legend71

Looking for advice to fix my last few swap issues... I have a 94 LT1 w/80K into my 91RS, I did all the wiring and work using a 95 harness. The car has a slight and persistant misfire that is very evident when warm and under load. I it causes a shake when sitting at idle, also i believe the car is idling high @ 1200rpm as my 97 SS idles lower. I cannot scan the car, i always get no communication, but ive been scanning it as a camaro or trans am. Recently i learned that the PCM had a caprice/roadmaster knock module and i swapped it with an extra camaro one. I think it is a caprice PCM flashed to run my motor. In addition ive been looking at other peoples setups and they have added to my questions.

1. Should I scan my PCM as a Caprice to read the codes and/or do i need one from an actual Camaro/TA?

2. Suggestions on the misfire...it has spark and fuel, no vaccume leaks ive found

3. I used a corvette intake tube to run the MAF in a straight line to a 91Z28 duel snorkle, is this ok or is the 94 MAF so sensitive it needs the 90deg elbow and a cone shaped filter like everyone else does?

The car will spin the tire (have an 89 9bolt 3.27posi waiting in the garage) through second so i know there are not significant power issues, but its these last little things that are killing my MPG when im normal driving and not being able to scan is ticking me off. Any help is greatly appriciated. Thanks. Ill post pics of the completed swap soon.

Matt

legend71

Additionally is it true that an 91 RS fuel filter will not allow for good enough flow for the LT1? Today i filled my gas tank drove home, and it started spouting fuel... very confused as to what the heck is going on with this thing. I have an inline 255 fuel pump and the tbi in tank pump. Should i just put in a 91 z28 high performance intank pump? Many of these swap instructions give general ideas to solve the problem and i followed one path with interesting results

legend71

One more thing, after some further research it may have not been a good choice to throw the evap can out when i did the swap. Im not sure where the can is (trash probably) and i need to look tomorrow and see where i hooked up the fuel tank vent line. But again, the engine is so unpredictable, once i filled the tank with gas, the rpm idled @ 750 upon start for the first time then when warm went back to about 11-1200 and when i got home thats when the gas began spewing out of the tank near the cap. it makes this mess whenever i fill up.

jakemussman

iTrader: (3)

I thought the tbi pumps don't put out enough pressure to run an lt1?

legend71

It runs rough with it, I have an inline airtex that puts out around 40-60psi and 35gph. I think that should do it... I see you have a similar swap, what did you do for your fuel pump? What fuel filter did you use. Also we're there any gotchas that you found? I am very close with this dang thing

jakemussman

iTrader: (3)

41-47 PSI should be plenty. I used the stock fuel lines, filter, and pump that came stock in my car as a 3.1 V6. So you have confirmed the fuel pressure at the rail?

legend71

Yeah fuel pressure is good, I figured out solution to the fuel tank vent. I used a brake booster check valve and some fuel hose. No tank pressure issues anymore. Im slowly diagnosing my misfire. I used a spray bottle to test each header primary and the water sits on #2 and slowly evaporates where on all others it vaporizes. There is no noticeable difference when i run the car with #2 plug disconnected. The plug is not fouled nor is it white so im at a loss with that. Im also trying to get the damn thing to scan still in hopes to read the codes.

legend71

Sorry Jakemussman, i should have double checked, I am only making 35 psi at the rails... no change during acceleration or anything. All but one spark plug are white indicating a lean issue. so it makes sense now, misfire and all.

Can i buy a z28 fuel pump and put it in the TBI RS tank? I feel like i read i need to swap tanks...

cprmn14

iTrader: (3)

Theres no way that TBI fuel pump is close to supporting your LT1, I picked up a Walbro 255lph for a 91 Camaro. I heard that they sold out to a cheaper company a few years back but I havent had any problems with mine yet.

legend71

I'm actually running 2 pumps. The stock and an inline airtex. That's why I'm disappointed

86White_T/A305

maybe you have a bad injector on #2 cylinder,or double check the plug wire for loose fit on the spark plug causing a slight miss.is the pcm obd1 or 2?

25th327RS

iTrader: (2)

Agree, the white plug on misfiring cylinder indicates lean, and is most likely a bad injector or faulty wiring. Swap injectors with another cylinder and see if the problem moves to the same cylinder or not.

legend71

It's OBD I, after going through all the plugs #2 is the only one that looks healthy. The others all show signs of running way lean. All of the injectors are getting pulse.

84redta

iTrader: (34)

Your inline pump is probably starving your TBI pump as it cannot pump fast enough to keep up, that is part of your problem that you could go without seeing until you have a full throttle experience. Should just have an in-tank 255 pump, don't need any special tank or any special sending unit. I got mine off ebay and it's been running great for two years through a stock 3rd gen fuel filter just fyi.

Also, I would lean towards a bad injector if the plug keeps fouling and you have 0 resistance on the plug wire. I mean it could be a bad cap I suppose, when was the last time that you did a tune up to the Opti?

legend71

Thanks for the pump info that helps a ton. Ill get a 255lph pump then go from there. The opti, coil, wires and plugs are all new. The injectors are old but ill post the pics of the plugs. Again #2 looks like normal with carbon even on it. The rest are white and look like pre detonation or lean.

legend71

Here's most of the plugs look like. I assume from running at 35 psi

legend71

Here is #2 the only odd one out

legend71

Just to show you guys what I'm working on. This is after cutting my coils. Not sure what brand they are, they are blue though. We're on the car when I bought it

BCdawg57

iTrader: (1)

How do you know the caprice PCM was flashed for an fbody? I don't know for sure, but its possible the PCM may be the reason you are running lean. If you know anybody else with same year fbody as the motor, swap the PCM out and see what happens.

five7kid

iTrader: (14)

While I agree fuel pressure is important, the stock TBI pump would have to be almost dead to be a problem in this setup, assuming the in-line pump is up to the task.

