idiot light

[Hobbs]

In my 1988 sub, 7.4 L, my idiot light “service engine soon” has been coming on. It really has not been predictable. Does not come on every trip. Usually only comes on at the beginning of the trip, and does not stay on for more than 5 min or so.

I know this light could mean a multitude of problems that are easily diagnosed by the dealer with the computer. My question is, are there any cheap/most common causes of this on and off “service engine soon” light that I could check or change before submitting to the dealer?

For what it is worth…I changed spark plugs the other day and they were clean and dry. The engine does run a little rough. Probable needs a timing adj.

Hobbs

[Bob Gervais]

Originally Posted by Hobbs

In my 1988 sub, 7.4 L, my idiot light “service engine soon” has been coming on. It really has not been predictable. Does not come on every trip. Usually only comes on at the beginning of the trip, and does not stay on for more than 5 min or so.

I know this light could mean a multitude of problems that are easily diagnosed by the dealer with the computer. My question is, are there any cheap/most common causes of this on and off “service engine soon” light that I could check or change before submitting to the dealer?

For what it is worth…I changed spark plugs the other day and they were clean and dry. The engine does run a little rough. Probable needs a timing adj.

Hobbs

http://www.roberthancock.com/efi/

Here's a very informative page on reading codes, and finding out what they mean. It's really simple on the pre-96 trucks to read and interpret the codes, and there's many people here that can help you.

Don't waste your money on a code reader, all it is is a jumper wire encased in a large plastic box. Don't waste your money at the dealer either. Many dealers get $80 or more just to do the "diagnostics", which is nothing more than reading the codes, and should take no longer than ten minutes.

Let us know if you need any help!

[Hobbs]

Bob thank a bunch. That web site was great and probable saved me a lot of money.

Results: code 44 which in my Chiltons says o2 sensor measuring lean.
Action: Change the o2 sensor, change the fuel filter (engine actually running lean due to clog. This car sat with a full tank for 5 years.)

Any other suggestions for fixing the code 44?

Thanks again.

Hobbs

[Bob Gervais]

Originally Posted by Hobbs

Bob thank a bunch. That web site was great and probable saved me a lot of money.

Results: code 44 which in my Chiltons says o2 sensor measuring lean.
Action: Change the o2 sensor, change the fuel filter (engine actually running lean due to clog. This car sat with a full tank for 5 years.)

Any other suggestions for fixing the code 44?

Thanks again.

Hobbs

No problem at all sir, glad to help!

The important thing to remember when reading codes is that one may set of another, especially in the case of O2 sensor codes.

But, in this case, since you only have the code for the O2, I'd say it's a safe bet that the O2 is shot. Especially since the truck sat for so long.

Changing the fuel filter is a good idea. Maintenance never hurts.

The only other thing I could think of that would cause an O2 to read lean, but not spit out any other codes, is a vacuum leak. Spray some carb cleaner around the throttle body base, intake manifold, and vacuum lines. If there's any change in idle speed/quality when spraying around a particular area, you have a vacuum leak there, that will need to be repaired. Once it's repaired, disconnect the battery for five minutes or so to clear the computer's memory (and stored check engine light codes), and drive it for a while to see if the problem still persists.

On the subject of sensors, I've found that many of the aftermarket ones work fine for other areas (TPS, MAP sensor, etc), but I've had crappy luck with aftermarket O2's. I would suggest getting an AC Delco sensor, if you end up needing one.

[Hobbs]

Will let you know. Many thanks, again!


Hobbs

[Captkaos]

You may also want to check for exhaust leaks for a code 44. Especially if it started doing it when it got cold.

[Hobbs]

Captkaos,
you may be right on. My muffler is loose and yesterday I was underneath with the engine running. (1/2 way at least not brave enough to be on the ground, fully under a hot running car) and at the point where the right exhaust turns to join the left I could see a heat vapor coming from a very defined spot. Could not see the hole, but probable saw the signs of exhaust leak.

Thanks for your help.


