Category Archives: Engines

Oil Pan Pump Replacement on a 351W

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As many of us FSB owners know the oil pan has a tendency to rust out, and what a wonderful thing because of how much work it takes to change. It took me seven hours of lying on my back in the drive way, getting dirtier than I ever have been before. This is a walk through of with I did.

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GM 2 Digit codes for 82 and up (non OBD-II)

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code code definition
12 diagnostic mode
13 02 sensor or circuit
14 coolant sensor or circuit/ high temp indicated
15 coolant sensor or circuit/ low temp indicated
16 system voltage out of range
19 crankshaft position sensor or circuit
21 throttle position sensor or circuit- voltage high
22 throttle position sensor or circuit- voltage low
23 mixture control (m/c) solenoid or circuit (carbureted models)
23 manifold air temperature (mat) sensor or circuit (1990 and earlier models) 23- intake air temperature (iat) sensor circuit (fuel-injected models)
24 vehicle speed sensor (vss) or circuit
25 manifold air temperature (mat) sensor or circuit – high temperature indicated (1990 and earlier models)
25 intake air temperature (iat) sensor or circuit – high temperature indicated (1991 and later models)
26 quad driver module circuit
27 quad driver module circuit
28 quad driver module circuit
29 quad driver module circuit
31 park/neutral position (pnp) switch circuit
32 baro sensor or circuit (carbureted models)
32 egr circuit (fuel-injected models)
33 manifold absolute pressure (map sensor signal voltage high
33 mass air flow (maf) sensor or circuit – excessive airflow indicated
34 manifold absolute pressure (map) sensor signal voltage low
34 mass air flow (maf) sensor signal – low airflow indicated
35 idle speed control (isc) switch or circuit (shorted) (carbureted models)
35 idle air control (iac) valve/ circuit
38 brake switch circuit
39 torque converter clutch (tcc) circuit
41 no distributor signals to ecm, or faulty ignition module ( carbed models)
41 cylinders select error- mem-cal or ecm problem ( fuel-injected models
41 cam sensor circuit (3.8 engine)
42 bypass or electronic spark timing (est) circuit
43 low voltage at ecm terminal l (carbureted models)
43 knock sensor circuit
44 oxygen sensor or circuit – lean exhaust detected
45 oxygen sensor or circuit – rich exhaust detected
46 power steering pressure switch circuit
48 misfire diagnosis
51 prom, mem-cal or ecm problem
52 calpak or ecm problem
53 egr fault (carbureted models only)
53 system over-voltage (ecm over 17.7 volts)
54 mixture control (m/c) solenoid or circuit (carbureted models)
54 fuel pump circuit (1986 and later models)
55 oxygen sensor circuit or ecm
55 fuel lean monitor (2.2l engine)
61 oxygen sensor signal faulty (possible contaminated sensor)
62 transaxle gear switch signal circuits
63 manifold absolute pressure (map) sensor voltage high (low vacuum detected)
64 manifold absolute pressure (map) sensor voltage low (high vacuum detected)
66 pressure sensor or circuit air conditioning

Holley Truck Avenger tips for Off Roading

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I’ve wanted to write a definitive Holley Truck Avenger thread, and I’m finally getting it done. I’m going to cover some tuning tips that I have applied with great success and also a review of my trail experiences on how well the carburetor operates.

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I see a lot of posts asking about whether the Truck Avenger works and what to do about the off-idle stumble/hesitation. Hopefully this thread will come up on some searches, and if not at least I can just link it and save myself more typing. :deal:

I had some bad luck with a couple of qjets, so I ended up buying a used Truck Avenger (TA) from a member here. It seems as though the TA is the last attempt to put off an FI swap. So this means you can find a lot of TAs for sale here, ebay, and Pirate with only 1-year’s use and low mileage. Don’t pay more than $250, because you should be able to find one for that price.

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Now here’s the first kernel of wisdom. Make sure to verify the list number on the airhorn. It needs to be 90670-2. See Figure 1 to find the list number. The serial is the key. If it is a old or no dash number, run away. Those versions had some sort of factory flaw that causes the infamous off-idle stumble and you’ll never get rid of it.

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The good news is that even if you already have a old or older version, all is not lost. Holley has been very good about replacing these older versions with the newest serial version. There are some observable differences between the carburetors, so I do believe there are some fundamental design changes.

You need to contact Holley and explain your problems, and they will swap out carburetors for the cost of you shipping them your carburetor. That is based on all the cases I’ve heard of from others.

