesn't mean engine is actually running Lean, same for Rich
These are computer codes referencing the OPEN TIME for the fuel injectors, at no time was engine running lean or rich
If an engine is actually running Lean it will ping/knock, and NO codes
If its running Rich then it will blow grey smoke, and again NO codes
So grain of salt when looking up codes

 

[mark4000]

Well, you can't judge what the engine needs by compression alone. You need to find out why its low. 100psi is still a functional cylinder but barely so it's been like that for 20 years? Thats kinda concerning and impressive.

They need to do a wet dry compression test to determine if its a ring/cylinder issue or valve/head issue. I would say it could possibly be a head gasket issue, but there's no way a leaking head gasket would hold together with a slight leak over 2 decades.

Dirtman: Thanks for the quick response. I don't know the results of the compression test 18 years ago or so-cant find the invoice.
Ok, the wet/dry sounds reasonable and that is why I don't know if I trust these guys (they are new to me but have a good rep). Why didn't they do a wet dry and why not suggest repairing the rings/cylinders, valves, head etc?... They just said replace new/used engine. They said head gasket was good but I have been loosing little coolant over time over the last few years, but very little. I would just top it off from time to time.
Really, for a $600 used engine from the bay delivered and 6 month warranty and installed in 8-12 hours(their estimate) around $2,000 is not a bad price. I bet a new head gasket would be minimum $1500.

 

[mark4000]

So ask yourself,
How long do I plan on keeping this vehicle?
Do I want to keep putting money into this vehicle?
What is this vehicle worth to me?

You call it a "lemon of a car" but you keep putting money into it. Do you really enjoy the truck that much or do you just not want a monthly payment?

IMO, don't band-aid the truck. If needs an engine, buy a new engine. If you want to throw a used engine in it, save your money and buy a good used vehicle to save yourself headaches down the road.

Dvdswan: Again, thanks for the quick response. I understand all those questions. I figure If i can get it fixed for $2,000 and it lasts another 5-10 years that would be fine (it still looks decent and I know all repairs that have been done to it over the years with a basically all new ac system). I only drive it around 3,000 miles a year and I have two other cars, so I like the idea of keeping a beater/older truck for my side landscape work I do here in Atlanta. My two other cars (Saabs) are 17 and 29 years old.
And I am looking at options for a newer used truck; money is not an issue since I just inherited a good amount, but I don't necessarily need or care for a nicer newer ride just putting around Atlanta once or twice a week. and who knows what you could get into buying a new used car. Buying any used car is always a gamble.
Also, I would just have to junk this car or sell for parts or just sell it to someone that will do the work himself, I guess.
Also, in two years I wont have to get emissions. It is a cheap ride even If I spend $2,000 now.

 

[mark4000]

I wouldn't do a new or used engine

I would replace the heads or do a valve job on them which ever is cheaper
4.0l heads like to crack so they need to be tested for that prior to doing a valve job so..........when you add up the costs some times new heads can be a better option

Loss of compression in one or two cylinders is head gasket or valves, rarely piston/ring issue those tend to lose compression equally and nearer the 450-500k miles point

The low end, crank/rod bearings and pistons and rings, tend to last above the 400k miles so not seeing the benefit of the full engine swap
If your miles are under 300k then I would just do the heads because of the low compression
Now AFTER the heads are off and mechanic see signs of ring wear(marks) in the lower compression cylinder walls THEN and only then would you consider a full engine swap

And the difference in cost should only be 3 hours max, because most of the disassembly has to be done to get an engine out, pulling the heads is just a little extra work


Can't speak to the earlier problems or codes, but there are more than a few DIYers and Pro Mechanics than will happily swap out parts because its easier than "thinking" about what might actually be causing the problem, lol, its just human nature

Having the exact current codes would be helpful
Codes are not written in english, well the kind of engish you would think
Lean doesn't mean engine is actually running Lean, same for Rich
These are computer codes referencing the OPEN TIME for the fuel injectors, at no time was engine running lean or rich
If an engine is actually running Lean it will ping/knock, and NO codes
If its running Rich then it will blow grey smoke, and again NO codes
So grain of salt when looking up codes

Ron: My B4000 has about 178,000 miles and no ping/knock, no grey smoke or very little. And like I told Dirtman above, the mechanic suggested a new engine but not give a repair option. Maybe they thought the repair would be almost as much as a new engine? Who knows. I will call them tomorrow and ask what you suggest to look at the heads and valves.
"Current codes" are different than codes? I only know the basics with my code reader.
They read:
0172-too rich
1151 lack of h0221Switch-Sensor indicates lean
1152 lack of h0221 Switch-Sensor indicates rich
and cylinder 4 misfire.
And like I said to DVDswan above, if i pay $,2000 (but yes $1,200 would be better) for a repair and it lasts 5-10 years that will be fine. It would be worth it to me to keep it up and running as a cheap, small size work truck that I use sparingly. I don't necessarily need anything nicer or newer.

