Tbi swap build thread

[Chad77]

Hey rfmaster, I have been playing with my ride and well it runs awesome expect at idle it just wont idle its too low. I don't have any leaks I have checked ! I thought I read some where something about resetting something?

[rfmaster]

Originally Posted by Chad77

Hey rfmaster, I have been playing with my ride and well it runs awesome expect at idle it just wont idle its too low. I don't have any leaks I have checked ! I thought I read some where something about resetting something?

Yes, IAC reset - search thread for IAC reset (perhaps we should make it sticky how to do it). The alternative is to increase minimum idle with adjustment set screw (covered by the temper resistant plug )

//RF

[Chad77]

Well I went and bought a TBI gasket kit including the pressure regulator put everything together and now idles in park and in gear at 250 on the tack, but when its warmed up and idling in gear and I get on it she spits and sputters a little. I am sitting at about 4* with the timing.

[rfmaster]

Originally Posted by Chad77

Well I went and bought a TBI gasket kit including the pressure regulator put everything together and now idles in park and in gear at 250 on the tack, but when its warmed up and idling in gear and I get on it she spits and sputters a little. I am sitting at about 4* with the timing.

IRC you have a 283 of unknown origin! IE, it would be nice to know what cam and compression that motor has. One thing that you should do is to get the cast number of your heads. This way some timing adjustments can be made. Since the 283 was never offered with EFI there are no OE chips, but DIY tune can be done if you are willing to invest in your setup (money and time).

250 on the tach ??? That's a bit low??

//RF

[Chad77]

Iam sorry I failed to tell you I found out the vacuum on the 283 was to low to run the TBI so I ended up swapping in a 350.
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[Chad77]

Ok I got to take my truck out on the road.... Hope you can help, I ease into the pedal Iam fine on take off, but if I get into it she spits sputters back fires through the TBI and if I stay in it it will die. when Iam running at about 45mph and I kick it down she studders and then goes. When Iam sitting their Idling in park I can rev and their is no problems.?.?.

[rfmaster]

Originally Posted by Chad77

Ok I got to take my truck out on the road.... Hope you can help, I ease into the pedal Iam fine on take off, but if I get into it she spits sputters back fires through the TBI and if I stay in it it will die. when Iam running at about 45mph and I kick it down she studders and then goes. When Iam sitting their Idling in park I can rev and their is no problems.?.?.

I'll need additional details about your ride to provide any troubleshooting recommendations worth your time.

So far - you have 350 CID motor (I assume it is stock??) - details please it is very important to know what we are trying to work on.
Trany - THM-350??
VSS = Yes or no.
Verified fuel pressure 13 PSI with engine idling???
ECM 1227747 with BCC code (ASDU or ???)
Do you have functional SES light?
Do you have functional P/N switch??
MAP sensor connected to back port of TB (only MAP sensor can be connected to that part nothing else),

//RF

[Chad77]

So far - you have 350 CID motor (I assume it is stock??) Yes


Trany - THM-350?? Yes
VSS = Yes or no. NO
Verified fuel pressure 13 PSI with engine idling??? Unsure on how to check
ECM 1227747 with BCC code (ASDU or ???) where do I find the BCC ?
Do you have functional SES light? YES
Do you have functional P/N switch?? Whats this?
MAP sensor connected to back port of TB (only MAP sensor can be connected to that part nothing else), MMM I have it on the front left port and the trans is hooked on the rear port.

[rfmaster]

Originally Posted by Chad77

So far - you have 350 CID motor (I assume it is stock??) Yes


Trany - THM-350?? Yes
VSS = Yes or no. NO
Verified fuel pressure 13 PSI with engine idling??? Unsure on how to check
ECM 1227747 with BCC code (ASDU or ???) where do I find the BCC ?
Do you have functional SES light? YES
Do you have functional P/N switch?? Whats this?
MAP sensor connected to back port of TB (only MAP sensor can be connected to that part nothing else), MMM I have it on the front left port and the trans is hooked on the rear port.