When I swapped mine I didn’t need any type of proof of purchase, but I have heard from others lately that they are asking for a copy of the sales receipt, so beware. It was a great deal for me because I got a new carb for $250+shipping twice.

Now I know that Holley advertises all over the place the TA is a bolt and go carburetor. It has not been my experience that this is indeed true. I’ve only read a few instances where this is the case, and I don’t think any of these people were installing the carburetor on full size Chevy trucks with 350s.

All of the information I’m about to share is based on my experiences installing a 670cfm Truck Avenger on a rebuilt 350 with a mild cam in a full-body K5. Your results may vary some, but I think it will still provide a good basis for most CK5 trucks.

My primary source of information has been a website called There is a lot of information about GM engines related to tuning, carburetors, and fuel injection. I’ve never posted on the forum because I’ve found the answers to all my questions through searching. I will try to link some pertinent threads throughout this post.

It seems that there are some common tuning measures for Holley carburetors on 350s. Basically they seem to work best with a .035 accelerator pump discharge nozzle and Blue accelerator pump cam in the #2 hole. I’ll give a little detail on each of these items.

Refer to Figure 2 for what the accelerator pump discharge nozzles look like. They are sometimes referred to as squirters.

Figure 3 shows how the nozzles are installed/removed. It’s pretty self-explanatory; the only trick is to not loose the bottom washer. It’s not a huge issue as long as the primary butterflies are closed but just don’t let the washer fall own into the manifold. If it does, you gotta fish it out. I’ve had success using Vasoline to hold it on. The nozzles just barely fit between the choke butterflies and the airhorn. I use my pinkies to lift it in and out.

You can tune the nozzles by watching the exhaust. Increase size until you get black smoke out the exhaust when you punch the throttle. Then drop down one size. My exhaust is too short to see the discharge smoke, so I just went with the .035 nozzle and left it alone.

The next trick is to replace the accelerator pump cam. They are available in a kit, part number 20-12 pictured below.

The accelerator pump cams are sized by color lightest to heaviest shot as follows: White, Blue, Red, Orange, Black, Green, Pink and Brown. The other thing to take into account is the profile of the cam. From the research I’ve done, it seems that 350s like a heavy initial shot from the accelerator pump.

The searching I did on recommended a blue cam in the #2 hole. That is what I did, and it works just fine.

In the picture below, note where the arrow is pointing and you will see there is a counter-sunk screw head. In the picture the screw is in the #1 hole. Below this hole you can see another open hole, it is the #2 hole.

On the blue pump cam and most of the other pump cams there are two holes and they correspond to the holes on the throttle lever. Top hole is #1 and the bottom hole is #2. So to install the blue cam in the #2 hole you put the screw through the bottom hole on both the throttle lever and pump cam.

After doing this you need to verify that the override spring is adjusted properly. Make sure that the pump lever to pump cam clearance is set correctly. Some people misinterpret the .015″ clearance figure specified by Holley. There must be a minimum of .015″ extra travel at WOT available to the pump diaphragm.

At idle there should be Zero clearance between the pump cam and the pump accelerator linkage arm. Any free play at this point can cause a hesitation even with the correct cam and shooter installed. I always add 1\2 to 1 turn preload to the pump spring after adjusting to zero clearance. Seems to help sharpen the pump shot. Pump shot should be immediate and sharp with the slightest movement of the throttle. Dribbling is an indication of a problem.

The only other adjustment I made was jetting down for altitude. Holley recommends 1 size for every 2,000ft change in elevation.

I have found that the idle setting can play a role in the off-idle hesitation. I was running my idle kinda high, about 700RPM in drive, after changing the pump cam. I still had a hesitation. I’ve dropped the idle down to 550RPM, and that was the final adjustment needed to eliminated and hesitation. I believe this is because the lower idle allows the pump cam to ramp up more to get that big initial shot.

Don’t think that what I’ve post above is guaranteed to work your truck, it is just what I’ve found to work for me. Hopefully at the very least it will give you a good starting point.

These are some helpful threads from, which is basically where I found most of the stuff that I did. Pay special attention to posts by Chickenman35; he knows his stuff.…ht=BLUE+holley…ht=BLUE+holley…ht=BLUE+holley…ht=BLUE+holley…ht=BLUE+holley

So how does the Truck Avenger perform on the trail? It’s worked great for me so far. I’ve only had it stall once and it started right back up. The following obstacle is where the carb stalled:

I’ve done other obstacles with no issues:

Winter of 2006, I flopped the truck on its side into a creek bed. It was actually still sputtering a little sitting on its side. I don’t think it would have actually ran long, but I did have to shut the key off. Once we got the truck on all fours sitting on that bank, I was able to reach in and it started right up. I drove the truck up the bank with assist from a winch.

