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Sierra TBI fuel injection conversion - Success & pitfalls
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Author:  johnmath [ Thu Jun 13, 2013 2:33 pm ]
Post subject:  Sierra TBI fuel injection conversion - Success & pitfalls
I recently completed installing a TBI setup from a '92 G16B Swift engine on my '88 SJ50 Sierra. The conversion was easy enough and the results are very good. I gained about another 10 kph speed going up the steep climb of the South Eastern Freeway from Adelaide, but I have yet to measure mpg. The engine idles properly (first time ever), starts easily when cold, revs better and is overall very smooth and flexible. However I did strike a few problems doing the conversion:

1. The donor car was a overhead cam with a different bore distributor shaft also designed to turn in the opposite direction! Solution: I used the original Sierra distributor but removed the mechanical advance balance weights and clamped the vacuum advance turret, removed its internal ignitor and wired its pickup coil to the plug off the Swift distributor. Works a treat.

2. The fuel pressure was far too high - around 50 psi instead of under 20. CO was well over 10 and the A/F below 11 (very rich). This was because of flow restriction in the return fuel pipe. Solution: I replaced the original return fuel pipe with a piece of 6 mm IB copper pipe. Turns out that the internal bore of the original return pipe is barely over 2 mm. You might be lucky if you use a low flow/pressure fuel pump, but I installed a fairly standard Bosch external one, and it needs a bigger return pipe.

3. The ECU is programmed for a bigger swept capacity of 1.6 versus 1.3 liters, and an 16 valve engine with better volumetric efficiency. The Sierra swept capacity is about 80%, but its power output is only about 70% of the donor engine (some of the difference in power is that it peaks at lower rpm). That means that the ECU will deliver too much fuel. Solution: I used a variable 10,000 ohm potentiometer (trimmer resistor, cost $2.25 from Altronics) to trim the output of the MAP sensor to 75%, so the ECU thinks it is getting only 3/4 as much air going into the engine. Results: CO 1.7, CO2 14, O2 0.2, NO2 (after cat) 0, HC 200 ppm, Lambda 0.98 and AF low 14s. The mechanic who did the test couldn't believe it! I didn't even need to trim the adjuster.

4. There is no speed sensor in a SJ50 Sierra. Solution: hot glue a magnetic reed switch near the rotating magnet in the speedometer. The speed sensor isn't vital, but can improve fuel economy slightly.

Also while the dashboard was out, I put a bulb in the "Check Engine" warning light socket and hooked that up to the ECU. This light will come on if there is a fault and can be used to diagnose the problem by shorting the test plug diagnostic pin to ground, and counting the flashes off the check light. Code 1 2 = OK, 1 3 = O2 sensor fault, 1 4 = coolant sensor fault, 2 1 = throttle position sensor fault, 2 3 = inlet air temperature sensor fault, 2 4 = vehicle speed sensor fault, 51 = exhaust gas recirculation fault.

You might ask why go to the trouble of a TBI conversion on a G13A Sierra when it is probably less trouble to drop in a G16B? The smaller engine will always have the potential for better fuel economy because of it's lower friction and lower thermal losses through the smaller bores. Combined with extractors, the engine pulls quite well. A 16 valve head would give more top end power, but for off 4WD off road touring, that is no particular advantage. The engine was rebuilt just before I bought the car too, so I wanted to keep it. I'll post some fuel consumption figures in a couple of weeks.

EDIT: reference to twin cam removed.
Author:  Fatzook [ Thu Jun 13, 2013 3:15 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
Nice write up. If you have pics to go along with this, I'd suggest a move to the 'Good tech' section.
Author:  want33s [ Thu Jun 13, 2013 3:29 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
1, Good work.
2, Usually you run a new fuel line and use the old one as the new EFI return.
3, Brilliant!
4, ok.

If you lug it up a hill till it stalls, how hard is it to restart?
Author:  31zook [ Thu Jun 13, 2013 4:20 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
How did you fix the cold start?
Author:  dono1 [ Thu Jun 13, 2013 7:23 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
Pics please! I'm in the middle of doing a tbi setup from a charade.
Author:  johnmath [ Thu Jun 13, 2013 8:05 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
31zook wrote:
How did you fix the cold start?


It's all handled by the ECU, so as long as all of the sensors and actuators are in place and working, it just works.
Author:  johnmath [ Thu Jun 13, 2013 8:06 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
dono1 wrote:
Pics please! I'm in the middle of doing a tbi setup from a charade.


I didn't take pics whilst I was doing it, but I can take pics of specific things and post them. Tell me what you want to see.
Author:  johnmath [ Thu Jun 13, 2013 8:08 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
want33s wrote:

If you lug it up a hill till it stalls, how hard is it to restart?


Why would it stall?
Author:  joeblow [ Thu Jun 13, 2013 8:36 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
johnmath wrote:
want33s wrote:

If you lug it up a hill till it stalls, how hard is it to restart?


