BC

I need to fix this, its driving me crazy. A bobble or miss that gets worse with heat and altitude in my "new" 95 chevy tahoe. Yes, its a "light" tow vehicle, but it'll do for me now as its only going to tow an open trailer with one 928 race car.

I have replaced the plugs, wires, rotor, cap, and have ran an entire can of seafoam through the intake. It has gotten a little lessened now after all this, but its still there and I can't trace it down. Just at shove off, almost like a broken motor mount, and under load on a hill. The EGR valve is not holding vac, and I guess its replacement may be next, but I wish not to spend good money after bad since am building a big block to put in here anyway. Something fun like a 502 or 572.

Anyway, any experience here? Its exacerbated by load, and when it was really bad (5000 feet, 99 degrees) it was shaking the whole truck.

amondc

A few things to check. If i remember right that has the TBI intake with the 2 injectors, if you look thru the throttle bodies with a flashlight towards the back right corner you can see the fuel pressure regulator, this leaks and causes a miss on #7, and 8 cylinders. Also the distributor pickup get weak and will cause a miss but usually it will just kill the engine, if you end up buying another distributor get it from a chevy dealer new not Oreilly's etc they are no good becuase that do not replace the pickup when the "reman" them. Check fuel pressure so see if you have enough and that it does not drop when you shut the key off. Finally there could be a coolant leak on the upper intake very common problem on chevy's.

Hopefully some of this will help out and fix the problem.

If you have any questions let me know
Chris

BC

I smell coolant sometimes. I just checked all plugs again and they are brown on one side after only 2700 miles. Very brown. I have a pic and will upload it.

You are saying the FPR is INSIDE there somewhere? The injectors are streaming more than spraying right now as well.

amondc

I am sorry the FPR is not back under the intake on this engine its just infront of the injectors.

Generally the coolant leaks appear at the corners of the gasket around the intake look there and see if you see anything.

If the injectors are not really spraying then they could be stuck open where they will just dump too much fuel in the engine. It sounds like this is your problem because they should be pulsing and spraying the fuel into the motor

Veloce Raptor

Also try higher octane gas at high temps & altitude when towing.

BC

Thanks alot. They are clicking, so I had assumed they are closing, but the spray pattern is more like a cone setting on a hose then what I have seen pintle injectors do on my 928 (I know, spraying atomized fuel in the open is dangerous, but I had to see)

I drove it a while again, really got it warm. Its running through the rev range much better, but still missing, and losing power when it happens. Comes, goes, comes goes. And at throttle tip in at a stop, it feels like three or four "junts" like broken motor mounts.

amondc

Do you have a way to measure fuel pressure? They don't really spray like normal injectors do sometimes you can take a timing light and and get a better view of the spray pattern as long as it is a spray and not a drip you should be ok.

Kinda running out of ideas, I will think on it some more and get back with you

eclou

there are alot of great tech articles on websites like fullsizechevy.com . Any check engine lights? You could scan the OBD I diagnostic port for clues

BC

Its a 95 - I was not aware of any real info available from the computer?

BC

Thanks for the website. Still salivating at the Dart blocks on ebay that would handle a 632 cubic incher. Don't suppose I could coax those past 15mpg?

SundayDriver

GM was the one that lead the charge to ODBII and, as such, many of their earlier vehicles will give you a lot of data. You probably need more than a generic OBD scanner - Snap On, OTC, Launch, etc. If you can get an experienced mechanic to look at the data, it would help. There is far more to look at than codes - you can check all sorts of real time data from these advanced scanners.

Many of these GM engines are very prone to intake manifold & plenum leaks. A quick check (be very careful and keep a fire extinguisher handy) is to spray a flammable solvent around the manifold at idle. See if the idle quality changes when you hit certain areas.

BC

Thanks SundayDrover. The Chevy dealer is local and I can have them take a look, but I avoide stealerships at all cost. Its ironic that I have fixed more subtle issues than these on a 20 year old 928 and within a smaller time frame. A 95 Chevy tahoe is stumping me.