I’m not claiming the Truck Avenger is better or even as good as fuel injection. But for those not ready to make that leap, I feel the Truck Avenger is an excellent option. For me personally, it is much easier to tune than a quadrajet.

Hope this helps some of you fellow wheelers.

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Replacing the rear main seal in a 350 small block Chevy

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Discuss this article with the author and other forum members here.
The idea of replacing my rear main seal was very uncomfortable for me. Something about the idea of pulling main bearing caps had me feeling very skittish. However I guess my hatred of oil leaks evoked stronger feelings than my nervousness about replacing the rear main seal.

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Replacing the rear main seal in a 350 small block Chevy Image 1

First off if you post up on any GM board about an oil leak that presents as oil running down the back of the block and over the starter, most people will tell you it’s a leaking valve cover gasket, intake manifold gasket or oil pressure sender. These are very common and should definitely be checked first. Believe me; given my feelings about changing the rear main seal, I had hoped like hell this was my problem. No matter how many times I checked or how hard I wished, it just wasn’t the case.

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Just to be sure, I had taken my truck to the mechanic for some exhaust work and I asked him to take a look at it. His first response was that it was probably coming from the valve cover gasket. They checked it out and it wasn’t the valve cover gasket or any of the other usual suspects. They believed it was the oil pan gasket and rear main seal. So I knew I had to knuckle down and just do it.

While I’m no treehugger, I do like to do my part to keep the environment clean. Shoring up any fluid leaks in your truck is a good way to do this.

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Based on the recommendation of the mechanic, I purchased a one-piece rubber oil pan gasket made by Fel-Pro, part number FEL-OS34509T. I was definitely worth the extra money for doing this job with the engine in the truck. I purchased the most expensive rear main seal I could find on Summit Racing in hopes that I was getting what I paid for; it was also made by Fel-Pro part number FPP-2912 and it’s made with a material called fluoroelastomer.

An alternative would be the Peterson Fluid Systems SM86625 Rear Main Seal for Small Block Chevrolet 350
Those of you like me that wondered what fluoroelastomer is, here you go:

  • Fluoroelastomers are a class of synthetic rubber which provide extraordinary levels of resistance to chemicals, oil and heat, while providing useful service life above 200°C. The outstanding heat stability and excellent oil resistance of these materials are due to the high ratio of fluorine to hydrogen, the strength of the carbon-fluorine bond, and the absence of unsaturation. Fluoroelastomers are referred to generically as FKM polymers per the nomenclature noted in ASTM D1418. In the SAE J200 / ASTM D2000 classification system for rubber materials, fluoroelastomers are documented as a HK material, and can be found in the HK section of this specification.

The procedure for the rear main seal replacement is pretty straight forward. As long as you are careful and take your time, it shouldn’t be a problem. I can comfortably say that now that I’ve done it.

First step is to drain your oil. I can’t imagine the mess you’d have if you didn’t!
Most procedures I read have you remove the starter, I didn’t. I thought I might regret it, but it was never an issue for me.

Next step would be to remove the oil filter.

Then take off the dust cover. Now you can remove all 18 bolts holding the oil pan on. There are four 5/16″ bolts and the rest are ¼” bolts. My one-piece gasket kit included new bolts so I just threw the old ones away.

Lucky for me, my engine was rebuilt a few years ago so just a little prying with a screw driver was necessary to get the pan to break loose. With the pan removed, this is what you’ll see:

Replacing the rear main seal in a 350 small block Chevy Image 2

The next thing I did was removed the oil pump. There is just one bolt holding it in place and it uses a 5/8″ socket. The drive shaft that connects the oil pump and distributor will come out with it.

Next step is to remove the main bearing cap. On my motor there were only two bolts to removed, also require the 5/8″ socket. Tap the cap gently a couple of times and it’ll come loose. You can see it below with the blue rear main seal, this would be the bottom half of the seal.

Replacing the rear main seal in a 350 small block Chevy Image 1

Be careful not to damage the bearing material you can see here at the bottom. A bad gouge or scratch and you’ll get an oil leak that’ll never end.

The bottom half of the rear main seal simply pops out of the main bearing cap. The top half that’s still in the motor requires a bit more effort. I used a blunt ended punch and a hammer to tap one end of the seal. It didn’t take much to move the seal around enough to where I could get a hold of the other end with a pair of needle nose pliers. Just pull it the rest of the way out.

