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Discussion Starter #1
My Suburban is having a running problem, and it's been having it since I picked up the truck a few weeks back. What is happening is I will give the truck throttle and up to a certain point, it seems to behave as expected. Past a certain throttle/power level, the truck simply will not give me any more power, and starts to decrease. It feel to me like there is not enough fuel going to the motor, probably a dying fuel pump. So far I have done the following:

-Fuel Filter
-Plugs/wires/cap/rotor
-TPS
-Ignition coil
-Fixed vacuum leaks

One friend of mine said that it could be a clogged cat, or sometimes on these trucks the gasket between the TBI and the intake manifold can go bad, and that can cause a problem of this nature. However there is no cat, and I don't understand how that gasket could make this sort of change. So, my questions are as follows:

1) Any other potential sources of my problem to check first?
2) Is there an easy way to check fuel pressure on my TBI before going out and replacing the fuel pump?
3) Is there an easier way to replace the fuel pump than dropping the tank? It still has about 35-40 gallons of fuel in it.
 

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:)The old tbi's do not have a shrader valve to quickly check fuel press, will have to tee in after fuel filter to check. Also press is one thing, also make sure flow does not drop off at higher rpm. Had one where the customer did his own work and actually twisted one of the flex lines, press stayed high but flow droppped off. Also quick check, base timing...make sure you disconnect the single wire, usually around heater motor inside. As for the tb base gasket, if it was leaking you would have a high idle, the iac counts would be off and you could set a lean code. good luck.
 

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Have the fuel pressure checked under full throttle. I have a gauge adapter that installs in place of the filter and allows a hookup. Call a few auto shops and you'll find one that can do it.

Vernon
 

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DIRTY AIR CLEANER??? MAP sensor, TP sensor, fuel volume+pressure(9-13psi), clogged exhaust(even W/O kitty), pick up coil in dist, coil, module, timing, I can go on from here but first thing I'd check is fuel.

Timing disconnect is a brown/black stripe wire outside the main harness, behind the plastic relay cover. TBI gasket will not do this, just high idle. Check O2 sensor for a false rich reading which will cause ECM to lean the mixture to compensate.

Older TBI units are known to plug up the internal vacuum passages, pull the TBI and flip it over, plugged passages can restrict vac to map sensor, use a small screwdriver or drill bit (by hand) to clear
 

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Reversed #7 and #5 plug wire or bad plug wire. Verify installation (1-8-4-3-6-5-7-2) and test each wire with an ohm. If either of the above occurs, there is normally no SES light, and it will idle smooth but screw up at heavy loads.
 

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Big block TBI runs 28 psi fuel pressure. I use a refrigeration bullet piercing valve on the fuel line. It clamps over the line and provides a #4 flare fitting for a gauge. It has a valve built in and comes with a flare cap. You just leave it there, handy for future problems. Cost about $6.
 

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I once had an '89 454, TBI dually that acted like somebody pulled a couple of plug wires off; in fact, the fuel filter had gotten plugged and it felt like it had lost about 50 hp! Back then, I bought a lot of stuff from Turbo City in Anaheim, California, oversized throttle body, matched-injectors, gasket kits, etc. If you decide to pull the manifold, consider replacing it with an Edelbrock TBI version; if you really want to wake up your truck, go all the way and add a Crane Compu-cam (and maybe some higher ratio roller rockers, but only on the exhaust valves) and then hang on...!
 

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Discussion Starter #8
Sorry for the slow response - been very busy the past week or so.

Well, I did the plugs/wires/cap/rotor which significantly helped the running condition. Yes, the firing order is correct (1-8-4-3-6-5-7-2). I already did TPS, CTS, coil, fuel filter. The MAP on this truck is actually taken off of the intake manifold, not off of the TBI unit itself. My idle is not high. Something interesting to note is that when the truck has been sitting overnight, I have to crank it a bit longer before it starts than I do when I go to lunch and then go home. So, I am thinking that may be the fuel pump having problems building pressure.

I haven't checked the fuel pressure, but I've started dropping the tank to change the fuel pump, so that's getting done. Hopefully it will solve my problem.

ex3056, can you give me any more details about these performance upgrades and what you did to your '89? In stock form, this truck makes something like 230 hp and 385 lb-ft. I would like to see something more in the 300 hp and 500 lb-ft range, without raising the RPMs. Of course I'm also seeing some fun supercharger kits... :)
 

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My '91 has a Competition Cams roller cam and roller rockers. It is very mild cam with great vacuum at idle and tons of torque. It is also 10:1, which you probably don't want to do because it has to have premium gas. I run it on propane which likes higher compression. Even with stock compression, you would probably be close to your desired numbers with a mild roller cam. The rockers free up another 20 hp or so, and probably the roller lifters do the same.
 

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Discussion Starter #10
My goal is to keep the stock rev range (current redline is 4000 rpms) and just have more power in that range. I don't want to let the motor rev, one of the things I love about big blocks is having all the power without having to rev it. But, since it's TBI I'll also need a chip of some sort to work with it.

marcdeluca, did you find that roller rockers and lifters really freed up that much horsepower? I would suspect if they did then that might also see a slight mileage improvement...
 

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Before I got my Dmax, I had a '00 crew cab with vortec 454, 4:10 gears and 4L80 trans. My '91 that I still have also has the same trans and gears. There is a long hill on a highway near where I live. With the '00, with cruise on, it would have to downshift to 3rd about halfway up. With the '91, I can give it gentle throttle and accelerate from 60 while climbing the hill, never unlocking the converter or downshifting. It probably has 100 ft/lbs more than the stock vortec. The trucks were close to the same weight, the '91 weighing a bit more because of the Dana 60 front axle and NP 205 transfer case being iron. Mine is not a rev motor, it has the stock TBI intake and exhaust manifolds. I rarely have it up to 4000 rpms because it doesn't need to rev to get the work done.
 

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As I mentioned earlier, my truck was an '89 454 dually, regular cab 4X4 (with a fiberglas shell and carpet kit) and a Turbo 400 (Transgo shift kit); it had a Dana 60 rear end with 4.10 gears. I put some Doug's Tri-y headers on it with a 3" exhaust and Magna Flow muffler (very quiet set-up). I added an Edelbrock TBI manifold (painted flat black for "stealth") and Turbo City oversized throttle body, matched-flow injectors and an adjustable fuel pressure regulator (I think I also had one of their "chips" in my computer). My motor came stock with flat tappet hydraulic lifters, so when I changed the cam, I stayed with this arrangement but replaced it with the Crane Compu-cam and lifters; eventually I added some cast, larger ratio roller rockers but can't remember the manufacturer (probably Comp Cams). Every item I changed, except the throttle body, was a "smog legal" part [I live in So Cal and they smog check vehicles (visual inspection and tailpipe emissions) every other year]; I'm not sure about the roller rockers being smog legal. In those days, there weren't a lot of choices when it came to hot rodding trucks. When the truck was new, I went to Hooker Headers and asked them if they made headers for it and the salesman thought I was "crazy" for wanting to put headers on my pick up!
 
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