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Need urgent help (2004 EFI 8.1 Ltr Engine in Blazer 1981!!)

GMCbigblock

GMCbigblock

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CK-5ers,

Am seeking your help by sharing your valuable and proven-experience for my situation. Currently, I'm in process of fixing an 8.1 Ltr. (496 CID) engine donated from an Avalanche (2004 Year) into my 1981 Blazer; which currently has a tired 1996 5.7 Ltr (carburetor). My plan is to swap the current TH350 for a HD 5-Speed Manual Gear - which was donated from 2500HD GMC 4x4 truck (2005). The stock 1981 Transfer-Case (I think NP-204!!) is planned to remain and match with the new 5-speed manual gear. Your help is kindly requested for the following Q's:

1) The 8.1 engine is complete with all wiring, harness and the OBD (ECM). However, it's missing the 'Throttle Body'. I understand that a cable-driven unit is better to be used with the existing mechanical (cable-operated) acceleration-pedal. Should I buy a stock TB-Unit for the same model 2004, OR buy a TB of the earlier cable-operated model (2002) or get a TB of another after-market brand? If so which Make & Part #?
2) Should I maintain using the same stock wiring/harness/sensors or buy an after-market harness? Is so, which brand, web-site etc?
3) Has any one else done this projects before, and if so what are the other parts that I should secure to complete the job (we can customize the headers, and fix a large radiator of the 1997 7.4 Ltr in the place of the original one).
4) Any other valuable piece of info that can help.

I will highly appreciate hearing your earliest advice; which will help in the birth of another hard-core Blazer - thus enlarging the CK-5 Community.
THANKS for passing by, your reading-time and consideration to help!

Regards, AHMED
 
look up posts by a gent named Larry....pretty sure it's Larry. he put an 8.1 in his rig......he has an absolutely fantastic truck too. here's a pic, someone may remember a thread or something.

4578907101_ff41d56b25_b.jpg
 
Hi Shovelbill80, I tried searching for Larry but couldn't reach any result! I might be missing something! Is there any further clue or info that I can use? Thanks.
 
My search is still ongoing with no results, am heading no where!!. Any one can help in this distinctive forum. Thanks.
 
I am guessing here, so take this with a grain of salt:

1. I would recommend you use the same throttle body as came stock with the engine. The reason why is that the engine most likely has a Throttle Position Sensor (TPS) which the computer needs to manage the engine. If you do not have a TPS, the engine may not run well, or perhaps at all.

2. If the harness is 100% complete, it may be easier to use it and connect it into your existing system for power, ignition, etc. However, I have heard Painless wire harnesses are very good if you want to replace it. They make complete harnesses that should be easy to adapt.
 
Jessi, 496truck, you've been helpful and kind enough to spare some time to provide such valuable input. Appreciating this alot.
 
I'm doing this same swap in my Blazer (a '72) and have spoken with Larry at length.

1) The mechanical throttle body you want is on the Gen 6 454 engines - it will bolt right on - but you will likely need a throttle body spacer to make it fit. Here is one on Ebay - but you could probably find it cheaper:

http://cgi.ebay.com/ebaymotors/96-9...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

Note that these throttle bodies have the TPS in the side.

2) Wiring harness source:

http://www.jimsperformance.com/





Some misc links on 8.1:
http://67-72chevytrucks.com/vboard/showthread.php?t=400053
http://67-72chevytrucks.com/vboard/showthread.php?t=374432
http://67-72chevytrucks.com/vboard/showthread.php?t=373400


http://coloradok5.com/forums/showthread.php?t=266215&highlight=8100
http://www.hotrodlane.cc/81bbc/81bbc.html
http://coloradok5.com/forums/showthread.php?t=211721&highlight=transmission+engine+support

http://www.jimsperformance.com/links.html
http://www.pirate4x4.com/forum/showthread.php?t=598547&page=1
http://www.pirate4x4.com/forum/showthread.php?t=598547&page=9
http://pirate4x4.com/forum/showthread.php?t=631745
http://www.pirate4x4.com/forum/showthread.php?p=8452724&highlight=#post8452724

http://www.4wheeloffroad.com/brandpages/chevy/131_0205_project_excursion_killer_part_1/index.html
http://www.67-72chevytrucks.com/vboard/showthread.php?t=370820&highlight=8.1+4l80e
http://www.pirate4x4.com/forum/showthread.php?t=845109
http://www.pirate4x4.com/forum/showthread.php?t=457799
http://www.pirate4x4.com/forum/showthread.php?t=659156
http://www.pirate4x4.com/forum/showthread.php?t=667616





Here is some correspondence between Larry & I:

Mr. Dirty Larry:

Hello, my name is Ben - I live in Portland, OR. In the process of a frame off on a '72 K5. I've been reading your posts thoroughly over the past few weeks to learn as much as possible about 8.1s in older rigs.