 

[19Walt93]

An engine can run lean enough to set a code without pinging and rich enough to set a code without smoking. I'd be leery of tearing down a 178,000 mile engine if I wasn't going to completely go through it but I also wouldn't buy a 20 year old used engine unless I was going to rebuild it. If it passed the leakdown test that indicates the rings are sealing but at 178k they've got to be worn. It might be worth a second opinion but drive it for a while before bringing it in for diag and do not plug your code reader into it. We had an autozone 1/4 mile from the dealership and their $29 code readers caused us no end of problems.

 

[19Walt93]

A lemon by definition is a vehicle that can't be fixed. There is no such thing, everything can be fixed.

 

[Uncle Gump]

A lemon by definition is a vehicle that can't be fixed. There is no such thing, everything can be fixed.

You've never worked for Renault... or perhaps tried to repair a Fuego or a Lecar?

 

[RonD]

Walt the engine is never running Lean OR Rich, thats not what lean and rich codes mean

At 170k miles you should be on the 2nd set of Upstream O2 sensor, when were they last changed?


OK the codes
P0172 System too Rich (Bank 1)

P1151 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2
P1152 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Rich - Bank No. 2

P0304 Cylinder 4 Misfire Detected

Start with the misfire, bank 2 is Drivers side
And #4 cylinder is drivers side

How do O2 sensors work?
They detect Oxygen in exhaust using a chemical reaction, they can not see fuel, JUST OXYGEN
After 150k miles or 12 years they will run out of chemicals so can't be trusted, period
Same as having to replace the battery every 5 to 7 years, they just wear out

But lets say O2s are working
When a cylinder misfires that means NO OXYGEN was burned up, or fuel, and that oxygen is then dumped into the exhaust manifold on Bank 2(cyl 4 misfire)
O2 sensor on bank 2 sees that as "lean", too much oxygen in exhaust manifold on that bank
This is where computer comes in, it will set a Lean Code, it doesn't know why #4 misfired, so to be safe it opens up injectors on 4, 5, and 6(bank 2) longer to Richen the fuel mix
This reduces the Oxygen level in bank 2 exhaust manifold because 5 and 6 are now running a little richer, so less oxygen coming out of their exhaust ports

And now lets say #4 starts to work again, just because or maybe a new spark plug got it working again?????, doesn't matter
So #4 is working, BUT..............fuel trims on bank 2 are now too rich, so computer sets Rich code, and reduces the open time of the injectors
And thats how you end up with Lean and Rich codes on the same bank
If you were to read and clear codes as they came up you shouldn't get both lean and rich
But if you just drive with CEL on then you can

P0172 is the only oddity I see, I would just clear it and see if it comes back


If block looks good, i.e. pistons and rings then just changing the heads WOULD get you 10 more years assuming 12k miles a year, as far as the engine is concerned


If my ashtray is dirty I can either empty it or buy a new car with a clean ashtray
Either solves the problem
If I just empty the ashtray it cost less, but my radio could quit work a few days later
If I buy a new car ashtray is empty and less likely the radio would quit working
Yes, extreme example, lol, but its the same just a matter of degrees

The new engine should solve the problem, and new heads, IMO, should as well, it really just comes down to cost
And your mechanic may not want to warranty just a head replacement, he may feel more comfortable just replacing the whole engine
Its not his money, its yours, so empty the ashtray or buy a new car, lol, so he recommends buying a new car, he's is better off with that, not just for profit its also about reputation if he just does the heads and 12 months later there is a problem with low end, he's the jerk that didn't replace the whole engine

 

[mark4000]

Walt the engine is never running Lean OR Rich, thats not what lean and rich codes mean

At 170k miles you should be on the 2nd set of Upstream O2 sensor, when were they last changed?


OK the codes
P0172 System too Rich (Bank 1)

P1151 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2
P1152 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Rich - Bank No. 2

P0304 Cylinder 4 Misfire Detected

Start with the misfire, bank 2 is Drivers side
And #4 cylinder is drivers side

How do O2 sensors work?
They detect Oxygen in exhaust using a chemical reaction, they can not see fuel, JUST OXYGEN
After 150k miles or 12 years they will run out of chemicals so can't be trusted, period
Same as having to replace the battery every 5 to 7 years, they just wear out

But lets say O2s are working
When a cylinder misfires that means NO OXYGEN was burned up, or fuel, and that oxygen is then dumped into the exhaust manifold on Bank 2(cyl 4 misfire)
O2 sensor on bank 2 sees that as "lean", too much oxygen in exhaust manifold on that bank
This is where computer comes in, it will set a Lean Code, it doesn't know why #4 misfired, so to be safe it opens up injectors on 4, 5, and 6(bank 2) longer to Richen the fuel mix
This reduces the Oxygen level in bank 2 exhaust manifold because 5 and 6 are now running a little richer, so less oxygen coming out of their exhaust ports

