I have a 73 cruiser w/ a chev 350 and a 350 auto. It had a edelbrock perforfer intake w/ a q-jet carb that always ran rich at high altitudes.So I went to 88 TBI set-up . At the time of the conversion the mechanic did a compession test and 7 of the cylinders ran at 145-150 lbs but there was 1 at 85 lbs Ever since i had a mechanic install this set-up it will run hot 225-230 degrees. No matter what the temp is ouitside. Last night i drovre it in 65 degree weather for about 25 miles (65mph) and the temp ran at 228 degrees. Ever since the mechanic did this conversion for me (3 weeks ago) the cruiser runs hot. The radiator is the stock one from JT outfitters and is only 1 year old w/ maybe 800 miles on it. I have changed every possible thing that the mechanic has told me that was the cause of my overheating. In the last 2 weeks this what i put on it new Fan Clutch, Fan, Thermosat, Hoses w/ springs, Belts, Cap-13lbs, Waterpump, Intake gaskets w/o the restristors, Shroud , New coolant mixture. Lots of money spent!! I did all of the following items myself. Now the mechanic says that the weak cylinder is the problem because of the excess fuel going into the exhaust is making the oxygen senor read the exhaust as running rich so it is leaning the motor way out and causing the engine to get hot. I could really use some imput as i really don"t want to pull the heads because everythind he has told me didn't work so far and i can,t just keep spending money.

What he said is VERY possible and in fact likely. I am in the process of re-rebuilding my 91 TPI 305 because the rings did not seat and it had about 100-110 psi compression and it ran hot(195 at idle and about 225 on the highway.) The incomplete combustion in the low compression cylinder can cause unburnt fuel(event he most minute amount can f-up and O2 sensor. The 02 sensors are VERY narrow band and even a little rich will be detected and the computer will try to compensate for it.

Isthe cylinder with low compression on the same side of the engine as the O2 sensor in the exhaust manifold? If not this might not be the problem as the TBI manifolds had the )2 sensor on one side only IIRC...

-Brett

When it comes to O2 sensors, the first recommendation I got from a local pro-hot rod shop was to use a “heated sensor”. This helps with the accuracy of what it is reading and provides a more consistent signal. I pitched the one wire stock unit that was in my original TPI harness and picked up a “universal” 3 wire O2 sensor from the local parts house. The instructions with the sensor sucked but did indicate one of the wires as the signal wire (black on mine) and the other two as (+) and (-). (Both white on mine, polarity does not matter; it just needs juice to one and ground to the other) I wired it in with switched (+) and spliced in the signal wire to my harness. The heated jobs cost more (of course!) mine was in the low $30’s. This may not completely fix your problem, but you will be getting a cleaner signal to the CPU.

Yes, the O2 sensor is on the same side as the low cylinder. Thanks for your both inputs on this subject. I will see what else other people say on this board. But your both saying the same as the mechanic. He also says he has a set of Vortec heads that are all ready to that he can install. He wants $600.00 for them (not including labor). Is that out of line on the price? And will they make that much difference in performance?

Vortec or Truck heads(L31) designation if I remember correctly can be purchased from any GMPP dealer for around $430.00 per pair assembled.

THey are a great head, but the are several caveats to using them.

Look around and be sure you are getting the right info.

HTH

Originally posted by jssena
Yes, the O2 sensor is on the same side as the low cylinder. Thanks for your both inputs on this subject. I will see what else other people say on this board. But your both saying the same as the mechanic. He also says he has a set of Vortec heads that are all ready to that he can install. He wants $600.00 for them (not including labor). Is that out of line on the price? And will they make that much difference in performance?

Rugburn is right the GM dealers are selling them cheep as brand new sets. Talk with the GM parts guys, I don't think they will bolt up to a block older than 95'. It is either that or it is the intake that will not bolt up. Just an FYI to ask some other Q's from a GM friend.

Helocat: Your right the tbi intake will not bolt up to ther older heads. There are 2 bolts on the intake in the center on both sides. So we needed to drill my heads so the intake would bolt up. But good to know that the heads are very reasonable from GM. I told by a couple local mechanics that a weak cylinder should not effect the O2 sensor. I'm still confused as to the O2 sensor function.

Originally posted by jssena
Helocat: Your right the tbi intake will not bolt up to ther older heads. There are 2 bolts on the intake in the center on both sides. So we needed to drill my heads so the intake would bolt up. But good to know that the heads are very reasonable from GM. I told by a couple local mechanics that a weak cylinder should not effect the O2 sensor. I'm still confused as to the O2 sensor function.

If you can swing the $30 I would change the O2 sensor out. The other one that is most comon to have issues with TPI's (I am sure the same with TBI's) is the water temp sensor. ($12.00 from GM)

Just some ideas.

ttt

I haven't yet fired mine up. I have 71 FJ40 w/327 & TH350. I just installed the TBI from an 88 Chev 350. I am completeing the wiring now, next the plumbing. I had the Edelbrock performer manifold and cam. Edelbrock told me the preformer cam is not compatible with a computer controlled engine. I put in the Crane cam for the TBI truck. I used the TBI manifold, wiring, distributor, and all the sensors. I was going to use my orig heads, but found TBI heads on EBAY (so I didn't have to hog out the 4 center bolts on the manifold)

What did you do for the heater hose fittings? The JTR book on conversions says the one out of the manifold to the heater needs a restriction (can cause hot run). The one I just got for 5/8 hose only has a 3/8 hole in it. They claim it could be restricted even down to 1/4.
What engine did your TBI come from? The color code on 350 injectors is orange and black(on the tabs between the connector pins). Did you use TBI manifold or an adapter?
Has the timing been set with the EST wire disconnected (base timing is set with the wire disconnected)? It does sound as though it is running lean. I believe the poor cylinder would drive the computer lean. Have you tried running it with the O2 disconnected? I know it will set a code, but it would run at default settings and maybe help to diagnose.

Do you have any pix of your setup? Where did you put your ECM?
If you want to send me Pix maybe I'll see something. I can post them for you.

why not just move 02 sensor bung to the other manifold, and get a new sensor. cheap and easy fix until you can afford to fix the compression prob.

-later!

Thankx elf cruiser i didn't even think of that simple Fix. I did that today with no improvement in temp reduction. But that fix was alot cheaper than trying a new set of heads.
Yoda As for the Tbi i used was off a 88 chev 1/2 ton p.u.. The intake gaskets used were open in front for the water jackets and the rear water jackets were blocked w/ a restrictor, the restrictor had a pin hole in the restrictor. I questioned that but was told those were the correct ones to use. When i changed the intake gasket last week the intake gasket io received came w/ a restrictor plate that had a hole the size of a dime in each of the rear restrictors. I just went ahead and left them out completely to allow full water flow. That still didn't make a difference in heat build-up.
I did use the factory 88 intake that came with that truck. I used painless wiring and mounted the ECM in the glove box . But that is a tight fit and doesn't look real clean with everything in there. As for pix i can possible send some later as i'm on vaction here in Oregon. E-mail me your E-mail at jsena@sosinet.net

ttt

Water restrictor plate? I thought the little metal plates with holes were for the EGR restriction on earlier carbed motors...

Try pulling the thermostat and drilling a 1/8" hole in it... this can help burp it and get rid of any air...

I cut out the inner fender wells in an attempt to help the cooling. I have not put the otor together, but I will give yyou a report once done...
-Brett