Take a look at your TB, in the back. Between inlet and outlet fuel ports there should be 1/4" vacuum port. Connect MAP sensor vacuum line to it. Nothing else can be connected to this port! For transmission vacuum modulator use intake vacuum port - there is usually one port available tapped into #8 cylinder intake runner. It usually used for power brakes booster and transmission vacuum modulator. Front vacuum ports are not suitable vacuum ports for MAP sensor.

BCC is printed on the ECM service label along with service part number - 1227747. If this label is missing you can remove EPROM cover plate (2x 1/4" sheet metal screws) and read BCC from EPROM label. However, this is not critical at this time.

P/N switch stands for Park/Neutral switch and tells ECM if trany is in Park/ Neutral or in Drive - ECM will increase idle RPM when gear selector is moved into drive to prevent engine stall.

Since you have 350 CID engine - you better have 62 lb injectors - right???

Do you have EGR??

//RF

[1984 t type]

I used the search feature and found this thread, man is it awesome! I started at the beginning and made it to page 9 before skipping to the last page praying that this thread was still alive. I have an 85 k20 suburban with a 350 and swapping out the manual trans for a rebuilt 700r4, was going yo do the 5.3 swap but it's just not for me right now. Anyways I'm going to pick up a 91 1500 suburban parts truck after work and going to start my swap this weekend hopefully. I'm going to go back and read over the 21 pages I just skipped but I'm sure I will have a few questions for you guys along the way and were just wondering if you guys were still here
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[68 TT]

Originally Posted by 1984 t type

I used the search feature and found this thread, man is it awesome! I started at the beginning and made it to page 9 before skipping to the last page praying that this thread was still alive. I have an 85 k20 suburban with a 350 and swapping out the manual trans for a rebuilt 700r4, was going yo do the 5.3 swap but it's just not for me right now. Anyways I'm going to pick up a 91 1500 suburban parts truck after work and going to start my swap this weekend hopefully. I'm going to go back and read over the 21 pages I just skipped but I'm sure I will have a few questions for you guys along the way and were just wondering if you guys were still here
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With a square body to square body swap with both being Suburbans your swap should go fairly smooth.

Good luck and keep us updated.

[rfmaster]

Originally Posted by 1984 t type

I used the search feature and found this thread, man is it awesome!
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Thread is still alive - we just enjoy driving our trucks during nice weather!

Since you have a 91 donor for your swap it will make conversion easier. Couple of issues that I see for you - are you planning to keep 4 wheel drive system in your 85 K20? How much of the 91 drive train are going to swap into 85???.

//RF

[1984 t type]

I'm keeping my entire drivetrain just using all of the tbi stuff of of the donor truck, was gonna take the heads and intake but this truck has blown head gaskets so I may just use an adapter plate on my intake. What problems did you forsee with my swap ? I do know that the donor truck is 4x4 but I'm not sure if it has a 700r4 in it or not but I just assumed that a 91 would
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[68 TT]

Originally Posted by 1984 t type

I'm keeping my entire drivetrain just using all of the tbi stuff of of the donor truck, was gonna take the heads and intake but this truck has blown head gaskets so I may just use an adapter plate on my intake. What problems did you forsee with my swap ? I do know that the donor truck is 4x4 but I'm not sure if it has a 700r4 in it or not but I just assumed that a 91 would
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Your 91 V1500 should be a 700R4/4L60 with an electronic speedo NP241C transfer case. You will need to swap in both the trans & transfer case along with the gauge cluster as the speedo is electronic and not cable like your 85.

The computer may not like the cam in your 85 very much so you will probably need to do some tuning once you get it running. The VE of the older heads and intake are bound to be quite different than the TBI parts too. Nothing a little quality time with TunerPro RT won't fix.

