Maybe everyone here can help...

I bought this truck (1995 Chevy Blazer, 4.3L V6) about a month ago. I got it for a good price (luckily). The previous owner told me he replaced the 'spider injector'.

Anyway, I knew the truck had a fuel leak. I took a look at it and it turned out to be the fuel sender. So, I replaced the fuel sender and that problem was solved, no more leaky fuel or a gas smell (phew)!

Anyway, I noticed after this that it ran a little better, but that it doesn't have a lot of power going uphills/highway. It just does not want to accelerate.

I started to diagnose things that could possibly be wrong. I'll go in order.

1) I removed the MAP sensor to take a look at it. It had a little oil in the port. I cleaned it up and replaced it. Checked the PCV valve and vacuum lines. Everything looked good vacuum wise. No change

2) I removed the EGR valve, cleaned and replaced with screened gasket. Previous gasket was screened and the valve was not too dirty. No change, still bogs at highway speeds/hills.

3) I replaced fuel filter/air filter/cap/rotor/plugs/wires. Man was the rotor corroded! I'm amazed it ran at all! This helped a bit, but still the same issue.

4) I picked up a new TPS (throttle position sensor), and removed, cleaned and replaced IAC. It wasn't all that bad. No real change.

5) I took the MAP sensor off a '97 skylark I own and put it on the Blazer (its the same MAP sensor, hey why not?). Actually ran a little worse. I didn't clear the ECM this time but probably should have (you know, disconnect the battery for 30 minutes).

6) I was thinking that it was possibly a clogged cat, or a restricted cat. I bought a vaccum gauge and did some testing. Vacuum was steady at 17-18PSI at idle. I brought the throttle up to 2500RPM for several minutes and the vacuum did not drop.

7) I bought a timimg light, and disconnected the timing connector by the ECU, and timed the engine. It was a pain to do honestly. I just saw a reference mark on the pulley and a notched thing on the timing chain cover. I assumed that lining them up was 0 degrees. It was actually off quite a bit and the truck really didn't want to run very well with the timing connector disconnected. I set that and the idle cleaned up, reconnected everything and went for a test run. Same problem, but it has a little more power at takeoff than it used to.

8) I checked the fuel pressure, but I don't think it was on the rail all the way, I'm going to do that tomorrow and let you know.


One thing I noticed is that when the truck is in open loop, it runs BETTER. I don't know what that means yet, but I assume some sensor may be off? I don't know how to force the truck into 'open loop' mode. I tried to disconnect the MAP sensor and it would just stall, so maybe someone has a better idea on how to do this.

I towed a 1000 pound boat with it a few days ago, and man it struggled to get up to 55 mph. I could push the throttle to the floor and not gain anything at some points! Its a 4.3L engine it should do a little better than that! My 3.1L car would pull it way better than this truck!

So, does anyone have any suggestions on what I should do next? I'm left with fuel pump (my next approach, I should have changed it when I did the fuel sender! oh well!), or exhaust backpressure, but the vacuum test didn't show that. Once I held my hand on the exhaust to see the pressure at idle and it was pretty good honestly.

I own a snap-on scanner (I was one of the designers ), and I attached a picture of all the PIDs when the problem was occuring. Its toward the right of the picture. I was gunning the engine and it was just not doing it.

Also, I never really heard pinging, backfires, etc, but maybe its happening and I just can't hear it.

Thanks for your help everyone!!!!!!!!!!

Jim

 

Hit the cat gently with a rubber mallet or your fist. If you hear marbles, it's bad.

Unscrew the O2 sensor and see if it has more power (it will be LOUD). If it does, the cat is bad.

 

Thanks for the info, I hit the cat, and I didn't hear a thing.

Today, I strapped my fuel pressure gauge to the hood and went for a drive. I saw that the fuel pressure was low (~50PSI), which is bad from what I read correct?

Fuel pressure varied between 50 - 63PSI depending on throttle.

I noticed that when I lightly press the accelerator, the pressure oscillates +-4psi in a rapid fashion (the injectors firing). Is this normal behavior? It seems to be always there to some degree, but worse when you just press lightly.

I did the uphill thing as well. I noticed a slight drop in overall pressure with light acceleration ( maybe to 46 PSI ), but when I hit the accelerator harder, it would climb to about 60psi.

Also, after turning off the motor, I watched the pressure fall time. It remained steady (actually went up a bit, 2-3PSI) for about 15-20 minutes. Sounds like my regulator is good at least right?

Anyway, is the fuel pump suspect?

Thanks very much for your assistance!

Jim

 

Sounds like the regulator and the check valve in the pump are both okay.

What are the KOEO numbers for the fuel pressure? Have someone turn the key while you watch the gauge...During the 3 sec. prime, the number should be slightly higher than after the prime; that is normal.

 

 

If the regulator is a problem, yes you can replace just that part without touching the rest of the spider. It's about $40 at Autozone and includes the tamper-proof Torx bit needed to remove the old and install the new.

 

Well, I had previously put a resistor in the IAT sensor to fool the engine to think it was running at 57F. I plugged the IAT sensor back in and it would surge and stumble at acceleration. Uggg..

I tried to disconnect the Linear EGR valve to see if possibly it was some sort of EGR problem. It still stumbled. I didn't think to hook up my scanner to see if it was in 'open loop' or not, because when I run in open loop (for the first fiew minutes) the thing runs like a dream.

I tried to get the O2 sensor out, but its really stuck in there. I'll have to torch the pipe to get that baby out I'm afraid.

 

Well, I disconnected the O2 sensor from the computer.. the thing ran a LOT better! go figure!

So, I'm leaning on the O2 sensor being the culprit, or the injectors.

I found an exhaust hole by the O2 sensor (in front of it).. maybe this is causing the O2 sensor to be sluggish as well.

 

Using your scanner did you look at the live data from the o2 sensors? Bank one should be moving quickly from the 100 range up to 8-900 range bank 2 will do the same but slower
Bank #1 is the sensor that controls a lot so if it's not reacting correctly I would change it out
Any DTC 's

 

I took a look at them.. I actually only seem to have 1 O2 sensor in the truck as well.

Anyway, Change it out, hah! I can't get the damn thing off! I tried a 5 foot breaker bar, and I'm worried about ripping the pipe at this point..

It won't budge.. Tried everything, torch, PB blaster, etc.