Ok, so I have a new problem after installing new crate motor and fuel injectors. The car is performing fantastic when accelerating and idles like a dream, but when you are cruising at 15 mph car starts spitting and sputtering. If I power brake the car in drive around 1000 rps same thing happens. If the car is in drive and I give it a little throttle it is as smooth as can be. When I first took car out after install, I did get a code 42, 43. I just installed knock sensor last night and drove car today. Codes are no longer coming up, but car is still acting up. If you put your foot into it it ***** and gets with no stumble, it is only when you are around 1000 to 1500 rpms.
In the 5 years that I have owned the car, it has been a project so I had never driven the car on the road, not sure if issue was there before motor or not. It is an 85 L98 with no mods. I have replaced plugs, knock sensor, idle control valve, checked vac hoses, cleaned throttle body. I am thinking of replacing plug wires and cap rotor and maybe some other distributor parts just for fun. I hate throwing parts at it but I am getting frustrated and I refuse to take car to dealer due to being jerked around with a previous car with small issue that was never diagnosed.

 

Do you have timing set to 6* BTDC? Were the injectors you bought 24 lb/hr? They need to be, I think it was a one year only with the '85 that they used 24 lbs. If you bought different ones you will need a tune. It sounds like you may have bought smaller injectors.

I got a code 43 from using too high of an octane gas. Took a while to figure it out. That happened with 93, when I went to 91, it was all good.

What is the compression ratio with the new motor? It should be 9:1 as that is what stock is.

Does the cam have the same specs as the stock cam? If not, you will either need to swap back the original cam, or get a tune.

And the heads, were they the original heads that you put back on? Or were they the ones that came with the crate motor?

This kind of stuff isn't like it used to be with carbs, if you change something then the tune needs to be changed also.

 

Yes, timing is correct. I have checked the timing a few times just to make sure. I use the lowest octane in all my vehicles.... im cheap. I will check specs on motor, but its the 350/260hp crate motor from Jegs. I basically put my intake on and kept the motor the way it came from the company. Like I said, the motor is so smooth at idle and has nice power on take off, but cruising rpms... car doesnt want to hear it. I did notice when I ran the defrost this morning, that when given gas, that it sounded like the defroster got quiet which sounds like a vacuum issue.
Thanks

 

I like your idea of changing plugs and wires. If you've owned the car for 5 years and have no idea how long these things have been in the car, replace them just to rule out that possibility.

 

I think the problem is either in your cam, heads, or compression ratio.

The stock motor is 230 hp, not 260, so there is definitely a difference somewhere.

Can you post the motor specs?

 

I just had the company that I bought the injectors from tell me they are 21lb. Would 24lb make an improvement?

 

GM Goodwrench 350ci/260HP Engine & Packages





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This universal 350ci engine uses a brand new block and can be used as a replacement for most GM vehicles from 1973-85. It produces 260 HP and 350 ft/lbs torque with a 4-bbl carb and headers. It can be used as a replacement or as a retrofit into almost any vehicle. This new 350 crate engine comes with a GM warranty and is covered for 3 years or 100,000 miles in applicable GM vehicles only. JEGS has the GM Goodwrench Chevy 350 for sale at a great price!

Specifications
4-bolt main with 2-piece rear main seal
Cast iron crankshaft
LT1/LT4 powdered metal connecting rods
Cast pistons (dished)
Hydraulic flat tappet cam (.383''/.401'' Lift, 194 / 202 Duration @ .050'', and 112° lobe separation)
Cast iron cylinder heads with 76cc chambers
8.5:1 compression ratio
Block is compatible with left or right side oil dipstick (Requires Plug for Unused Side - Plugs are Included)
4-quart oil pan
Timing tabs for a 6-3/4'' or an 8'' balancer
Recommended spark plug: Accel #111-0574-4 or any spark plug with 14mm .460'' reach, 5/8'' hex, tapered seat, projected tip
Not Intended for Marine Use.

 

Definitely a big difference with that engine. The easiest and cheapest way to solve this problem would be to just put the carb back on.

That compression ratio is off. The motor you have is 8.5:1 compression, stock compression for 1985 was 9:1. So you would have to change your pistons to fix that or go with a smaller head gasket. Depending on the flow of your heads, that would also be a problem so you would have to swap out the heads to the stock heads.

The cam is a little wimpy, and definitely a low RPM cam.

The 85 cam spec are 202/206 @ 0.050", total valve lift 403/415 and LSA 114.5.

So that's way off. And lastly your injectors. You definitely need to get 24 lb injectors. Any time you change injector size, you have to change the injector offsets in the tune.

You have 3 options, the cheapest, put the carb back on, next cheapest and easy, buy a tuning kit and adapter for the ECM and get mail order tune, or lastly the expensive or longest, put all the original parts back on.

If I were you I'd just put the carb back on. This way you don't void the warranty or have to go through all the trouble here. Just unplug the check engine light.

 

I also like the idea of wires and plugs. I wouls also want to know what the fuel qualty is. If the car has been sitting that long fuel can be a issue. Another thing that happens is the TPS can can burnt areas right in the crusing zone because that is where it is at most of the time. That will give you the problems you are talking about. They are easy to test the problem is most people no longer have a analog ohm meter. It may be something you want to look at replacing if you can not test it. Some say you can test it with a dvom but I find it impossible to do that because you are looking for a clean swipping motion of the meter a DVOM with not let you do that

 

Even though the car was not on the road, I did start it and move it around the yard. I did pull the tank and replace the fuel pump about 2 years ago. So gas was always changed. Fuel filter was changed with injectors. Except for the small stumble, car seems to run great.
Motor never had carb.... dont even want to go that rout.

 

I agree would not even think about a carb. I would do plugs and wires and check into the TPS

 

You need a tune.

 

So lets hear more about this tune thing. I went over motor again, looking for vacuum leaks, changed wires, cap, rotor and module. Crazy thing... #1 wire looks like someone took a bite out of it from the exhaust. A little better but still has that slight stumble at around 1100 rpm. Outside of this area and the car runs great. It idles so smooth almost cant feel it running and no stumble on wide open throttle.
So whats entailed in tuning

 

Not sure if you checked your back pressure through your cat and mufflers. If this is the original cat and mufflers, this could be a problem as well. I would disconnect the mufflers from the cat and test. Had a similar issue with mine.

 

No Cat at all. Has O2 sensor and straight pipes right to new mufflers.

 

is this stumble at a cruise and giving it a little gas or is it hailing it at this point just a little more information

 

hey Hooked, if i give it more gas, it fixes the problem. For instance, going through a school zone at 15 mph, the car will act up until you give it more gas. Car idles sooo smooth, and accelerates great....