Pump output is a combination of volume and pressure. The higher the outlet pressure, the less the volume compared to a lower outlet pressure. The outlet pressure is built up by the restriction at the other end of the line, not at the pump itself. The in-line pump should basically make the outlet pressure at the in-tank pump zero.

Note that pumps are flow rated at zero psig outlet pressure - i.e., "free flow volume". So, while a Walbro 255 may be able to pump 255 liters/hour "free flow", i.e., zero outlet pressure, it won't be able to maintain that volume at 50 psig, for example. Likewise, a TBI pump will be able to produce 50 psig outlet pressure, but it won't be able to maintain that pressure while supplying the same volume it could at the stock TBI 12 psig pressure.

FWIW, my son has a 2001 S10 Blazer that had an LS engine swapped into before he got it. On the dyno, it was leaning out and losing pressure with the in-line pump they had installed (they had removed the in-tank electric pump). He put a new stock-replacement 4.3 pump and pickup in it, kept the in-line pump they used, and the problem went away. Pumps push better than they suck, which is one of the reasons the factory went to in-tank pumps, and why the in-line pump was able to keep up after the in-tank pump was put back in.

Bottom line: I'd verify your fuel pressure under the conditions in which the car is acting up before going through the trouble of replacing the pump. An in-tank Walbro 255 is a good setup, but may not solve the issue you're having if it isn't being caused by inadequate fuel pressure.

legend71

Im not sure if the person who flashed it did do it right. I told him what i wanted for my application, paid, and received the PCM in the mail. I have the original PCM sitting in my garage but i have no way around vats

legend71

That makes alot of sense. Is that why the fuel pressure regulator is at the end of the rail? Also i was advised to put the inline pump near the tank but i was too impatient. However, I ordered an LT1 hotwire fuel pump kit from hawks and Im going to install it the same time i do my 9 bolt swap next weekend. It'll eliminate the fuel pump clutter from the engine bay anyway. I really dont know how to diagnose this without being able to scan the car. I may have to send the stock PCM to someone on here to have the vats deleted. I was thinking about purchasing the Tuner Cat LT1 package to do it myself for about $100 more than getting it reflashed. I have another intake sitting around from a 96 roadmaster with injectors on it that i could try swapping out but they are in rough condition vs the ones on the car now which are not rusted. Im going to double check for spark and pulse all around this weekend, but im already confident as ive checked before. Maybe #2 has weak spark? if thats possible?

legend71

Additionally I am using fairly new (purchased a few months ago) Autolite XP plugs if you guys know if they are any good or not

legend71

Well i got my racetronix pump, and hotwire kit from hawks today, I stupidly ordered the LT1 version instead of the thirdgen version not thinking and after looking at it, i dont think ill have any problems making it work fine. This weekend I will install the pump...

Id like to bypass and eliminate the stock fuel pump relay if possible. It seems like thats what the hotwire kit essentially does.

I will take out the inline airtex pump if someone needs one... I wouldnt want much for it.

Also i will be installing my 89 formula 9bolt that i sanded and painted. A new proportioning valve from hawks and some new swaybar bushings.

Thanks to wiring info i found that Pocket wrote, Im going to rewire the car this weekend as well. I learned a better way to hook up the ALDL port from it so hopefully ill get a scan finally.

Finally i need to find a trust worthy source to pay for a computer reflash to ensure its done right.

If the pump and computer dont work ill get some new injectors but im hoping rewiring and a computer reflash will allow me to scan the car

legend71

Decided to overnite the thirdgen hotwire kit and pump instead and send the other back. Less complicated

legend71

I have the Racetronix pump in, the hotwire kit installed and the 9bolt is all hooked up. Im now making 41psi at the rails and reving it goes up to 45. My disk brakes work great, installed the proportioning valve from Hawks. I think I still have a slight misfire and the check engine light still comes on when warm. I can do two wheeled burnouts now though and the car accelerates like a rocket compared to before.

Im going to rewire it this weekend and attempt to scan it again. If it doesnt work Ill send my PCM to get flashed. Ill post some pics of the install tonight or tomorrow. The Racetronix kit was extremely straight forward and the rear swap was easy. The worst part is getting the gas tank out on foot tall jack stands with my flowmaster exhaust not wanting to unbolt.

Strick1

Hey Legend, Good thread. This has given me good info on my LT1 to 3rd gen swap. My plan is now to replace my 83 non TPI tank with a 4th gen plastic tank with the in tank pump. That should take care of my fuel problems. Now if I can only figure out how to fit the LT1 A/C compressor in the K-member.

legend71

The plastic tank is a good plan. The thirdgen one was a pain and pretty sure I screwed up my exhaust pushing it out of the way. You need to find pictures of where people pound the k member with a hammer...

Strick1

Once I get the LT1 and the K-member out, I'll be able to see where I'll have to modify the K-member. Everyone says to use the 3rd gen motor mounts, we'll see what fits.

legend71

Yes the block for the LT1 has mount holes in the same location as the thirdgen motor so just use those. The LT1 mounts are in a different spot on the motor