[1984 t type]

How do I go about keeping my older 700r4 in it ? It's freshly rebuilt with 0 miles on it
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[68 TT]

Originally Posted by 1984 t type

How do I go about keeping my older 700r4 in it ? It's freshly rebuilt with 0 miles on it
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Did you already do the manual trans to auto trans conversion?

If not then the transfer case of the 85 manual trans in the K20 should be a large fine spline that won't allow the older small fine spline 700R4 / 4L60 to bolt up to it. It could also be a large 10-spline setup if somebody retrofit an older SM465 & transfer case into it some time in the past but neither will fit the 700R4.

You will have the small fine spline transfer case you need to do the 700R4 / 4L60 conversion with the 91 V1500 parts truck. The NP241 in it is an upgrade over the NP208 as well with a stronger chain design and a few other upgrades.

Your older 700R4 will bolt right up to the transfer case in the 91 and the driveshafts should be close to the right size for you too. You will have some differences in the rear section of the rear driveshaft with the 14-bolt vs. the 10-bolt rear axles. You should be able to put the back half of the 85 driveshaft onto the front half of the 91 rear driveshaft to make a hybrid length version to bolt the 700R4 / NP241 to the 14-bolt in the 85.

It will simplify your TBI conversion too as all the wiring and ECM is set up for the non-mechanical speedo pieces in the 91.

[1984 t type]

Is the spline count different on a newer 700 and 241 transfer case
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[Jonboy]

I don't think so. The 208 and 241 transfer case are pretty similar, save for the speedometer drive.

If you don't want to swap those out, JTR sells a VSS that is driven by the speedometer cable. I went that way on my swap; the part is $75.

[1984 t type]

Thanks guys. Look at me flooding you guys with questions and I haven't even picked up the doner truck yet, man 4:00 is taking forever to come I feel like a kid on Christmas eve !
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[1984 t type]

I have not put my automatic trans in yet but I did pull the manual out, it was a 456. I got my 700r4 and transfer case out of a 86 k blazer then sent the trans out to be rebuilt, I also made sure to get all the linkage. On another note picked up my parts truck yesterday and man is the interior nice, paid 450 for it and it actually runs but it needs new head gaskets. Should I send the center bolt heads out to the shop and use those heads and intake off the 91 or should I just use what's in my truck now with an adapter plate? I am trying to keep this a low cost swap but want to do it the right way. Not looking for power but reliability and mpg's as this will be my new daily driver.
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[rfmaster]

Originally Posted by 1984 t type

I have not put my automatic trans in yet but I did pull the manual out, it was a 456. I got my 700r4 and transfer case out of a 86 k blazer then sent the trans out to be rebuilt, I also made sure to get all the linkage. On another note picked up my parts truck yesterday and man is the interior nice, paid 450 for it and it actually runs but it needs new head gaskets. Should I send the center bolt heads out to the shop and use those heads and intake off the 91 or should I just use what's in my truck now with an adapter plate? I am trying to keep this a low cost swap but want to do it the right way. Not looking for power but reliability and mpg's as this will be my new daily driver.
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The center bolt heads on your donor are commonly known as a swirl (193) heads. If you look into intake port under intake valve you'll see a ramp that forces intake air to swirl.



Great concept except that it causes air flow restriction at higher RPM's which is not an issue for truck engines. IMHO, I would rebuild or fix 91 engine vs 85. The 91 block uses single piece RMS which almost never leak vs. split 2-piece seal used in 85 block. Also, the 91 block has provisions for a roller cam - cast bosses for the roller lifter retaining spider and machined cam thrust retention plate in front. If you ever choose to go to roller cam the conversion is matter of sourcing parts.

What you have to figure out why head gasket failed - most of the time it is due to head warping. These heads do not have enough material in right places and if subjected to prolonged high outputs tend to warp. If overheated they crack between two center adjacent exhausts ports. Before spending time or money on these heads have machine shop magnaflux them to make sure that there are no cracks. I have thrown out probably 3 or 4 sets of heads last year for cracks.

