QuestionQUESTION: This is going to be a tricky question. I have a 350 crate motor out of a '76 blazer. We added an intake from an '88 2wd suburban with a 350 and the tbi to it. We are only running the computer for the tbi and nothing else. We cannot get the correct timing on the motor, and or the motor runs rich and back fires. The truck will idle for about 2 minutes then starts to studder. No extra high performance accessories, everything is stock. How can I check sensors on the tbi, or is replacing them my only option? Tranny is a th350. This is all in a toyota pick up.
ANSWER: Sergio,
Well, it is a tricky question, but it actually has a fairly simple answer. I take it you are using the suburban's computer to run the injectors, which in theory would work, but you are not getting any signal from the external sensors that are required to run the fuel system. You need input from the O2 sensors, the throttle position sensor, cam position sensor, and a host of other stuff that makes the system gel together. My advice would be if you want to run injectors, go for an aftermarket system that is a stand-alone to run the TBI. Other than that, probably a carb is going to be your best (and least expensive) bet.
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QUESTION: The motor is running the o2, map, tps, and temperature sensors. I have already replaced the engine coolant temp sensor, and the o2 sensor which had minor changes to the way the motor ran. Do I maybe have the vacuum lines backwards, and if so which ones do I need and don't need? Thanks for any help.
ANSWER: Sergio,
Well, there are a couple of other things to check here. Did the crate motor have a vacuum advance distributor, or electronic? You may be getting constant vacuum to the distributor if it is a vacuum advance. you can check this by putting a finger over the hose and see if it gets steady vacuum or more as the motor revs. If it is getting steady vacuum, the distributor is reading it as high rev and is advancing the timing to the point it won't run at idle. If this is the case, you'd have to go with an electronic advance distributor, or an aftermarket setup. Also, a parts store like a NAPA or something should be able to bench test your injectors to see if they are working properly or if they are stuck wide open. Let me know how it works out, and if it doesn't, I'll see if I can come up with anything else.
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QUESTION: I apologize, I should have said that the distributor was from the same suburban. I know that we've messed around with the vacuum lines, and have actually had fire come out of the carb. If it were the injectors, what would I be looking at as far as price? If I can't get this going I am actually thinking of just running the carb again, and maybe buying a propane setup later.
AnswerSergio,
If you are having fire come out of the TBI setup, then you are definately looking at some sort of timing issue. Usually it will pop through the carb when it is a tooth or so, or 180 degrees off on the distributor. Backfiring through the carb is generally a consequence of the cylender firing with the exhaust valve open; which would explain the popping and fire in the carb, and not being able to get the timing right. I would suggest taking the number one cylender spark plug out and bumping the starter with your finger over the hole till you feel the air whoosh out of it and then getting top-dead-center bu turning over the motor by hand. Then take the distributor cap off and look at your rotor... the pickup on the rotor should be pointing roughly towards the driver's side front corner of the truck, or where the radiator cap would be on a fullsize chevy truck. If that is all right, then It would have to be the injectors dumping too much fuel in the motor. Injectors would run you around 85 dollars a piece, so I would check all the exterior stuff first. If you have access to a fuel pressure guage, you might also check your fuel pressure at the TBI inlet... It should be around 13 to 15 pounds. If you don't already have it, you probably need the in-tank pump, strainer and pickup from the suburban as well. Let me know how things go, If the system says you have too many followups, just start a new thread and I'll do whatever I can to help. Check that timing at TDC though, because that sounds like the problem to me.