Hobbs

[screwballl]

i would say fix exhaust, if possible get dual exhaust if you plan on keeping it for some time....
replace O2 and fuel filter.. oh wait that stuff was already mentioned here...

also if you havent already done it, might as well drain the gas tank and put some fresh stuff in there.... old gas can and will be the cause of many many problems in the future...

[Hobbs]

Let me ask what may be a stupid question. By converting a car with a cat. converter to dual exhaust would you just run 2 cat. converters? My experience has been with all pre cat. converters back when I was young so never thought about a modern true dual exahaust. I kind of excepted that the cat. converter did away with the benifits of a dual exhaust.

Interesting idea though, I was going to add a cat back flowmaster anyway but would love a true dual exhaust system. (let that thing really breath)

Hobbs

[Bob Gervais]

Originally Posted by Hobbs

Let me ask what may be a stupid question. By converting a car with a cat. converter to dual exhaust would you just run 2 cat. converters? My experience has been with all pre cat. converters back when I was young so never thought about a modern true dual exahaust. I kind of excepted that the cat. converter did away with the benifits of a dual exhaust.

Interesting idea though, I was going to add a cat back flowmaster anyway but would love a true dual exhaust system. (let that thing really breath)

Hobbs

That's a tough one, legally. Laws vary state to state, so you'll have to ask an exhaust shop in your area about it. Many shops around here (RI) are very hesitant to modify anything before the cat, or the cat itself, due to our emissions laws. My state does emissions testing every two years, until the vehicle is 25 years old. The guy I go to doesn't really care what's on or off the truck, as long as it passes the sniffer test.

That said, here's what I just completed doing on my 87. I had the emissions done last year, which means it's good until '07. About three months after that, the original converter popped out the little plug on the bottom, causing a major leak. I didn't have the money to do much about it at the time, so I bought a section of 3" diameter pipe at the parts store, cut out the cat, and welded the straight pipe in place. Right after that, the y-pipe started rotting at the flange that attaches to the manifold. I priced out a whole stock replacement exhaust with a converter and a Flowmaster 50 series muffler, and it came in right about $350-$400. That was with me doing the work (which I always do anyway).

I then searched around for dual exhaust options, and found a Flowtech pipe system on Ebay for $99 shipped. True duals, no converters, no mufflers, but it had all the mandrel bent pipes, clamps, and hangers I needed. I bought a set of Flowtech Raptor mufflers to go with it, and installed the whole thing. Sounded OK, but a little unbalanced as a true dual system. So, I bought an h-pipe setup from Summit Racing, and added that in before the mufflers. It balanced out the sound, added some low end grunt, and I'm happy with the sound and quality of the system.

I still have no converters, but I have plenty of space to add them in right near the manifolds where they belong. My plans are, later this year, to buy a couple of high flow converters (they're on Ebay all the time for $40 or so), and a couple of Flowmaster 40 series mufflers, which are also on Ebay all the time fairly cheap (with the converters and h-pipe, the current muffs won't have the sound I want), and add that to the system. I'll then be emissions compliant, have a true dual exhaust with an h-pipe, and a kickass sound.

I've seen systems for the big blocks on www.summitracing.com, www.jegs.com probably has them too. Same as mine, they're 2 1/4" pipes, all hardware, but no mufflers. I think they're about $125 or so. If you want true duals, and can do it yourself, this is really the way to go. Add some converters and Flowmasters to it (if I had to do it again, I'd have waited until I had the money to buy everything), and the h-pipe from Summit, and you've got yourself a nice system for around $350.

[Hobbs]

Man, I got to do some research....

For starters, what I was planing on doing was adding this flowmaster cat. back system for $400.00 http://www.flowmastermufflers.com/pr...oducts_id=3710

But what you are telling me:
"I've seen systems for the big blocks on www.summitracing.com, www.jegs.com probably has them too. Same as mine, they're 2 1/4" pipes, all hardware, but no mufflers. I think they're about $125 or so. If you want true duals, and can do it yourself, this is really the way to go. Add some converters and Flowmasters to it (if I had to do it again, I'd have waited until I had the money to buy everything), and the h-pipe from Summit, and you've got yourself a nice system for around $350."