Why would it stall?


Because girly manuals do that offroad. By the way the engine it came off was a single cam....not twin.
Author:  fordem [ Fri Jun 14, 2013 8:04 am ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
I don't think Suzuki ever made a twin cam G16
Author:  droverdave [ Fri Jun 14, 2013 9:02 am ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
Either way its a damn good effort, well done johnmath.
Author:  want33s [ Fri Jun 14, 2013 9:15 am ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
johnmath wrote:
want33s wrote:

If you lug it up a hill till it stalls, how hard is it to restart?


Why would it stall?


I had TBI on my 1.3 ages ago. Ran great, upside down even. Turn it off it would start fine but if I stalled it for whatever reason it was a bitch to start.
Carried on like a carby with a stuck needle flooding, would wind and wind and eventually if given full throttle would cough cough cough rev.
Author:  johnmath [ Fri Jun 14, 2013 6:03 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
want33s wrote:
johnmath wrote:
want33s wrote:
I had TBI on my 1.3 ages ago. Ran great, upside down even. Turn it off it would start fine but if I stalled it for whatever reason it was a bitch to start.
Carried on like a carby with a stuck needle flooding, would wind and wind and eventually if given full throttle would cough cough cough rev.


I am going to try to avoid the upside down test, but I'll be doing a lot a difficult and steep climbs. Will let you know how I go...
Author:  want33s [ Fri Jun 14, 2013 6:31 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
johnmath wrote:

I am going to try to avoid the upside down test, but I'll be doing a lot a difficult and steep climbs. Will let you know how I go...


Sorry I wasn't clearer but mine did it ANYTIME it stalled whether it was on a hill or level ground. The engine never stalled by itself due to any fault, it was all driver operation.

Try it with yours.... standing start in 3rd gear should do it.
Author:  johnmath [ Fri Jun 14, 2013 6:46 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
want33s wrote:
johnmath wrote:

mine did it ANYTIME it stalled whether it was on a hill or level ground.

I think you may have had a faulty CTS (coolant temperature sensor) so the ECU was giving fuel enrichment thinking it was a cold start....
Author:  johnmath [ Fri Jun 14, 2013 11:54 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
joeblow wrote:
johnmath wrote:
want33s wrote:

By the way the engine it came off was a single cam....not twin.


Yeah silly me - i thought a 16 valve would be a DOHC, because a 16v SOHC is about as much sense as a one piece bikini!
Author:  Rhinoman [ Sat Jun 15, 2013 5:09 am ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
want33s wrote:
I had TBI on my 1.3 ages ago. Ran great, upside down even. Turn it off it would start fine but if I stalled it for whatever reason it was a bitch to start.
Carried on like a carby with a stuck needle flooding, would wind and wind and eventually if given full throttle would cough cough cough rev.



Bit late now but if you'd spun it over first at full throttle it should have gone into flood clear mode. Then it should have started OK afterwards.
Author:  fordem [ Sat Jun 15, 2013 5:10 am ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
Actually, by definition, bi means two, so if it's a one piece it's a monokini, and from what I'm told the 16V SOHC heads breathe better than both the 8V SOHC & 16V DOHC heads (for the G13), so a 16V SOHC head makes a lot of sense. :wink:
Author:  johnmath [ Thu Jun 27, 2013 4:30 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
Went to Kangaroo Island camping for a few days over the weekend and did quite a bit of low range off road driving over very difficult terrain, fully loaded to the gunnels and about 60 kgs on the roof racks. Best economy 10.6 kpl (30 mpg for old farts like me), worst economy 10.0 kpl. Front left brake is dragging a bit pulling car to the left, so there might be better economy when I get the callipers rebuilt. Speed going up very steep hills is up by 10+ kph. Engine starts and runs perfectly in all conditions - hot / cold / stalled / whatever. A finger wiped inside the exhaust pipe comes out clean! Overall I am very pleased and wish I had done the TBI conversion years ago.
Author:  johnmath [ Sat Jun 07, 2014 9:08 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
Fitted a new O2 sensor a while back and now consistently get >11 kpl around the city/short runs. That's a 40+% improvement on the old carby days when I used to get 7.8 around town. I will do one last long touring run next week before I (sadly) part with this vehicle.
Author:  johnmath [ Tue Jun 17, 2014 9:56 pm ]
Post subject:  Re: Sierra TBI fuel injection conversion - Success & pitfall
johnmath wrote:
Fitted a new O2 sensor a while back and now consistently get >11 kpl around the city/short runs. That's a 40+% improvement on the old carby days when I used to get 7.8 around town. I will do one last long touring run next week before I (sadly) part with this vehicle.


Weekend run mix of highway 110, dirt roads and a bit of off road 4WDing from Adelaide to Southern Flinders and back got 13.3 kpl = 7.5 lt/100km or 37.7 mpg in the old money. So that's around 45% improvement in economy around the city and 33% improvement on long trips.
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