Sequential to MPFI replacement kits??

[bowhuntrrl]

I'm having some issues lately with my '98 Tahoe 5.7 with Central Sequential FI and diagnostics point to 3 bad poppet valves. The issue I.m having is extra cranking to start and also a skip(misfire) when passing gear is kicked down. The plugs and wires have been replaced and the ignition system doesn't seem to be the problem.Fuel pump pressure and volume is good but 3 poppets won't hold pressure. I have run across a conversion kit at NAPA, Advance, and Autozone to replace the Central Sequential with a multiport system. All look to be about the same except Autozone and Advance are GP Sorensen and NAPA says Echlin.

Have any of you tried these out and what are the results. Will they give me the same fuel economy as the old system or maybe even better ?? Most importantly, do they work?? If this is not what you would use to fix the problem, what is ?? Thanks.

[Jeremy-WI]

Check prices at gmpartsdirect.com or rockauto.com and get the AC Delco unit, I've been using the Delco version for about 5 years now. Your fuel economy will only get better if there is something wrong with the CSFI system, the injectors are rated the same. The GM part number for the V8 mpfi is 93441235, you may want to get a new upper intake gasket set, but you don't need a new bracket, just do a internet search for 93441235 and you should be able to find the part number for the gaskets

[laxman21]

Ebay...

I got mine for $235 shipped to my house.


I got the borg warner one. They are all the same, delphi, ac delco, borg warner. The first two just cost more.

I got mine from seller O2sensors..


http://cgi.ebay.com/ebaymotors/97-98...=p4506.c0.m245

http://cgi.ebay.com/ebaymotors/96-97...Q5fAccessories

[bowhuntrrl]

I thought that I would report back on what happened. Two days before I was going to have my technician replace the fuel spider with the conversion, my fuel pump died. So as a final tally, I ended up replacing the fuel pump, fuel filter, fuel spider with the replacement MPFI kit. I also had installed new plugs, wires, cap and rotor chasing the skip and hard start problems.

The good news is that it starts and runs fantastic !!! The engine barely needs to turn over before it starts. It's too early to comment on fuel consumption, but the performance is great. I can cruise down the road at 50-55 barely touching the throttle. Some of that may be due to the throttle body spacer that I had installed previously , which I feel gave me a bit of added torque. So far, so good !!

[bowhuntrrl]

Well, I finally burned through the 30 gallon tank after this big fix. The bad news is that I lost almost 5 mpg !!! The truck runs better than it has in years, but now it has gone from 16 mpg around town to a dismal 11 mpg.

Does anyone know if that's the nature of this conversion or can something else be causing this??

[MT-2500]

A good one should even help it.

Go over your tune up end for problems and be sure to check for correct fuel pressure.

[Jeremy-WI]

My guess would be an intake leak around the injectors electrical connector. The conversion did not change my mpg, I did it because the poppet valves were a known problem and I knew my fuel pressure regulator was bad, so I decided to kill two birds with one stone

[bowhuntrrl]

Originally Posted by Jeremy-WI

My guess would be an intake leak around the injectors electrical connector. The conversion did not change my mpg, I did it because the poppet valves were a known problem and I knew my fuel pressure regulator was bad, so I decided to kill two birds with one stone

I did mine because of 3 leaking poppet valves and pressure reg also bad. The truck was skipping and bucking, but still getting 16 mpg !!! Now it runs better than it ever has in the 5 years that I've had it but gets a dismal 12 mpg.

If it was a vacuum leak, wouldn't it manifest itself as a skip or lack of power ?? It has neither of these symptoms. I went to check the vacuum today and can't find any place on the intake to plug the vacuum gauge into. Where can I tap in and what should it be for in/hg ??

[bowhuntrrl]

After several months of documenting gas mileage and searching for problems, I am at my wits end !!! Fuel consumption is running between 11.5 and 12.2 mpg, down from a constant 16 mpg. This week I took it in and had all the sensors scanned. Everything is reading as it should. The air/fuel ratio shows as 14.5 to 1, which is good for power, but not for economy. My intake manifold vacuum is 21" hg. Other than a defective fuel spider unit, I really don't know what can be causing this problem.

Does anyone have any ideas ??

[Jeremy-WI]

Was the intake vacuum reading from the MAP sensor or a vacuum gauge? If it was from the MAP sensor, you have a leak somewhere if the reading is at idle

[bowhuntrrl]

Originally Posted by Jeremy-WI

Was the intake vacuum reading from the MAP sensor or a vacuum gauge? If it was from the MAP sensor, you have a leak somewhere if the reading is at idle

Reading was from a vacuum gauge. The tech that was checking all this read the MAP sensor and the reading was somewhat confusing. His scanner was an OTC and it read 9 inches. This didn't sound right so he checked another GM that was known good and got a similar reading. He seemed to think that the firmware was perhaps backwards being 30" reference minus the 9" which equaled the 21" reading that we got from the gauge.