I currently have an 8.1 in my '02 GMC Crew that I bought new. Love that engine - has 110K and still going strong.

I closed the deal on an '01 8.1 complete block today. Has wiring harness, CPU, accessories, pedal, alt, starter, etc, etc... This engine has supposedly:

A) 96K miles
B) was in '01 truck
C) was looked over by GM Master Tech who said it was a good running strong engine


I have two questions for you:

1) What should my first steps be after I get this engine? Can I simply drop it in and go? Or should I plan to do head gaskets, spark plugs, etc...

2) Do you have the GM part number for the Top Kick bracket to move the alternator to top passenger side of engine and ac pump to top driver side?

Thank you in advance for your help!

-Ben



Hello Ben,

Sounds like a great project. I also bought a 2001 HD 4x4 with an 8.1L and ZF 6-speed manual brand new when GM first came out with the zero percent interest after 9-11-01. It now has 53K miles and has been a great truck.

Here are my lessons learned.

1) I would replace the spark plugs, wires, and crank sensor and that’s it. These engines are simple and usually free of any oil leaks. The Early 8.1L crank sensors have a habit of failing so definitely get a new one. All crank sensors from GM parts have been superceeded to the new design. Once you put the 8.1L engine in an old truck you will not be able to replace the sensor without removing the engine so do it now. The sensors are around $65 but I don’t have the part number for it.

2) The Topkick/Kodiac/Workhorse high mount A/C bracket part number is 12558927. An L29 7.4L bracket looks similar but the bolts do not line up in the head. You will definitely need the 12558927 for a clean A/C installation. If you use the stock Silverado A/C bracket you will have to hack up your frame and that is not good. I don’t have the GM part number for the alternator bracket but the Workhorse part number is W0003928. You will have to get this through a Workhorse dealer not a GM dealer, although many Workhorse dealers are GM dealers. I work for Navistar, Inc which owns Workhorse.

3) I DO NOT recommend using the donor vehicles harness, electronic throttle control and pedal assembly. The best $600 you can spend on this project would be to order a new harness from Howell Engine Development as reworking an original harness is time consuming and you will never get it to run right nor will the harness look like a clean fit. Reworking a Silverado’s bused electrical center in the harness is a major hassle. For $600 Howell will also program your ECM to eliminate the electronic throttle, turn off EGR (take the EGR valve off and throw it away then make a cover for the hole in the intake or find a plate from a 2003 or newer 8.1L that had the EGR deletion from the factory. EGR was discontinued in 2003), turn off torque management and add a hot tune if you want. They can add provisions into the harness and program the ECM for electric fans if you want to go that route. Mine is programmed to a 91 octane hot tune that is supposed to be good for 450 HP and 550 Lb ft of torque. When you call Howell speak with Rob. This is probably the harness you want if you are running a 4L80E http://www.howellefi.com/customer/ge...e-by-wire.html

4) If you go the route of the Howell harness and ditch the electronic throttle garbage use a 1996-2000 L29 7.4L mechanical throttle body as it bolts right on but you will need a throttle body spacer for clearance for the throttle cable arm to swing. On the other hand, if you want cruise control the electronic throttle system is the easiest way to get it.
2629832586_a17a6757f1_z.jpg


5) I don’t recommend using the 8.1L exhaust manifolds as they will hit the frame on an older truck. Any big block header or exhaust manifold (396, 402, 454, etc) will fit the 8.1L.

6) I also do not recommend following the WyoTech instructors 8.1L swap recipe that can be found all over the internet in a PDF file. He did a lot of unnecessary work that he didn’t need to do.

7) You will need to rework the engine cross member to clear the oil pan. ORD’s HD engine cross member works great but I am not sure if it fits 67-72 4x4’s.