Older heads (from your 85) will bolt to your 91 block. 91 Intake manifold will require minor filing of 4 inner bolts - the angle changed from 45 to 72 degrees. Round file does the trick.

Stock ECM calibration can be used as a starting point to run this engine. However, as 68TT mentioned this will not be optimum due to spark advance (SA) and volumetric efficiency (VE) tables in your ECM setup for a 350 with swirl heads. ECM parameters can be easily changed by altering appropriate tables and burning new chip for your ECM.

Let us know what you find - do not rush into it - ask questions.

//RF

[1984 t type]

My 85 block runs like a dream and I'm on a budget so rebuilding the 91 block is not an option at this time. However I will take the heads to the machine shop and see if they are any good. Was planing on pulling my 85 block out to clean and paint the engine bay and block, so while it's out I will change all the gaskets and rear main seal also gonna check the freeze plugs. If I do use the 91 heads on the 85 block will I still have to get a new chip
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[68 TT]

Originally Posted by 1984 t type

My 85 block runs like a dream and I'm on a budget so rebuilding the 91 block is not an option at this time. However I will take the heads to the machine shop and see if they are any good. Was planing on pulling my 85 block out to clean and paint the engine bay and block, so while it's out I will change all the gaskets and rear main seal also gonna check the freeze plugs. If I do use the 91 heads on the 85 block will I still have to get a new chip
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You could put the tiny cam from the TBI engine into your 85 block with the 91 heads & intake on it then the ECM wouldn't know the difference. This would get you on the road for the least amount of money if the cam is in good shape and the heads were good. It will be a toss of the dice as to the condition of the TBI cam lobes though and with a blown head gasket or possibly cracked heads I don't think this is a budget frinedly approach for you.

If your cam is not too big in the 85 engine then it will end up being cheaper to just put a TBI adapter plate on the 85 intake and buy the stuff to burn your own prom chips rather than put out the cash to rebuild the TBI heads.

I would go with a new computer friendly cam & lifters with more lift & duration than the TBI cam if the one in your 85 is too aggressive. The stock TBI cam is ridiculously small and I wouldn't spend the money to buy a new stock replacement one.

The TBI intake does not flow well at all and will be a hindrance even compared to the stock 85 Q-Jet intake so don't waste your time or a set of intake gaskets to make the thing fit your 85 heads.

You will want an ALDL cable and the TunerPro RT software anyway just to monitor your engine so all you really need to buy above the basics is a chip burner like you will find on moates.net

A little quality time tuning the ECM to the 85 engine won't cost you anything but time and a bit of gas. The guys on thirdgen.org have documented all the tuning procedures very well so they are a great learning resource.

[rfmaster]

Further to 68TT point

If you have a factory cam (or even a mild RV cam ) in your 85 350 stock TBI calibration is robust enough to run that engine. Once you get it going and driving you'll want to dial in the combo for a better performance which will require, as 68TT put it " Quality time with TunerPRO ". You'll be surprised how much performance can be attained after you are done with it. Just keep this in mind stock TBI cam has 179/194 deg duration at .050" and maximum valve lift with 1.5:1 rocker ratio is .350/.384 - pathetic for all practical purposes.

For a factory or mild RV builds my basic rule of thumb is - if it idles STEADILY around 650-700 RPM with 14 to 16 in-Hg (or better) stock calibration - (ASDU) is good enough to start with and run. The biggest hindrance to TBI is large overlap camshafts with tight LSA <112 deg. Tighter LSA and large overlap throws too much unburned intake charge into exhaust, at idle, causing false lean condition.

If you are looking for a mild flat tappet camshaft MT-2, CS-1014R, Crane CRN-113904, Edelbrock Perfomer 3702 and many others have been tried and are known to work with basically stock TBI calibrations.

//RF

[1984 t type]

Ok so I'm going to go with the adapter plate with the 85 intake and heads. Is there going to be a special bracket for the tv cable ? Just trying to get my parts lined up
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