And now lets say #4 starts to work again, just because or maybe a new spark plug got it working again?????, doesn't matter
So #4 is working, BUT..............fuel trims on bank 2 are now too rich, so computer sets Rich code, and reduces the open time of the injectors
And thats how you end up with Lean and Rich codes on the same bank
If you were to read and clear codes as they came up you shouldn't get both lean and rich
But if you just drive with CEL on then you can

P0172 is the only oddity I see, I would just clear it and see if it comes back


If block looks good, i.e. pistons and rings then just changing the heads WOULD get you 10 more years assuming 12k miles a year, as far as the engine is concerned


If my ashtray is dirty I can either empty it or buy a new car with a clean ashtray
Either solves the problem
If I just empty the ashtray it cost less, but my radio could quit work a few days later
If I buy a new car ashtray is empty and less likely the radio would quit working
Yes, extreme example, lol, but its the same just a matter of degrees

The new engine should solve the problem, and new heads, IMO, should as well, it really just comes down to cost
And your mechanic may not want to warranty just a head replacement, he may feel more comfortable just replacing the whole engine
Its not his money, its yours, so empty the ashtray or buy a new car, lol, so he recommends buying a new car, he's is better off with that, not just for profit its also about reputation if he just does the heads and 12 months later there is a problem with low end, he's the jerk that didn't replace the whole engine

Thanks for the info. Always good to learn.
I will reset it again and have many times already. I cant remember it these codes are the exact same as other times.
Hah, and who knows how many o2 sensors have been replaced. I think i have done most of them at least twice in the last 12-15 years or so over maybe 70,000 miles and in those first 8 years of ownership, I would say mechanics replaced them at least two times along with replacing the spark plugs and wires 2 or 3 times.

You might be right on the mechanic not wanting to warranty a head job. I spent $500 with them just for those tests and a Mass Air Flow wire pigtail fix was included which I don't know if that helped any with the codes. Maybe one. I think they said it had 6 codes when the ran the diagnostic. So second opinion could be an option but now just more money. I will talk with them tomorrow.

 

[19Walt93]

Rich or lean codes can absolutely mean the engine is running rich or lean but the codes are not a diagnosis, they're a symptom and the first step down the diag path. We had countless customers come to us after replacing O2 sensors because their mickey mouse tester wasn't set up to display codes and it said "O2 sensor fault"- either rich or lean. If a tech is willing to put new heads on a 170,000 mile short block without giving you a long explanation of what might happen he's not your friend. If he's willing to guarantee something like that I'd question hos honesty.

 

[RonD]

No, the codes mean the computer has opened or closed the injectors +/-15% more or less than it calculated to get O2 sensors to read correct oxygen levels
So assuming O2 sensors are working then at no time was engine actually running Lean or Rich

 

[wildbill23c]

So ask yourself,
How long do I plan on keeping this vehicle?
Do I want to keep putting money into this vehicle?
What is this vehicle worth to me?

You call it a "lemon of a car" but you keep putting money into it. Do you really enjoy the truck that much or do you just not want a monthly payment?

IMO, don't band-aid the truck. If needs an engine, buy a new engine. If you want to throw a used engine in it, save your money and buy a good used vehicle to save yourself headaches down the road.

This is the huge thing. How long do you plan on keeping it. If its just a bandaid to get through till you find a replacement vehicle, its not worth replacing or rebuilding an engine. My engine replacement in my 88 Bronco 2 cost me $6,000, most of which was labor and replacement parts or wear parts that the engine rebuilder's warranty don't cover if they fail type nonsense. I also had the transmission rebuilt which was over $2k. Yes I plan on keeping my Bronco 2 as long as I can, I enjoy driving it, its a small vehicle that works great for back roads and trails, it still cost less than one of those side by side things that don't have a cab, AC, or heat....my Bronco 2 has all that LOL. It'll run up and down the roads and trails just like all those $20K+ UTVs and ATVs, but I have a cab with heat and AC most of those UTV's don't at least not for $20k, and even at $20k I'd rather buy a nice clean almost new pickup for that kind of money.

Also, take into consideration a 20-30 year old truck is maybe worth $1-2k in good condition. A bad engine and/or transmission makes it worth less, like scrap price of maybe a couple hundred bucks....so, if you really, really, really love that truck maybe an engine rebuild or replacement makes sense, but what kind of condition is the body in, frame, axles, etc. too, no sense replacing or rebuilding the engine in a truck that the frame is rotted out, body panels falling off and rotted out, etc.