At this point I went ahead a removed all of the old gasket material from the engine and the oil pan. It came of surprisingly easy. One nice thing about doing this in the truck is gravity helps to keep any debris out of the motor.

Now it is time to start putting things back together starting with the new rear main seal. This is what my new seal looked like:

Replacing the rear main seal in a 350 small block Chevy Image 4

There are the two seal halves and the plastic shoehorn we’ll discuss later.
The first thing I was uncertain about was in regards to the “seal lip.” I was pretty certain I knew what they were referring to, but as you’ll recall I felt skittish about this whole thing so I wanted to be certain I had it right. You must be certain to install the seal with the seal lip facing the front of the engine, so it is very important to get it right. I have an arrow below indicating the seal lip on my new seal:

Replacing the rear main seal in a 350 small block Chevy Image 5

In the picture below you can also see the seal lip and how it rides on the crank. The oil pressure actually helps to further seat the lip against the crank.

Replacing the rear main seal in a 350 small block Chevy Image 6

Starting with the upper half, liberally coat the seal with fresh engine oil but keep the ends free of oil. This is so they will seal better once butted together. Now is when the plastic shoehorn comes into play, the little fella pictured below:

Replacing the rear main seal in a 350 small block Chevy Image 7

You will insert this into the upper seal channel so that the little tab will ride in the seal’s groove. It keeps the seal from getting nicked up by the edge of the block. Here’s a good picture from someone else’s install:

Replacing the rear main seal in a 350 small block Chevy Image 8

I thought it was going to be difficult to push the seal in, but it wasn’t that bad at all. Here’s where the directions included with my seal part from the typical directions. They recommend offsetting the seal 3/8″ from flush with the block. In other words, one side will be sticking 3/8″ out of the block and the other side will be 3/8″ inside the block. Fel-Pro states that not doing this is one cause for leaks after install.

Now install the bottom seal half in the bearing cap. Again liberally apply fresh engine oil keeping the ends dry. Also be sure to offset the seal 3/8″ to match the upper half in the motor.

Next apply some RTV sealer to the bearing cap where it mates with the engine block. As illustrated here:

Replacing the rear main seal in a 350 small block Chevy Image 9

Again this is another potential source for leaks.

Now install the main bearing cap back into the block. I thought it was going to be difficult to get the portion of the lower half that was sticking 3/8″ above the cap into the seal channel, but it wasn’t. Once you have the cap pressed into place, bolt it in. These bolts torque to 65ft-lbs on my motor.

The oil pump goes in next. Guide the driveshaft up into the hole to engage the distributor. You may need to rotate it some to get it to fully engage. You’ll know if it isn’t because the pump mounting flange won’t fully seat against the main bearing cap. Torque this bolt to 65ft-lbs.

Now it’s time to install the oil pan. I like to wipe down all of the mating surfaces with lacquer thinner, but not the gasket. Also make sure the flange on the pan is flat; you’ll usually find it is dimpled where the bolt holes are. I used a block of wood and a hammer to flatten the dimples out.

The instructions for the one piece gasket specifically say not to use gasket sealer, except in 2 places;

  1. Where timing chain cover meets the block
  2. Where rear main bearing cap meets the block

The one piece gasket set makes installing the pan a breeze. The kit comes with what they call snap-ins, little plastic dowels pictured below.

Replacing the rear main seal in a 350 small block Chevy Image 10

One end threads into each of the 4 large corner bolts. There’s a slot for a flat blade screw driver that makes it a breeze to thread in. Then you pop the gasket on over the snap-ins by the oil pan. You can see the flared parts of the snap-ins that hold the gasket and pan up. Now start the other 14 smaller 1/4″ bolts with the star washers. Once the bolts are snug you can remove the snap-ins and thread in the last four 5/16″ bolts with star washers. Again the Fel-Pro gasket kit included all new bolts.

Torque the bolts to no more than 100in-lbs. I went around the pan 3 times before they were all consistent. The gasket also has sleeves around the bolt holes to prevent over torquing.

Install the inspection cover.

Install oil filter. I like to add as much oil as I can to the filter before installing.
Refill the oil pan and you’re done.

Hopefully you will hit the road leak free!

Reader’s Tips

Tim Says:

Oil pan gasket surface should be cleaned while main cap and oil pump are installed (either  before removal of components or after installation of new parts) as this will help to keep debris off bearing and journal surfaces.  Also fill up oil filters by outer holes only, DO NOT pour oil in the center hole.  Oil flows in the small holes and out center hole, any dirt in center hole will go directly to bearing surfaces and, depending on hardness of bearing will either destroy bearing or imbed itself in the bearing’s surface.


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