Is that with a little work, I could create a true dual with or with out a cat. for around $350.00.

1) Get the dual system from some place like summit
2)add a high flow cat. (side point, I am supprised about the ebay price, I quickly searched them the other day...around 240.00)
3) flowmaster muffler

Another question....Will changing these newer emission tuned engines to a dual exhaust with or without a cat. change the tuning of the engine? Will I create other problems by converting the exhaust system?

After some research, I may have more intelegent questions.

Hobbs

[Bob Gervais]

Originally Posted by Hobbs

Man, I got to do some research....

For starters, what I was planing on doing was adding this flowmaster cat. back system for $400.00 http://www.flowmastermufflers.com/pr...oducts_id=3710

But what you are telling me:
"I've seen systems for the big blocks on www.summitracing.com, www.jegs.com probably has them too. Same as mine, they're 2 1/4" pipes, all hardware, but no mufflers. I think they're about $125 or so. If you want true duals, and can do it yourself, this is really the way to go. Add some converters and Flowmasters to it (if I had to do it again, I'd have waited until I had the money to buy everything), and the h-pipe from Summit, and you've got yourself a nice system for around $350."

Is that with a little work, I could create a true dual with or with out a cat. for around $350.00.

1) Get the dual system from some place like summit
2)add a high flow cat. (side point, I am supprised about the ebay price, I quickly searched them the other day...around 240.00)
3) flowmaster muffler

Another question....Will changing these newer emission tuned engines to a dual exhaust with or without a cat. change the tuning of the engine? Will I create other problems by converting the exhaust system?

After some research, I may have more intelegent questions.

Hobbs

Doing the catback is fairly easy, probably a lot easier than doing true duals, all depends on how rusty your manifold studs are. My studs were rusty, and very thin. Knowing they would break, I saved myself some torture and just broke them off, and drilled them out. That was a pain, but the rest of the install was very easy. If you think you could handle having to drill out studs, go for it!

In my opinion, the dual 2 1/4 setup flows more than the stock system, based on the area of a single 3" pipe vs. the area of two 2 1/4 pipes. Is it necessary? Maybe not, but I did feel a difference in low end torque, and higher RPM power. Plus, I'm one of those types that would rather replace a worn stock item with a performance oriented aftermarket part. May as well upgrade!

The Flowmaster system is nice too, because all the pipes are mandrel bent, and you're getting a high flow muffler.

If it were me, I'd be going with the dual system, and a little more elbow grease to get it done. All depends on how much work you want to do.

As for the emissions tuning, you shouldn't have an issue at all. I'm guessing that you're worried that the increased exhaust flow might make mess up the fuel to air ratio? I know on carbed engines, it was a common practice to change jets, or idle mixture, after freeing up some airflow with an exhaust or intake (did this myself to many cars). On our Suburbans though, the O2 sensor and computer does have the ability to correct for airflow changes (as long as we're not installing a 6-71 blower! ).

So, you won't need any tuning, chips, or anything from adding either the true duals, or the Flowmaster system.

Hope this helps!

[Hobbs]

The fuel to air was exactly what I was worried about. Don't have the time these days to create unexpected projects. Glad to know that will not be a worry.

I hear you on the "amount of elbow grease" I am interested in expending. May just end up bolting the cat. back on and planning the true dual for another day. I am still going do a little research based on the ideas you have given me.

You have been a big help. Thanks Bob.

Hobbs.

[Bob Gervais]

No problem at all Hobbs, I'm glad to have been some help to you.

To be honest, there's an exhaust shop here in MA that will do a custom catback for $400. Flowmaster 50 series, single in, dual out, with two tailpipes and stainless tips, all welded. Toward the middle of the project of drilling out my studs, I reeeeealy started wishing I'd have gone that route.