8) There is a small nub on the driver’s side of the engine that will need to be ground down just a tad so the engine mounts will bolt to the engine. At least that is what the saddle type engines mounts require. Not sure if the old style engine mounts will need this done or not. This will be an obvious thing you will see when you are installing your mounts.

9) One last simple thing, if you use an aftermarket tachometer you need to set it in 4 cylinder mode for it to read RPM’s correctly on distributorless GM engines.

Good luck. You will be thrilled once it is done!

Wow - great response - thank you!

I'm excited to get it this week.

I will probably be putting T400 & NP205 behind it.

Good call on crank sensor - mine went out in my '02 about 2 months after I bought my truck.

I'm using a DIY4x crossmember right now - not sure if it will fit - cross that bridge when I get there I guess!
wink.gif


I called Howell on Thursday last week - off recommendation of yours in one of your old post. They quoted $600 for harness +$200 to tune the computer.

Question I've been wondering - how did you plumb your AC to get from driver side top to passenger side firewall hook up?

Also wondering - if I'm using OEM '72 Factory tach - what do I need to do for that?

Thanks,

Ben



Wow, I am surprised they want an extra $200 over the cost of the harness. If I recall correctly, when I did mine the ECM programming was part of the harness cost. Maybe they changed their packaging or something.

A TH400 would work great behind an 8.1L but you may want to ask Howell if there is anything they can do to the harness in order to make the TH400 electric detent work more easily by tapping into the TPS signal. Not sure how you would get the TH400 electric detent work with an 8.1L otherwise.

As far as the A/C lines go, you’ll just have to have a hose shop custom make a set. My local Napa made mine.

There is a converter you can buy from MSD to make the factory tach work with a coil on plug engine. I ordered one and ended up sending it back once I figured out all I needed to do to my aftermarket tach was to set it on 4 cyl mode. This tach adapter should make your factory tach work with the 8.1L.

http://www.summitracing.com/parts/MSD-8913/

Chat with you later





So - ordered the two brackets I need:

$87.40 for the GM 12558927
$87.88 for the W0003928

Now -

Starting to get into this - and my 02 daily driver has been stumbling lately. Do you a code reader that you would recommend?


Any code reader should work to pull active codes. I am not sure if generic Autozone readers pull passive codes that do not trip a light though. A stumble could be low fuel pressure to failing plug wires or a coil. Hopefully, there is a code left behind to help steer you in the right direction.

Good to hear you got the brackets coming. I suspect both of these brackets will be discontinued though service parts before long.


Larry-

Two more questions:

1) What did you do with engine cross-member / oil pan clearance?

2) Do you know if I will need to alter anything or get different parts to get T400 to bolt up to 8.1?

Oh - and also - talked to a buddy who is old retired transmission mechanic. Asked him about the kick-down for the T400 - he said that the T400 has an electronic kick-down under the gas pedal. He said he would do the same setup -

So that when gas pedal is mashed, it hits the switch and kicks down tranny.

Thanks,

Ben



I used an ORD engine cross-member then added a ¼ plate steel under the engine mounts to space the engine up a tad bit more. The TH400 does indeed have an electronic detent. Most trucks had the switch near the carb but cars had them on the pedal. I like your idea of going with one that mounts to the pedal.
 
IGOR, your info is so helpful. Yes, u r nerd indeed. You opened a treasure box of info to help anyone becoming adequately aware about the 8.1 swap project.

Shovelbill80, I appreciate keeping attention to this Thread. In case you have more contacts and helpful info I'd welcome receiving more in this regard.

Gent's, you proven the value of this Site and not only the membership fees paid for itself, but its non-tangible value by far exceeded what's expected. Thanks to those active participants for their sincere desire to help and provide quality input. The support you are creating in here is priceless!
 
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This is good stuff. I plan to do the same heart transplant on my '91 when the time comes.. I'm very interested in any issues you've had to or will have to overcome.:waytogo:

K5_001.JPG
 
Hello Gen't, this is a web-link to an old Article (Surfing the Sand of Sahara in the Arabia) that I published in the Off-Road.COM website (2005), as I found it convenient to share with the thread-visitors while the subject project is ongoing:

http://www.off-road.com/atv/feature...sahara-in-the-arabia-11590.html?printable#eaf
--

Hope you will like it! A point for clarification is that all 'future-plans' that were discussed in this Article have been fully met; with even some more mods :) Take care.

REGARDS, AHMED.
 
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